Merge branch 's-draw' into s-gray

Also move the boundary table comment back above its test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

esphome/components/online_image/download_buffer.cpp

@@ -1,5 +1,6 @@
 #include "download_buffer.h"
 #include "esphome/core/log.h"
+#include <algorithm>
 #include <cstring>
 
 namespace esphome::online_image {
@@ -34,6 +35,46 @@ size_t DownloadBuffer::read(size_t len) {
   return this->unread_;
 }
 
+void DownloadSource::compact() {
+  if (this->keep_read_ || this->pos_ == this->start_)
+    return;
+  this->buffer_.read(this->pos_ - this->start_);
+  this->start_ = this->pos_;
+}
+
+int32_t DownloadSource::read(uint8_t *buf, uint32_t len) {
+  const size_t offset = this->pos_ - this->start_;
+  const size_t n = std::min<size_t>(len, this->buffer_.unread() - offset);
+  memcpy(buf, this->buffer_.data(offset), n);
+  this->pos_ += n;
+  return static_cast<int32_t>(n);
+}
+
+bool DownloadSource::seek(uint32_t position) {
+  // Only what is still in the buffer can be read again; a decoder never skips ahead of the download
+  if (position < this->start_ || position > this->start_ + this->buffer_.unread())
+    return false;
+  this->pos_ = position;
+  return true;
+}
+
+bool DownloadBuffer::grow(size_t size) {
+  if (this->size_ >= size)
+    return true;
+  RAMAllocator<uint8_t> allocator;
+  uint8_t *buffer = allocator.allocate(size);
+  if (buffer == nullptr) {
+    ESP_LOGE(TAG, "allocation of %zu bytes failed. Biggest block in heap: %zu Bytes", size,
+             allocator.get_max_free_block_size());
+    return false;
+  }
+  memcpy(buffer, this->buffer_, this->unread_);
+  allocator.deallocate(this->buffer_, this->size_);
+  this->buffer_ = buffer;
+  this->size_ = size;
+  return true;
+}
+
 size_t DownloadBuffer::resize(size_t size) {
   if (this->size_ >= size) {
     // Avoid useless reallocations; if the buffer is big enough, don't reallocate.

esphome/components/online_image/download_buffer.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "esphome/components/runtime_image/image_decoder.h"
 #include "esphome/core/helpers.h"
 #include <cstddef>
 #include <cstdint>
@@ -35,6 +36,8 @@ class DownloadBuffer {
 
   void reset() { this->unread_ = 0; }
   size_t resize(size_t size);
+  /// Make the buffer at least size bytes, keeping the unread data. Returns false if the allocation failed.
+  bool grow(size_t size);
 
  protected:
   uint8_t *buffer_;
@@ -43,4 +46,35 @@ class DownloadBuffer {
   size_t unread_;
 };
 
+/**
+ * @brief Lets a decoder read a download as it arrives, from the download buffer.
+ *
+ * The decoder reads at its own position in the buffer. Bytes it has read stay there until compact() drops
+ * them, and compact() keeps everything while set_keep_read(true) is in effect, so the decoder can seek back
+ * while it reads the headers.
+ */
+class DownloadSource : public runtime_image::DecodeSource {
+ public:
+  explicit DownloadSource(DownloadBuffer &buffer) : buffer_(buffer) {}
+
+  /// Start again at the beginning of a new download, keeping what is read
+  void reset() {
+    this->start_ = 0;
+    this->pos_ = 0;
+    this->keep_read_ = true;
+  }
+  void set_keep_read(bool keep) { this->keep_read_ = keep; }
+  /// Drop the bytes the decoder has read, to make room for more of the download
+  void compact();
+
+  int32_t read(uint8_t *buf, uint32_t len) override;
+  bool seek(uint32_t position) override;
+
+ protected:
+  DownloadBuffer &buffer_;
+  size_t start_{0};  // Position in the download of the first byte in the buffer
+  size_t pos_{0};    // Position in the download the decoder reads next
+  bool keep_read_{true};
+};
+
 }  // namespace esphome::online_image

esphome/components/online_image/image.py

@@ -22,6 +22,8 @@ DEPENDENCIES = ["http_request"]
 CODEOWNERS = ["@guillempages", "@clydebarrow"]
 
 CONF_ON_DOWNLOAD_FINISHED = "on_download_finished"
+CONF_ON_DOWNLOAD_STARTED = "on_download_started"
+CONF_ON_DOWNLOAD_PROGRESS = "on_download_progress"
 CONF_UPDATE = "update"
 
 online_image_ns = cg.esphome_ns.namespace("online_image")
@@ -43,7 +45,9 @@ ONLINE_IMAGE_SCHEMA = (
             cv.Optional(CONF_REQUEST_HEADERS): cv.All(
                 cv.Schema({cv.string: cv.templatable(cv.string)})
             ),
+            cv.Optional(CONF_ON_DOWNLOAD_STARTED): automation.validate_automation({}),
             cv.Optional(CONF_ON_DOWNLOAD_FINISHED): automation.validate_automation({}),
+            cv.Optional(CONF_ON_DOWNLOAD_PROGRESS): automation.validate_automation({}),
             cv.Optional(CONF_ON_ERROR): automation.validate_automation({}),
         }
     )
@@ -96,9 +100,17 @@ automation.register_apply_action(
 
 
 _CALLBACK_AUTOMATIONS = (
+    automation.CallbackAutomation(
+        CONF_ON_DOWNLOAD_STARTED, "add_on_download_started_callback"
+    ),
     automation.CallbackAutomation(
         CONF_ON_DOWNLOAD_FINISHED, "add_on_finished_callback", [(bool, "cached")]
     ),
+    automation.CallbackAutomation(
+        CONF_ON_DOWNLOAD_PROGRESS,
+        "add_on_progress_callback",
+        [(float, "progress"), (cg.size_t, "bytes_read")],
+    ),
     automation.CallbackAutomation(CONF_ON_ERROR, "add_on_error_callback"),
 )
 

esphome/components/online_image/online_image.cpp

@@ -4,6 +4,7 @@
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 #include <algorithm>
+#include <cmath>
 #include <cstdio>
 
 ESPHOME_LOG_TAG(TAG, "online_image");
@@ -15,6 +16,11 @@ static const char *const IF_MODIFIED_SINCE_HEADER_NAME = "if-modified-since";
 
 namespace esphome::online_image {
 
+// Time one loop pass may spend reading, and decoding a JPEG as it downloads
+static constexpr uint32_t PASS_BUDGET_MS = 20;
+// Shortest time between two on_download_progress calls
+static constexpr uint32_t PROGRESS_INTERVAL_MS = 100;
+
 OnlineImage::OnlineImage(const std::string &url, int width, int height, runtime_image::ImageFormat format,
                          image::ImageType type, image::Transparency transparency, image::Image *placeholder,
                          uint32_t buffer_size, bool is_big_endian)
@@ -140,8 +146,12 @@ void OnlineImage::update() {
     return;
   }
 
-  // JPEG requires the complete image in the download buffer before decoding
-  if (format == runtime_image::JPEG && total_size > this->download_buffer_.size() &&
+  // A JPEG of known size is decoded as it arrives, so the download buffer only has to hold its headers.
+  // Otherwise the decoder needs the complete image in the buffer.
+  this->streaming_ = total_size > 0 && total_size <= INT32_MAX && this->decoder_supports_source();
+  this->stream_started_ = false;
+  this->source_.reset();
+  if (!this->streaming_ && format == runtime_image::JPEG && total_size > this->download_buffer_.size() &&
       this->download_buffer_.resize(total_size) == 0) {
     // resize() logged the failed allocation; the next update() allocates the configured buffer again
     this->end_connection_();
@@ -152,6 +162,8 @@ void OnlineImage::update() {
   ESP_LOGI(TAG, "Downloading image (Size: %zu)", total_size);
   this->start_time_ = millis();
   this->last_data_time_ = this->start_time_;
+  this->download_started_callback_.call();
+  this->report_progress_(true);
   this->enable_loop();
 }
 
@@ -169,6 +181,11 @@ void OnlineImage::loop() {
     return;
   }
 
+  if (this->streaming_) {
+    this->loop_stream_();
+    return;
+  }
+
   // Check if download is complete — use decoder's format-specific completion check
   // to handle both known content-length and chunked transfer encoding
   if (this->is_decode_finished() || (this->downloader_->content_length > 0 &&
@@ -179,15 +196,22 @@ void OnlineImage::loop() {
   }
 
   // Download and decode more data
-  size_t available = this->download_buffer_.free_capacity();
-  if (available > 0) {
-    // Download in chunks to avoid blocking
-    available = std::min(available, this->download_buffer_initial_size_);
-    auto len = this->downloader_->read(this->download_buffer_.append(), available);
-
-    if (len > 0) {
-      this->last_data_time_ = App.get_loop_component_start_time();
+  if (this->download_buffer_.free_capacity() > 0) {
+    const uint32_t now = App.get_loop_component_start_time();
+    size_t received = 0;
+    int len;
+    do {
+      len = this->downloader_->read(this->download_buffer_.append(),
+                                    std::min(this->download_buffer_.free_capacity(), READ_CHUNK));
+      if (len <= 0)
+        break;
       this->download_buffer_.write(len);
+      received += len;
+    } while (this->download_buffer_.free_capacity() != 0 && millis() - now < PASS_BUDGET_MS);
+
+    if (received > 0) {
+      this->last_data_time_ = now;
+      this->report_progress_(false);
 
       // Feed data to decoder
       auto consumed = this->feed_data(this->download_buffer_.data(), this->download_buffer_.unread());
@@ -255,6 +279,114 @@ void OnlineImage::loop() {
   }
 }
 
+void OnlineImage::loop_stream_() {
+  const uint32_t now = App.get_loop_component_start_time();
+  const size_t total = this->downloader_->content_length;
+  if (this->stream_started_)
+    this->source_.compact();
+
+  if (this->downloader_->get_bytes_read() < total) {
+    if (this->download_buffer_.free_capacity() == 0) {
+      // compact() already ran, so a full buffer means the decoder read nothing in the last pass
+      if (now - this->last_data_time_ >= this->parent_->get_timeout()) {
+        ESP_LOGE(TAG, "Image does not fit in the %zu byte download buffer; increase buffer_size",
+                 this->download_buffer_.size());
+        this->fail_download_();
+        return;
+      }
+    } else {
+      int len;
+      do {
+        len = this->downloader_->read(this->download_buffer_.append(),
+                                      std::min(this->download_buffer_.free_capacity(), READ_CHUNK));
+        if (len <= 0)
+          break;
+        this->last_data_time_ = now;
+        this->download_buffer_.write(len);
+        this->report_progress_(false);
+      } while (this->downloader_->get_bytes_read() < total && this->download_buffer_.free_capacity() != 0 &&
+               millis() - now < PASS_BUDGET_MS);
+      if (len < 0) {
+        ESP_LOGE(TAG, "Error downloading image: %d", len);
+        this->fail_download_();
+        return;
+      } else if (now - this->last_data_time_ >= this->parent_->get_timeout()) {
+        ESP_LOGE(TAG, "No data received for %" PRIu32 " ms", this->parent_->get_timeout());
+        this->fail_download_();
+        return;
+      }
+    }
+  }
+  const bool arrived = this->downloader_->get_bytes_read() >= total;
+
+  if (!this->stream_started_) {
+    // The decoder reads the headers when it opens the image, so wait until they are in the buffer
+    if (!arrived && this->download_buffer_.free_capacity() != 0)
+      return;
+    const int err = this->begin_source(&this->source_);
+    if (err != 0) {
+      // Headers cut short by a full buffer fail to parse, or make the decoder seek past the buffer. Such an image
+      // still decodes once it is all in memory, as it did before JPEG images were decoded as they download.
+      if (!arrived && (err == runtime_image::DECODE_ERROR_INVALID_TYPE || err == runtime_image::DECODE_ERROR_READ)) {
+        ESP_LOGW(TAG,
+                 "The image headers do not fit the %zu byte download buffer, so the whole image is downloaded "
+                 "before it is decoded; increase buffer_size to decode it as it downloads",
+                 this->download_buffer_.size());
+        // grow() logs a failed allocation
+        if (this->download_buffer_.grow(total)) {
+          this->streaming_ = false;
+        } else {
+          this->fail_download_();
+        }
+        return;
+      }
+      ESP_LOGE(TAG, "Error decoding image: %s", runtime_image::decode_error_to_string(err));
+      this->fail_download_();
+      return;
+    }
+    this->source_.set_keep_read(false);
+    this->stream_started_ = true;
+    // Opening the image and allocating its buffer is enough for one pass
+    return;
+  }
+
+  do {
+    const int result = this->decode_step();
+    if (result == runtime_image::DECODE_STEP_MORE)
+      continue;
+    if (result == runtime_image::DECODE_STEP_DONE) {
+      this->finish_download_();
+    } else if (result == runtime_image::DECODE_STEP_NEED_DATA) {
+      if (!arrived)
+        return;
+      // JPEGDEC only waits for bytes short of the size it was given, so this guards against a hang
+      ESP_LOGE(TAG, "Download ended before the image was complete");
+      this->fail_download_();
+    } else {
+      ESP_LOGE(TAG, "Error decoding image: %s", runtime_image::decode_error_to_string(result));
+      this->fail_download_();
+    }
+    return;
+  } while (millis() - now < PASS_BUDGET_MS);
+}
+
+void OnlineImage::report_progress_(bool force) {
+  const uint32_t now = App.get_loop_component_start_time();
+  const size_t bytes = this->downloader_->get_bytes_read();
+  const size_t total = this->downloader_->content_length;
+  // The last bytes are always reported, so a progress bar reaches 100%
+  if (!force && now - this->last_progress_time_ < PROGRESS_INTERVAL_MS && (total == 0 || bytes < total))
+    return;
+  this->last_progress_time_ = now;
+  const float progress = total > 0 ? std::min(100.0f, bytes * 100.0f / total) : NAN;
+  this->download_progress_callback_.call(progress, bytes);
+}
+
+void OnlineImage::fail_download_() {
+  this->end_connection_();
+  this->download_error_callback_.call();
+}
+
 void OnlineImage::finish_download_() {
   // Must be read before end_decode() ends the decoding session
   bool decoder_finished = this->is_decode_finished();
@@ -288,6 +420,8 @@ void OnlineImage::end_connection_() {
     this->downloader_ = nullptr;
   }
   this->download_buffer_.reset();
+  this->streaming_ = false;
+  this->stream_started_ = false;
   this->disable_loop();
 }
 

esphome/components/online_image/online_image.h

@@ -16,6 +16,10 @@ using t_http_codes = enum {
   HTTP_CODE_NOT_FOUND = 404,
 };
 
+/// Largest download read(). A read() blocks until it has every byte it asked for, so this bounds how long one loop
+/// pass waits on a slow link.
+static constexpr size_t READ_CHUNK = 1460;
+
 /**
  * @brief Download an image from a given URL, and decode it using the specified decoder.
  * The image will then be stored in a buffer, so that it can be re-displayed without the
@@ -70,9 +74,17 @@ class OnlineImage final : public PollingComponent,
    */
   void release();
 
+  /// Called when the server has accepted the request and the image starts to download
+  template<typename F> void add_on_download_started_callback(F &&callback) {
+    this->download_started_callback_.add(std::forward<F>(callback));
+  }
   template<typename F> void add_on_finished_callback(F &&callback) {
     this->download_finished_callback_.add(std::forward<F>(callback));
   }
+  /// Called with the percentage downloaded (NAN when the server did not send the size) and the bytes read so far
+  template<typename F> void add_on_progress_callback(F &&callback) {
+    this->download_progress_callback_.add(std::forward<F>(callback));
+  }
   template<typename F> void add_on_error_callback(F &&callback) {
     this->download_error_callback_.add(std::forward<F>(callback));
   }
@@ -81,12 +93,20 @@ class OnlineImage final : public PollingComponent,
   bool validate_url_(const std::string &url);
   void end_connection_();
   void finish_download_();
+  /// loop() for a JPEG that is decoded as it downloads
+  void loop_stream_();
+  void fail_download_();
+  /// Reports download progress, at most every PROGRESS_INTERVAL_MS unless force is set
+  void report_progress_(bool force);
 
   CallbackManager<void(bool)> download_finished_callback_{};
   CallbackManager<void()> download_error_callback_{};
+  LazyCallbackManager<void()> download_started_callback_{};
+  LazyCallbackManager<void(float, size_t)> download_progress_callback_{};
 
   std::shared_ptr<http_request::HttpContainer> downloader_{nullptr};
   DownloadBuffer download_buffer_;
+  DownloadSource source_{download_buffer_};
   /**
    * This is the *initial* size of the download buffer, not the current size.
    * The download buffer can be resized at runtime; the download_buffer_initial_size_
@@ -109,6 +129,9 @@ class OnlineImage final : public PollingComponent,
 
   uint32_t start_time_{0};
   uint32_t last_data_time_{0};
+  uint32_t last_progress_time_{0};
+  bool streaming_{false};       // The decoder reads the download itself, as it arrives
+  bool stream_started_{false};  // The decoder has read the headers
 };
 
 }  // namespace esphome::online_image

esphome/components/runtime_image/image_decoder.cpp

@@ -2,7 +2,6 @@
 #include "runtime_image.h"
 #include "esphome/core/log.h"
 #include <algorithm>
-#include <cmath>
 
 namespace esphome::runtime_image {
 
@@ -11,19 +10,48 @@ ESPHOME_LOG_TAG(TAG, "image_decoder");
 bool ImageDecoder::set_size(int width, int height) {
   bool success = this->image_->resize(width, height) > 0;
   this->size_valid_ = success;
-  this->x_scale_ = static_cast<double>(this->image_->get_buffer_width()) / width;
-  this->y_scale_ = static_cast<double>(this->image_->get_buffer_height()) / height;
+  this->draw_width_ = width;
+  this->draw_height_ = height;
   return success;
 }
 
+int ImageDecoder::scaled_x_(int x) const {
+  if (this->draw_width_ <= 0)
+    return 0;
+  const uint32_t buffer_width = this->image_->get_buffer_width();
+  return static_cast<int>((static_cast<uint32_t>(x) * buffer_width + this->draw_width_ - 1) / this->draw_width_);
+}
+
+int ImageDecoder::scaled_y_(int y) const {
+  if (this->draw_height_ <= 0)
+    return 0;
+  const uint32_t buffer_height = this->image_->get_buffer_height();
+  return static_cast<int>((static_cast<uint32_t>(y) * buffer_height + this->draw_height_ - 1) / this->draw_height_);
+}
+
 void ImageDecoder::draw(int x, int y, int w, int h, const Color &color) {
   if (!this->size_valid_) {
     return;
   }
-  auto width = std::min(this->image_->get_buffer_width(), static_cast<int>(std::ceil((x + w) * this->x_scale_)));
-  auto height = std::min(this->image_->get_buffer_height(), static_cast<int>(std::ceil((y + h) * this->y_scale_)));
-  for (int i = x * this->x_scale_; i < width; i++) {
-    for (int j = y * this->y_scale_; j < height; j++) {
+  // A source pixel paints the target pixels from ceil(start * scale) up to ceil(end * scale). The spans of neighbouring
+  // pixels meet without overlapping, so when an image is shrunk each target pixel is painted once, by the first
+  // source pixel that reaches it, rather than by every pixel that lands on it. Integer maths: the S3 has no double FPU.
+  const int buffer_width = this->image_->get_buffer_width();
+  const int buffer_height = this->image_->get_buffer_height();
+  int x1 = x;
+  int y1 = y;
+  int x2 = x + w;
+  int y2 = y + h;
+  if (buffer_width != this->draw_width_ || buffer_height != this->draw_height_) {
+    x1 = this->scaled_x_(x);
+    y1 = this->scaled_y_(y);
+    x2 = this->scaled_x_(x + w);
+    y2 = this->scaled_y_(y + h);
+  }
+  x2 = std::min(buffer_width, x2);
+  y2 = std::min(buffer_height, y2);
+  for (int i = x1; i < x2; i++) {
+    for (int j = y1; j < y2; j++) {
       this->image_->draw_pixel(i, j, color);
     }
   }

esphome/components/runtime_image/image_decoder.h

@@ -83,8 +83,8 @@ class ImageDecoder {
     this->expected_size_ = 0;
     this->decoded_bytes_ = 0;
     this->size_valid_ = true;
-    this->x_scale_ = 1.0;
-    this->y_scale_ = 1.0;
+    this->draw_width_ = 0;
+    this->draw_height_ = 0;
   }
 
   /**
@@ -184,8 +184,13 @@ class ImageDecoder {
   uint8_t *image_buffer_() const;
   bool image_is_big_endian_() const;
 
-  double x_scale_ = 1.0;
-  double y_scale_ = 1.0;
+  /// The first buffer column, or row, that source column x, or row y, paints: ceil(x * buffer size / draw size)
+  int scaled_x_(int x) const;
+  int scaled_y_(int y) const;
+
+  // Size of the image as the decoder draws it, which draw() spreads over the buffer
+  int draw_width_ = 0;
+  int draw_height_ = 0;
   RuntimeImage *image_;
   size_t expected_size_ = 0;  // Expected data size (0 if unknown)
   size_t decoded_bytes_ = 0;  // Bytes processed so far

esphome/components/runtime_image/jpeg_decoder.cpp

@@ -31,8 +31,8 @@ bool JpegDecoder::prepare_rgb565_scaling_(int width, int height) {
   const uint32_t target_width = this->image_->get_buffer_width();
   const uint32_t target_height = this->image_->get_buffer_height();
   // Boundary n is the first target pixel source pixel n covers, rounded up. When shrinking, the source
-  // pixel whose span lands on a target pixel paints it, so an 8 to 4 scale keeps columns 0, 2, 4 and 6;
-  // the generic draw() path rounds down and keeps the odd ones instead
+  // pixel whose span lands on a target pixel paints it, so an 8 to 4 scale keeps columns 0, 2, 4 and 6,
+  // as the generic draw() path does
   for (uint32_t x = 0; x <= static_cast<uint32_t>(width); x++) {
     this->x_boundaries_.push_back(static_cast<uint16_t>((x * target_width + width - 1) / width));
   }
@@ -138,7 +138,7 @@ int HOT JpegDecoder::decode(uint8_t *buffer, size_t size) {
   const int err = this->start_();
   if (err != 0)
     return err;
-  if (!this->jpeg_.decode(0, 0, 0))
+  if (!this->jpeg_.decode(0, 0, this->scale_option_()))
     return this->fail_();
   this->decoded_bytes_ = size;
   this->jpeg_.close();
@@ -165,10 +165,28 @@ int JpegDecoder::start_() {
   } else {
     this->jpeg_.setPixelType(RGB8888);
   }
-  if (!this->set_size(this->jpeg_.getWidth(), this->jpeg_.getHeight())) {
+  const int width = this->jpeg_.getWidth();
+  const int height = this->jpeg_.getHeight();
+  if (!this->set_size(width, height)) {
     return DECODE_ERROR_OUT_OF_MEMORY;
   }
-  if (this->direct_rgb565_ && !this->prepare_rgb565_scaling_(this->jpeg_.getWidth(), this->jpeg_.getHeight())) {
+  // JPEGDEC can decode at 1/2, 1/4 or 1/8 size for much less work. Use the smallest size that still has at least as
+  // many pixels as the buffer, so a large image shown small is not decoded in full only to be thrown away.
+  const int buffer_width = this->image_->get_buffer_width();
+  const int buffer_height = this->image_->get_buffer_height();
+  this->scale_ = 1;
+  while (this->scale_ < JPEG_SCALE_EIGHTH && width / (this->scale_ * 2) >= buffer_width &&
+         height / (this->scale_ * 2) >= buffer_height) {
+    this->scale_ *= 2;
+  }
+  const int decoded_width = (width + this->scale_ - 1) / this->scale_;
+  const int decoded_height = (height + this->scale_ - 1) / this->scale_;
+  this->draw_width_ = decoded_width;
+  this->draw_height_ = decoded_height;
+  if (this->scale_ != 1) {
+    ESP_LOGD(TAG, "Decoding at 1/%d size, %d x %d", this->scale_, decoded_width, decoded_height);
+  }
+  if (this->direct_rgb565_ && !this->prepare_rgb565_scaling_(decoded_width, decoded_height)) {
     return DECODE_ERROR_OUT_OF_MEMORY;
   }
   return 0;
@@ -252,7 +270,7 @@ int JpegDecoder::begin_source(DecodeSource *source) {
     this->source_ = nullptr;
     return err;
   }
-  if (!this->jpeg_.decodeBegin(0, 0, 0))
+  if (!this->jpeg_.decodeBegin(0, 0, this->scale_option_()))
     return this->fail_();
   return 0;
 }

esphome/components/runtime_image/jpeg_decoder.h

@@ -31,12 +31,16 @@ class JpegDecoder : public ImageDecoder {
   int HOT decode_step() override;
 
   bool uses_direct_rgb565() const { return this->direct_rgb565_; }
+  /// JPEGDEC decodes the image at 1/get_scale() of its size: 1, 2, 4 or 8
+  int get_scale() const { return this->scale_; }
   void draw_rgb565(int x, int y, int w, int h, const uint8_t *pixels);
 
  protected:
   bool prepare_rgb565_scaling_(int width, int height);
   /// Set up an opened image for decoding. Returns 0, or a DecodeError.
   int start_();
+  /// The JPEGDEC option for scale_: JPEG_SCALE_HALF, _QUARTER and _EIGHTH are the divisors themselves
+  int scale_option_() const { return this->scale_ == 1 ? 0 : this->scale_; }
   /// The DecodeError for a failed read of the source or JPEGDEC's last error, closing the image
   int fail_();
 
@@ -49,6 +53,7 @@ class JpegDecoder : public ImageDecoder {
   FixedVector<uint16_t> y_boundaries_{};
   int source_width_{0};
   int source_height_{0};
+  int scale_{1};                   // JPEGDEC decodes at 1/scale_ of the image size
   DecodeSource *source_{nullptr};  // Set while a begin_source() decode is in progress
   bool direct_rgb565_{false};
   bool source_failed_{false};

esphome/components/runtime_image/runtime_image.cpp

@@ -116,7 +116,9 @@ void RuntimeImage::draw_pixel(int x, int y, const Color &color) {
     }
     case image::IMAGE_TYPE_GRAYSCALE: {
       uint32_t pos = this->get_position_(x, y);
-      auto gray = static_cast<uint8_t>(0.2125 * color.r + 0.7154 * color.g + 0.0721 * color.b);
+      // 0.2125, 0.7154 and 0.0721 in 1/256ths, summing to 256 so white stays 255. Integer maths: the S3 has no
+      // double FPU
+      auto gray = static_cast<uint8_t>((54 * color.r + 183 * color.g + 19 * color.b) >> 8);
       if (this->transparency_ == image::TRANSPARENCY_CHROMA_KEY) {
         if (gray == 1) {
           gray = 0;

tests/components/online_image/common.yaml

@@ -19,6 +19,11 @@ image:
         } else {
           ESP_LOGD("online_image", "Cache miss: fresh download");
         }
+    on_download_started:
+      - logger.log: Download started
+    on_download_progress:
+      lambda: |-
+        ESP_LOGD("online_image", "Downloaded %.0f%% (%zu bytes)", progress, bytes_read);
   - platform: online_image
     id: online_binary_transparent_image
     url: http://www.libpng.org/pub/png/img_png/pnglogo-blk-tiny.png

tests/components/online_image/test_download_end.cpp

@@ -2,6 +2,7 @@
 
 #include <algorithm>
 #include <array>
+#include <cmath>
 #include <cstdint>
 #include <cstring>
 #include <memory>
@@ -27,6 +28,9 @@ class FakeContainer : public http_request::HttpContainer {
   }
 
   int read(uint8_t *buf, size_t max_len) override {
+    this->largest_read = std::max(this->largest_read, max_len);
+    if (this->read_error_)
+      return -1;
     size_t len = std::min(max_len, this->available_ - this->bytes_read_);
     std::memcpy(buf, this->body_.data() + this->bytes_read_, len);
     this->bytes_read_ += len;
@@ -42,13 +46,21 @@ class FakeContainer : public http_request::HttpContainer {
   }
 
   void set_content_length(size_t length) { this->content_length = length; }
+  /// Make every read from now on fail, like a dropped connection
+  void fail_reads() { this->read_error_ = true; }
+  /// Let len more bytes of the body arrive
+  void deliver(size_t len) { this->available_ = std::min(this->body_.size(), this->available_ + len); }
   void add_response_header(const std::string &name, const std::string &value) {
     this->response_headers_.push_back({name, value});
   }
 
+  /// The most bytes any one read() asked for
+  size_t largest_read{0};
+
  protected:
   std::vector<uint8_t> body_;
   size_t available_;
+  bool read_error_{false};
 };
 
 class FakeHttpRequest : public http_request::HttpRequestComponent {
@@ -123,13 +135,173 @@ static constexpr std::array<uint8_t, 69> PNG_1X1{
     0x0C, 0x49, 0x44, 0x41, 0x54, 0x78, 0x9C, 0x63, 0xF8, 0xCF, 0xC0, 0x00, 0x00, 0x03, 0x01, 0x01, 0x00, 0xC9,
     0xFE, 0x92, 0xEF, 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4E, 0x44, 0xAE, 0x42, 0x60, 0x82};
 
+// 8x8 progressive JPEG, 521 bytes
+static const uint8_t JPEG_PROGRESSIVE[] = {
+    0xFF, 0xD8, 0xFF, 0xE0, 0x00, 0x10, 0x4A, 0x46, 0x49, 0x46, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00,
+    0x00, 0xFF, 0xDB, 0x00, 0x43, 0x00, 0x10, 0x0B, 0x0C, 0x0E, 0x0C, 0x0A, 0x10, 0x0E, 0x0D, 0x0E, 0x12, 0x11, 0x10,
+    0x13, 0x18, 0x28, 0x1A, 0x18, 0x16, 0x16, 0x18, 0x31, 0x23, 0x25, 0x1D, 0x28, 0x3A, 0x33, 0x3D, 0x3C, 0x39, 0x33,
+    0x38, 0x37, 0x40, 0x48, 0x5C, 0x4E, 0x40, 0x44, 0x57, 0x45, 0x37, 0x38, 0x50, 0x6D, 0x51, 0x57, 0x5F, 0x62, 0x67,
+    0x68, 0x67, 0x3E, 0x4D, 0x71, 0x79, 0x70, 0x64, 0x78, 0x5C, 0x65, 0x67, 0x63, 0xFF, 0xDB, 0x00, 0x43, 0x01, 0x11,
+    0x12, 0x12, 0x18, 0x15, 0x18, 0x2F, 0x1A, 0x1A, 0x2F, 0x63, 0x42, 0x38, 0x42, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63,
+    0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63,
+    0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63,
+    0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0xFF, 0xC2, 0x00, 0x11, 0x08, 0x00, 0x08, 0x00, 0x08, 0x03, 0x01, 0x22, 0x00,
+    0x02, 0x11, 0x01, 0x03, 0x11, 0x01, 0xFF, 0xC4, 0x00, 0x15, 0x00, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0xFF, 0xC4, 0x00, 0x15, 0x01, 0x01, 0x01, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x05, 0xFF, 0xDA, 0x00, 0x0C, 0x03,
+    0x01, 0x00, 0x02, 0x10, 0x03, 0x10, 0x00, 0x00, 0x01, 0x94, 0x05, 0x3F, 0xFF, 0xC4, 0x00, 0x14, 0x10, 0x01, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xDA, 0x00, 0x08,
+    0x01, 0x01, 0x00, 0x01, 0x05, 0x02, 0x7F, 0xFF, 0xC4, 0x00, 0x14, 0x11, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xDA, 0x00, 0x08, 0x01, 0x03, 0x01, 0x01, 0x3F,
+    0x01, 0x7F, 0xFF, 0xC4, 0x00, 0x14, 0x11, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xDA, 0x00, 0x08, 0x01, 0x02, 0x01, 0x01, 0x3F, 0x01, 0x7F, 0xFF, 0xC4, 0x00,
+    0x14, 0x10, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0xFF, 0xDA, 0x00, 0x08, 0x01, 0x01, 0x00, 0x06, 0x3F, 0x02, 0x7F, 0xFF, 0xC4, 0x00, 0x14, 0x10, 0x01, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xDA, 0x00, 0x08, 0x01,
+    0x01, 0x00, 0x01, 0x3F, 0x21, 0x7F, 0xFF, 0xDA, 0x00, 0x0C, 0x03, 0x01, 0x00, 0x02, 0x00, 0x03, 0x00, 0x00, 0x00,
+    0x10, 0x0B, 0xFF, 0xC4, 0x00, 0x14, 0x11, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xDA, 0x00, 0x08, 0x01, 0x03, 0x01, 0x01, 0x3F, 0x10, 0x7F, 0xFF, 0xC4, 0x00,
+    0x14, 0x11, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0xFF, 0xDA, 0x00, 0x08, 0x01, 0x02, 0x01, 0x01, 0x3F, 0x10, 0x7F, 0xFF, 0xC4, 0x00, 0x14, 0x10, 0x01, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xDA, 0x00, 0x08, 0x01,
+    0x01, 0x00, 0x01, 0x3F, 0x10, 0x7F, 0xFF, 0xD9,
+};
+
+// 48x40 4:2:0 JPEG (quality 95), 2344 bytes: three rows of 16 pixel MCUs, with the scan starting at byte 609
+static const uint8_t JPEG_48X40[] = {
+    0xFF, 0xD8, 0xFF, 0xE0, 0x00, 0x10, 0x4A, 0x46, 0x49, 0x46, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00,
+    0x00, 0xFF, 0xDB, 0x00, 0x43, 0x00, 0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02,
+    0x02, 0x02, 0x04, 0x03, 0x02, 0x02, 0x02, 0x02, 0x05, 0x04, 0x04, 0x03, 0x04, 0x06, 0x05, 0x06, 0x06, 0x06, 0x05,
+    0x06, 0x06, 0x06, 0x07, 0x09, 0x08, 0x06, 0x07, 0x09, 0x07, 0x06, 0x06, 0x08, 0x0B, 0x08, 0x09, 0x0A, 0x0A, 0x0A,
+    0x0A, 0x0A, 0x06, 0x08, 0x0B, 0x0C, 0x0B, 0x0A, 0x0C, 0x09, 0x0A, 0x0A, 0x0A, 0xFF, 0xDB, 0x00, 0x43, 0x01, 0x02,
+    0x02, 0x02, 0x02, 0x02, 0x02, 0x05, 0x03, 0x03, 0x05, 0x0A, 0x07, 0x06, 0x07, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A,
+    0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A,
+    0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A,
+    0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0x0A, 0xFF, 0xC0, 0x00, 0x11, 0x08, 0x00, 0x28, 0x00, 0x30, 0x03, 0x01, 0x22, 0x00,
+    0x02, 0x11, 0x01, 0x03, 0x11, 0x01, 0xFF, 0xC4, 0x00, 0x1F, 0x00, 0x00, 0x01, 0x05, 0x01, 0x01, 0x01, 0x01, 0x01,
+    0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A,
+    0x0B, 0xFF, 0xC4, 0x00, 0xB5, 0x10, 0x00, 0x02, 0x01, 0x03, 0x03, 0x02, 0x04, 0x03, 0x05, 0x05, 0x04, 0x04, 0x00,
+    0x00, 0x01, 0x7D, 0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12, 0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07,
+    0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xA1, 0x08, 0x23, 0x42, 0xB1, 0xC1, 0x15, 0x52, 0xD1, 0xF0, 0x24, 0x33, 0x62,
+    0x72, 0x82, 0x09, 0x0A, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x34, 0x35, 0x36, 0x37,
+    0x38, 0x39, 0x3A, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5A,
+    0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6A, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A, 0x83, 0x84, 0x85,
+    0x86, 0x87, 0x88, 0x89, 0x8A, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9A, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6,
+    0xA7, 0xA8, 0xA9, 0xAA, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7, 0xB8, 0xB9, 0xBA, 0xC2, 0xC3, 0xC4, 0xC5, 0xC6, 0xC7,
+    0xC8, 0xC9, 0xCA, 0xD2, 0xD3, 0xD4, 0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xDA, 0xE1, 0xE2, 0xE3, 0xE4, 0xE5, 0xE6, 0xE7,
+    0xE8, 0xE9, 0xEA, 0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9, 0xFA, 0xFF, 0xC4, 0x00, 0x1F, 0x01, 0x00,
+    0x03, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x02, 0x03,
+    0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0xFF, 0xC4, 0x00, 0xB5, 0x11, 0x00, 0x02, 0x01, 0x02, 0x04, 0x04,
+    0x03, 0x04, 0x07, 0x05, 0x04, 0x04, 0x00, 0x01, 0x02, 0x77, 0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21, 0x31,
+    0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71, 0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91, 0xA1, 0xB1, 0xC1, 0x09,
+    0x23, 0x33, 0x52, 0xF0, 0x15, 0x62, 0x72, 0xD1, 0x0A, 0x16, 0x24, 0x34, 0xE1, 0x25, 0xF1, 0x17, 0x18, 0x19, 0x1A,
+    0x26, 0x27, 0x28, 0x29, 0x2A, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A,
+    0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5A, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6A, 0x73, 0x74, 0x75,
+    0x76, 0x77, 0x78, 0x79, 0x7A, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8A, 0x92, 0x93, 0x94, 0x95, 0x96,
+    0x97, 0x98, 0x99, 0x9A, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7, 0xA8, 0xA9, 0xAA, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7,
+    0xB8, 0xB9, 0xBA, 0xC2, 0xC3, 0xC4, 0xC5, 0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xD2, 0xD3, 0xD4, 0xD5, 0xD6, 0xD7, 0xD8,
+    0xD9, 0xDA, 0xE2, 0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xEA, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9,
+    0xFA, 0xFF, 0xDA, 0x00, 0x0C, 0x03, 0x01, 0x00, 0x02, 0x11, 0x03, 0x11, 0x00, 0x3F, 0x00, 0xFC, 0xAA, 0xB8, 0xB7,
+    0xD3, 0xB5, 0xD8, 0x1E, 0xD6, 0xD1, 0xA5, 0x5B, 0x4B, 0x46, 0x10, 0xC1, 0x06, 0xA1, 0x29, 0x69, 0x25, 0xB7, 0xC2,
+    0xC6, 0x0C, 0x71, 0x26, 0x5E, 0x50, 0x15, 0x5D, 0xB6, 0x9C, 0x9E, 0x00, 0xC1, 0x67, 0x67, 0x4D, 0xCF, 0x84, 0xF7,
+    0x57, 0xA6, 0xDA, 0x08, 0x52, 0xF5, 0xE5, 0xBA, 0xB8, 0x7B, 0x5B, 0x68, 0xEE, 0x2F, 0x66, 0x89, 0xB7, 0xB7, 0x9B,
+    0xE5, 0x9C, 0x23, 0xAA, 0xFE, 0xF7, 0x68, 0x11, 0x9E, 0x5D, 0x18, 0x12, 0x48, 0x56, 0x5C, 0x9F, 0x57, 0xB6, 0xF8,
+    0x33, 0xF0, 0xE2, 0x5B, 0xFB, 0xCF, 0xF4, 0x51, 0x0C, 0xC6, 0x64, 0x30, 0x49, 0x71, 0x7C, 0xE2, 0x16, 0x90, 0x2E,
+    0xF4, 0x72, 0xEA, 0xE0, 0x34, 0x81, 0x77, 0x93, 0x9C, 0x07, 0xC2, 0x93, 0xB9, 0x61, 0xC0, 0xD3, 0xF0, 0x17, 0xC1,
+    0xBF, 0x03, 0xCD, 0xE1, 0xAD, 0x42, 0x3F, 0x0A, 0xD8, 0xC7, 0x2D, 0xAC, 0x36, 0xCB, 0xF6, 0x79, 0x22, 0x69, 0x84,
+    0xC4, 0x93, 0x29, 0x2A, 0x89, 0xB9, 0x00, 0x50, 0x62, 0x7C, 0xFF, 0x00, 0x16, 0xD9, 0x65, 0x00, 0x16, 0x65, 0x07,
+    0xFA, 0x5B, 0x36, 0xE2, 0xAC, 0xBF, 0x2D, 0x55, 0x79, 0x29, 0xB5, 0x26, 0x9B, 0xA9, 0x18, 0xB5, 0x15, 0x36, 0x9B,
+    0x53, 0xD1, 0xCA, 0x10, 0x93, 0x69, 0xB6, 0x94, 0x27, 0x16, 0xAF, 0x19, 0x29, 0xB8, 0xBB, 0x3F, 0x9A, 0xE1, 0x1E,
+    0x2A, 0xCB, 0x9E, 0x79, 0x4A, 0x92, 0x84, 0xDA, 0xD6, 0xED, 0xA4, 0xED, 0x7A, 0x72, 0xB5, 0xAC, 0xF6, 0xEB, 0xAD,
+    0xD5, 0x97, 0x91, 0xC9, 0x4D, 0xA4, 0xE9, 0xD7, 0x56, 0x45, 0x66, 0xD3, 0x9D, 0x85, 0xB1, 0x86, 0x59, 0x7E, 0xD9,
+    0x7E, 0xA0, 0xE0, 0xA8, 0x02, 0x17, 0x02, 0x3C, 0x36, 0x59, 0x18, 0xE2, 0x42, 0x1D, 0x40, 0x56, 0x0A, 0x77, 0x30,
+    0xAE, 0xFA, 0x56, 0xD4, 0xA4, 0x8A, 0xD9, 0xAD, 0xD6, 0x38, 0x1D, 0x7F, 0x77, 0x77, 0x1C, 0xB2, 0x4C, 0x22, 0x8C,
+    0x2B, 0xF3, 0x14, 0x64, 0x45, 0x85, 0x52, 0x47, 0x92, 0x7E, 0xF2, 0x0F, 0x34, 0x1D, 0xBC, 0x56, 0xDE, 0x85, 0xF0,
+    0x4B, 0xE1, 0x0A, 0xE9, 0xB0, 0xDB, 0x2D, 0x8C, 0x4C, 0xCD, 0x74, 0xF1, 0x42, 0x96, 0x93, 0xCF, 0xF6, 0x54, 0x0C,
+    0xB3, 0x44, 0x03, 0xAA, 0x6C, 0x49, 0x10, 0x87, 0x00, 0x88, 0xC2, 0xEE, 0x66, 0x6F, 0x9B, 0xAB, 0x57, 0xA4, 0x68,
+    0xDF, 0x0A, 0x3E, 0x1B, 0xDA, 0xE9, 0xDF, 0xD9, 0x96, 0xFE, 0x03, 0xB2, 0x8E, 0xD9, 0x8A, 0xDD, 0xC1, 0x77, 0x14,
+    0x97, 0x50, 0x2E, 0xE3, 0x20, 0x62, 0xA0, 0x33, 0x0C, 0xC6, 0x58, 0x48, 0x36, 0x6D, 0xC1, 0x20, 0xA2, 0x2B, 0x00,
+    0xB5, 0xF1, 0x99, 0xCF, 0x19, 0x65, 0x79, 0xAD, 0x0C, 0x3C, 0x2B, 0x61, 0xF9, 0x28, 0xD6, 0x52, 0x97, 0x35, 0x95,
+    0xD4, 0x61, 0x28, 0x5B, 0x99, 0xB8, 0xA9, 0xA9, 0x47, 0xD9, 0x3A, 0x69, 0xA9, 0xC6, 0x51, 0x52, 0x6A, 0x0D, 0x4A,
+    0x74, 0xA9, 0xC3, 0xFA, 0x7F, 0xC3, 0xFE, 0x25, 0xC1, 0x4E, 0xAE, 0x26, 0x2E, 0x13, 0x71, 0x5C, 0x8D, 0xFB, 0xB1,
+    0xD6, 0xEA, 0x6F, 0xF9, 0xAF, 0xBE, 0xB7, 0x4B, 0x55, 0x1D, 0x75, 0x4C, 0xF3, 0xDF, 0x05, 0xD9, 0xF8, 0x7B, 0xC3,
+    0xBA, 0xB5, 0xF1, 0xBC, 0x8D, 0x63, 0xDF, 0x1C, 0x32, 0x88, 0x1A, 0xF3, 0x74, 0x73, 0x89, 0x15, 0xC4, 0x8A, 0x25,
+    0x66, 0xDC, 0xAA, 0x98, 0x60, 0x06, 0x7F, 0xBD, 0xF2, 0x81, 0xF3, 0x36, 0xFE, 0x9D, 0xAF, 0x78, 0x8F, 0x54, 0xD3,
+    0xAD, 0xA6, 0x9E, 0xC5, 0xE5, 0x9C, 0x96, 0xDC, 0xB7, 0xE8, 0x84, 0x47, 0xFB, 0xB4, 0x54, 0x42, 0x0F, 0x03, 0xF8,
+    0xD7, 0xE5, 0x39, 0x60, 0xF8, 0x04, 0x79, 0x7B, 0xE3, 0xF4, 0x9F, 0x85, 0x5F, 0x08, 0xBE, 0x0D, 0x2C, 0x57, 0xCE,
+    0x6C, 0xA5, 0x2B, 0xA8, 0x08, 0x20, 0x82, 0x04, 0xB9, 0xB8, 0x82, 0x43, 0x28, 0x72, 0x55, 0xD5, 0x83, 0xB9, 0x05,
+    0xC2, 0x44, 0x55, 0x77, 0x8C, 0xFC, 0xEC, 0xD8, 0xCB, 0xE7, 0xBE, 0x9B, 0xE0, 0x5F, 0xC3, 0x9D, 0x32, 0xD4, 0x45,
+    0x26, 0x8B, 0x2C, 0x93, 0xC0, 0xF3, 0x95, 0x49, 0xEE, 0x2E, 0x0C, 0x26, 0x26, 0x31, 0xC9, 0xF3, 0xED, 0x95, 0x96,
+    0x32, 0xEC, 0x10, 0xE1, 0xB8, 0x60, 0x3A, 0x90, 0x1B, 0x3F, 0x9E, 0x66, 0x58, 0xFC, 0x14, 0x31, 0x15, 0xFD, 0x9C,
+    0x79, 0x57, 0x3A, 0x92, 0x84, 0x1C, 0x3D, 0xC9, 0xCD, 0x27, 0x6D, 0x12, 0xE5, 0xE7, 0xA6, 0xD5, 0x4D, 0x64, 0x93,
+    0xD1, 0x45, 0xC6, 0xAD, 0xE7, 0x2F, 0xE9, 0xEE, 0x17, 0xE3, 0x0C, 0x0A, 0xE1, 0x9C, 0x37, 0x34, 0x67, 0x2B, 0x73,
+    0x2B, 0xB4, 0xBA, 0x49, 0xF4, 0x72, 0x57, 0x51, 0xDD, 0x24, 0x9B, 0x5A, 0x36, 0x9A, 0x49, 0x1E, 0x15, 0xA7, 0x7E,
+    0xCE, 0xF6, 0x89, 0x6A, 0x96, 0x43, 0x55, 0xB5, 0xB3, 0xB6, 0xB8, 0x96, 0x2B, 0x9B, 0x78, 0xA0, 0xB4, 0x9E, 0xE5,
+    0x61, 0x90, 0xE0, 0xC2, 0xEC, 0x61, 0x91, 0x47, 0xCC, 0xDB, 0xF1, 0x80, 0xC0, 0x98, 0xD4, 0xE5, 0xDC, 0x64, 0xEC,
+    0x7C, 0x29, 0xFD, 0x98, 0x6C, 0xAF, 0xEC, 0xF5, 0x76, 0xB7, 0xF1, 0x36, 0x9A, 0x5D, 0x6F, 0x96, 0xE1, 0x74, 0xB5,
+    0xD3, 0x44, 0x91, 0xA8, 0x45, 0x0C, 0xE2, 0x3D, 0xAC, 0x85, 0xF9, 0x3B, 0x5B, 0x19, 0x8A, 0x43, 0x1F, 0xCA, 0x50,
+    0x9D, 0x87, 0xD2, 0x0F, 0xC2, 0x1F, 0x89, 0x4F, 0x6D, 0x04, 0x0F, 0xE1, 0x61, 0xAA, 0xEE, 0xB4, 0x8E, 0x56, 0xFB,
+    0x06, 0xAF, 0x04, 0xF3, 0x40, 0x9B, 0x55, 0x4E, 0xCB, 0x66, 0x91, 0xCB, 0x18, 0xC2, 0x88, 0xB6, 0xB1, 0x65, 0x60,
+    0xA4, 0x6E, 0xDC, 0xA4, 0x9E, 0xAF, 0xE1, 0xBF, 0xC2, 0x2F, 0x89, 0xA9, 0xE1, 0xFB, 0x8D, 0x6E, 0xC2, 0x3B, 0x4B,
+    0x30, 0xD7, 0x60, 0xDA, 0x41, 0x2D, 0xCC, 0x6C, 0x2E, 0x49, 0xF3, 0x1E, 0x42, 0x19, 0x5D, 0x58, 0x3C, 0x8A, 0x81,
+    0x82, 0xB8, 0x0C, 0xC9, 0xF2, 0xE5, 0x8F, 0x03, 0x8F, 0x36, 0xE3, 0x8A, 0x98, 0xCC, 0x14, 0xAB, 0x62, 0x2B, 0xC2,
+    0x34, 0xA2, 0xA5, 0x78, 0x37, 0x42, 0x12, 0x70, 0x8C, 0x62, 0xD2, 0x6D, 0x72, 0x7B, 0xAF, 0x9B, 0xDD, 0xFD, 0xE5,
+    0x4E, 0x79, 0x49, 0x45, 0x73, 0xA9, 0x72, 0x2F, 0xF0, 0x73, 0x83, 0xF8, 0xCE, 0xB4, 0x33, 0xE8, 0x3F, 0xAE, 0x42,
+    0xF7, 0x76, 0xB3, 0x83, 0x57, 0xE5, 0x95, 0xBE, 0xCE, 0x8F, 0x7B, 0xDE, 0xD7, 0x4B, 0x6B, 0x9C, 0x1E, 0x8D, 0xF0,
+    0x56, 0x7B, 0xDD, 0x26, 0x34, 0x5F, 0x1F, 0xDB, 0x9D, 0x37, 0x53, 0xB8, 0x96, 0xED, 0xA0, 0x16, 0xB1, 0xC9, 0x2C,
+    0x8B, 0xF2, 0x26, 0x58, 0x89, 0x37, 0xEE, 0x04, 0xB2, 0x97, 0x54, 0x2D, 0x88, 0xC0, 0x60, 0x0B, 0x03, 0x5E, 0x9B,
+    0x67, 0xFB, 0x36, 0xE9, 0x31, 0x2D, 0x9C, 0x37, 0x9E, 0x32, 0x84, 0x5D, 0x2C, 0x4A, 0xD6, 0xAD, 0x73, 0x63, 0x28,
+    0x36, 0xAA, 0x53, 0xF7, 0x90, 0x29, 0x8E, 0x5C, 0x92, 0xBE, 0x41, 0xDC, 0xC0, 0xB3, 0x2B, 0x46, 0x32, 0x4B, 0x96,
+    0x35, 0xAD, 0x1F, 0xC2, 0xDF, 0x89, 0x17, 0xF6, 0xB6, 0xFA, 0xB5, 0xED, 0xB8, 0xB7, 0x8E, 0x78, 0x66, 0x96, 0x09,
+    0x6C, 0x6E, 0x23, 0x32, 0x28, 0x08, 0xE8, 0xF2, 0xBA, 0xF9, 0x86, 0x48, 0xC0, 0x68, 0xFE, 0x63, 0xC8, 0x23, 0x82,
+    0xCC, 0xA5, 0x4A, 0xFA, 0x66, 0x8F, 0xF0, 0x37, 0xE2, 0x6D, 0xE5, 0xC9, 0x3A, 0x87, 0x86, 0xB4, 0xFB, 0x28, 0xAE,
+    0x61, 0x0F, 0x0B, 0x59, 0xDF, 0xC0, 0xD1, 0xAC, 0xE0, 0x24, 0x41, 0x42, 0xC4, 0x49, 0x1B, 0x10, 0x21, 0x50, 0xC0,
+    0x09, 0x11, 0x8B, 0xEE, 0x6E, 0x71, 0xE2, 0xE2, 0x78, 0xBB, 0x33, 0xFA, 0xC5, 0x1A, 0xB4, 0xEA, 0xC6, 0x74, 0xD2,
+    0x8C, 0x24, 0xA5, 0x2A, 0x3C, 0xB5, 0x2E, 0xB9, 0x9B, 0x71, 0x97, 0x34, 0xE0, 0xAA, 0x54, 0x93, 0x71, 0x56, 0x49,
+    0xB9, 0xC6, 0x4E, 0x9A, 0x9B, 0xD3, 0xFA, 0x7F, 0x81, 0xB8, 0xD6, 0xAC, 0xDD, 0x6F, 0x65, 0x8D, 0x82, 0x77, 0x85,
+    0x95, 0xE1, 0x7D, 0x1C, 0xD2, 0x8B, 0x7A, 0x27, 0xA2, 0xF4, 0xED, 0xEE, 0x9E, 0x67, 0xE0, 0x8F, 0x81, 0x37, 0xBA,
+    0xEF, 0x87, 0x67, 0xBF, 0x8F, 0xC4, 0xD2, 0xDD, 0x4F, 0x05, 0xA8, 0x61, 0x7B, 0x1E, 0x9E, 0xE1, 0x8C, 0xEA, 0xF3,
+    0x18, 0x99, 0xA3, 0xDE, 0x76, 0x66, 0x36, 0x2A, 0x30, 0xFB, 0x9B, 0x0F, 0xC3, 0x1C, 0xA3, 0x76, 0x4B, 0xFB, 0x3B,
+    0xE8, 0xBA, 0x66, 0xBF, 0x0E, 0x93, 0xFD, 0xAB, 0x23, 0xD9, 0xA5, 0xCE, 0x62, 0xF3, 0x34, 0xEB, 0x7F, 0x29, 0x0A,
+    0xA7, 0x04, 0x48, 0xF2, 0x79, 0x82, 0x42, 0x1D, 0x46, 0x4B, 0xA9, 0x1B, 0xD1, 0xBE, 0x52, 0x54, 0xD7, 0xA8, 0xF8,
+    0x33, 0xE1, 0xAF, 0xC4, 0xA8, 0x24, 0xD6, 0x6D, 0xED, 0xBC, 0x0A, 0xD3, 0x5A, 0x5C, 0xC4, 0xDF, 0x64, 0x17, 0x97,
+    0x36, 0xF0, 0x65, 0x52, 0x39, 0xD4, 0x23, 0x22, 0x9D, 0xD8, 0x64, 0x83, 0x04, 0x85, 0x38, 0xEF, 0xB8, 0x49, 0x91,
+    0xBB, 0xFF, 0x00, 0x0A, 0xDF, 0xE3, 0x77, 0x84, 0xAC, 0xD3, 0x4A, 0xBC, 0xF0, 0x3A, 0x5A, 0x5B, 0x4F, 0x72, 0x5E,
+    0xD7, 0x53, 0x8E, 0xE2, 0x12, 0x6D, 0xC6, 0x40, 0x20, 0x47, 0xE6, 0x3E, 0x71, 0x26, 0x70, 0x24, 0xE4, 0xB4, 0x63,
+    0x2A, 0xC0, 0xE0, 0x7E, 0x71, 0x98, 0x71, 0x35, 0x5C, 0x4E, 0x69, 0x5A, 0xBD, 0x7C, 0x7A, 0x9C, 0xE3, 0xC9, 0xCF,
+    0x38, 0x46, 0x8D, 0xA4, 0xDC, 0x63, 0x38, 0x4A, 0xE9, 0xED, 0x5A, 0x4E, 0x4A, 0x6D, 0xF3, 0xCA, 0x2D, 0xB9, 0x4D,
+    0xD3, 0x77, 0x8C, 0x7F, 0xA8, 0xF8, 0x53, 0x8D, 0x31, 0x32, 0xC8, 0xA9, 0xDB, 0x15, 0x04, 0x9F, 0xB4, 0xD2, 0xF4,
+    0xD3, 0xF8, 0xA5, 0x77, 0xCD, 0xB3, 0x49, 0x6C, 0xB4, 0xEA, 0x97, 0x46, 0x78, 0x45, 0xC4, 0x16, 0x5A, 0xDD, 0xA5,
+    0xA6, 0x8D, 0xA7, 0xEA, 0x77, 0x4A, 0x54, 0x47, 0x3C, 0x31, 0x41, 0x20, 0x06, 0x68, 0x00, 0x9A, 0x4F, 0x2A, 0x40,
+    0x5D, 0x5F, 0x69, 0xF3, 0x15, 0xCB, 0x32, 0x96, 0xDC, 0xC0, 0x90, 0xA5, 0xF0, 0xBD, 0xAF, 0xC3, 0x96, 0x83, 0x51,
+    0xB8, 0xD6, 0xA7, 0x48, 0xD2, 0xE8, 0x2B, 0x2C, 0x2D, 0x6B, 0xF6, 0xA4, 0x55, 0x8E, 0x45, 0x5F, 0xBA, 0x54, 0x2A,
+    0x36, 0x77, 0x12, 0x72, 0xE5, 0x9C, 0x14, 0x3B, 0x63, 0x6C, 0x62, 0x8A, 0x2B, 0xDE, 0xCD, 0x70, 0x74, 0xA7, 0x92,
+    0xE2, 0x31, 0x35, 0x2D, 0x29, 0x54, 0xBB, 0x97, 0xBB, 0x18, 0xF3, 0x38, 0x52, 0xA5, 0x38, 0xDF, 0x92, 0x31, 0x7E,
+    0xEB, 0x9B, 0x6A, 0xCD, 0x6B, 0xEF, 0x7C, 0x6E, 0x52, 0x7F, 0xE1, 0xF7, 0x0E, 0x54, 0x96, 0x1B, 0x3D, 0x52, 0x86,
+    0xF0, 0x73, 0x4B, 0xEE, 0x92, 0xD6, 0xD6, 0xBF, 0xC2, 0x8D, 0x9F, 0x0B, 0xDE, 0xEB, 0xF3, 0x69, 0x6B, 0x06, 0x9B,
+    0xA9, 0x5B, 0xE9, 0xF6, 0x6F, 0x76, 0x1E, 0x45, 0x8E, 0xE1, 0x54, 0xC8, 0xCD, 0xF3, 0x28, 0x8B, 0x1C, 0x9E, 0x25,
+    0x55, 0xDA, 0xA5, 0x58, 0x80, 0xCA, 0x46, 0x42, 0xA8, 0xF4, 0x1B, 0xEB, 0xBB, 0xBB, 0x8B, 0x69, 0xAF, 0xA5, 0x8E,
+    0xD0, 0x49, 0x25, 0x9C, 0x37, 0x73, 0xE9, 0xD7, 0xF2, 0x14, 0x8E, 0x55, 0x91, 0x64, 0x90, 0x46, 0xA8, 0xF9, 0x50,
+    0x57, 0x73, 0x2E, 0xE0, 0x55, 0xF6, 0x87, 0x45, 0x20, 0x2E, 0xC7, 0x28, 0xAF, 0xCD, 0x78, 0xA6, 0xA5, 0x5C, 0x26,
+    0x33, 0x01, 0x35, 0x2E, 0x67, 0x52, 0x35, 0xA0, 0xEE, 0x93, 0x56, 0x70, 0x4F, 0x48, 0xDB, 0x95, 0x6B, 0x76, 0xF4,
+    0xB4, 0xA5, 0x27, 0x29, 0x29, 0x35, 0x16, 0xBF, 0xA8, 0x7C, 0x3E, 0x92, 0xF6, 0x98, 0xA8, 0x5B, 0x4B, 0xC5, 0xDB,
+    0x5E, 0x8E, 0x4F, 0x7D, 0xFA, 0xDB, 0x57, 0xB2, 0x56, 0xD6, 0xED, 0xF7, 0x3E, 0x10, 0xB2, 0x82, 0xF6, 0xC2, 0xF2,
+    0xF3, 0x4E, 0xD4, 0xAF, 0xEE, 0x5A, 0xCA, 0xCE, 0xD2, 0xF1, 0xA7, 0xB8, 0x9D, 0xD4, 0x42, 0x8C, 0xF2, 0x3C, 0x8E,
+    0x42, 0x02, 0x24, 0xFD, 0xDA, 0x96, 0x60, 0xAD, 0xB0, 0xC9, 0x0E, 0x00, 0xC8, 0xC8, 0xEA, 0xEE, 0x12, 0x7B, 0x09,
+    0x6C, 0x6E, 0xCE, 0xA2, 0x0B, 0xAA, 0x32, 0xD9, 0xB9, 0x49, 0x66, 0xDF, 0x74, 0xCC, 0x31, 0x1B, 0xE4, 0xE6, 0x63,
+    0xF2, 0x91, 0x95, 0x42, 0x15, 0x8B, 0x7D, 0xE0, 0xAC, 0xB4, 0x51, 0x5F, 0x33, 0x3A, 0xD8, 0x8C, 0x46, 0x7A, 0x9C,
+    0xA6, 0xD7, 0x2C, 0x13, 0x49, 0x25, 0x6E, 0x6A, 0x73, 0xE4, 0x84, 0x9E, 0x9A, 0xC9, 0x29, 0x24, 0x9E, 0xE9, 0x42,
+    0x11, 0x8D, 0xA2, 0x9C, 0x5F, 0xF5, 0x37, 0x0D, 0x36, 0xF8, 0x7E, 0x9A, 0xEC, 0xE5, 0xE5, 0x7E, 0x67, 0x77, 0x7B,
+    0x7A, 0xBF, 0x5E, 0xB7, 0x3F, 0xFF, 0xD9,
+};
+
 static void set_loop_time(uint32_t now) { LoopBlockingGuard clock(nullptr, LOG_STR("test"), now); }
 
 class OnlineImageDownloadEnd : public ::testing::Test {
  protected:
-  std::unique_ptr<OnlineImage> make_image_(runtime_image::ImageFormat format) {
+  std::unique_ptr<OnlineImage> make_image_(runtime_image::ImageFormat format, uint32_t buffer_size = 256) {
     auto img = std::make_unique<OnlineImage>("http://example.com/image", 0, 0, format, image::IMAGE_TYPE_RGB,
-                                             image::TRANSPARENCY_OPAQUE, nullptr, 256);
+                                             image::TRANSPARENCY_OPAQUE, nullptr, buffer_size);
     img->set_parent(&this->http_);
     return img;
   }
@@ -286,4 +458,294 @@ TEST_F(OnlineImageDownloadEnd, JpegBufferAllocationFailureReportsError) {
   EXPECT_EQ(this->finished_, 0);
 }
 
+// The JPEG decoded with all of it in memory at once, to compare the downloaded images with
+static std::vector<uint8_t> reference_jpeg_pixels() {
+  runtime_image::RuntimeImage ref(runtime_image::JPEG, image::IMAGE_TYPE_RGB, image::TRANSPARENCY_OPAQUE);
+  std::vector<uint8_t> data(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40));
+  EXPECT_TRUE(ref.begin_decode(data.size()));
+  EXPECT_EQ(ref.feed_data(data.data(), data.size()), static_cast<int>(data.size()));
+  EXPECT_TRUE(ref.end_decode());
+  return std::vector<uint8_t>(ref.get_data_start(), ref.get_data_start() + ref.get_width_stride() * ref.get_height());
+}
+
+static std::vector<uint8_t> image_pixels(OnlineImage &image) {
+  return std::vector<uint8_t>(image.get_data_start(),
+                              image.get_data_start() + image.get_width_stride() * image.get_height());
+}
+
+// A JPEG of known size is decoded as it arrives, so a buffer smaller than the file only has to hold the headers
+TEST_F(OnlineImageDownloadEnd, JpegDecodesThroughASmallBuffer) {
+  auto image = this->make_image_(runtime_image::JPEG, 1024);
+  // Bytes after the image are never needed. Waiting for the whole file before decoding would read them all.
+  std::vector<uint8_t> body(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40));
+  body.resize(body.size() + 8192, 0);
+  auto container = std::make_shared<FakeContainer>(body, body.size(), false);
+  container->add_response_header("etag", "\"abc\"");
+  this->start_(*image, container);
+
+  for (int i = 0; i < 100 && this->finished_ + this->errors_ == 0; i++)
+    image->loop();
+
+  ASSERT_EQ(this->finished_, 1);
+  EXPECT_LT(container->get_bytes_read(), body.size()) << "the image was not decoded as it arrived";
+  EXPECT_EQ(this->errors_, 0);
+  ASSERT_EQ(image->get_width(), 48);
+  ASSERT_EQ(image->get_height(), 40);
+  EXPECT_EQ(image_pixels(*image), reference_jpeg_pixels());
+
+  // A complete image is cached
+  this->http_.next = std::make_shared<FakeContainer>(std::vector<uint8_t>{}, 0, false);
+  image->update();
+  EXPECT_TRUE(this->http_.sent_header("if-none-match"));
+}
+
+// A read() waits for every byte it asks for, so a large buffer is filled a little at a time rather than in one
+// read that blocks the loop until the whole buffer has arrived
+TEST_F(OnlineImageDownloadEnd, JpegReadsInSmallPiecesWithALargeBuffer) {
+  auto image = this->make_image_(runtime_image::JPEG, 65536);
+  auto container =
+      std::make_shared<FakeContainer>(std::vector<uint8_t>(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40)), 0, false);
+  this->start_(*image, container);
+
+  for (int i = 0; i < 100 && this->finished_ + this->errors_ == 0; i++) {
+    container->deliver(sizeof(JPEG_48X40));
+    image->loop();
+  }
+
+  ASSERT_EQ(this->finished_, 1);
+  EXPECT_EQ(this->errors_, 0);
+  EXPECT_LE(container->largest_read, READ_CHUNK);
+  EXPECT_EQ(image_pixels(*image), reference_jpeg_pixels());
+}
+
+// A downloaded PNG is read a little at a time too
+TEST_F(OnlineImageDownloadEnd, PngReadsInSmallPiecesWithALargeBuffer) {
+  auto image = this->make_image_(runtime_image::PNG, 65536);
+  std::vector<uint8_t> png(PNG_1X1.begin(), PNG_1X1.end());
+  auto container = std::make_shared<FakeContainer>(png, png.size(), false);
+  this->start_(*image, container);
+
+  for (int i = 0; i < 100 && this->finished_ + this->errors_ == 0; i++)
+    image->loop();
+
+  ASSERT_EQ(this->finished_, 1);
+  EXPECT_EQ(this->errors_, 0);
+  EXPECT_LE(container->largest_read, READ_CHUNK);
+}
+
+// A slow link: the decoder waits part way through the image for the rest to arrive
+TEST_F(OnlineImageDownloadEnd, JpegWaitsForASlowDownload) {
+  auto image = this->make_image_(runtime_image::JPEG, 1024);
+  auto container =
+      std::make_shared<FakeContainer>(std::vector<uint8_t>(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40)), 1024, false);
+  this->start_(*image, container);
+
+  int passes = 0;
+  for (; passes < 1000 && this->finished_ + this->errors_ == 0; passes++) {
+    image->loop();
+    if (passes == 5) {
+      EXPECT_EQ(this->finished_, 0) << "the image cannot be finished before the rest of it arrives";
+    }
+    container->deliver(40);
+  }
+
+  ASSERT_EQ(this->finished_, 1);
+  EXPECT_EQ(this->errors_, 0);
+  EXPECT_GT(passes, 10);
+  EXPECT_EQ(image_pixels(*image), reference_jpeg_pixels());
+}
+
+// A download that stops part way through times out rather than waiting for ever
+TEST_F(OnlineImageDownloadEnd, JpegDownloadThatStopsTimesOut) {
+  auto image = this->make_image_(runtime_image::JPEG, 1024);
+  auto container =
+      std::make_shared<FakeContainer>(std::vector<uint8_t>(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40)), 1500, false);
+  set_loop_time(1000);
+  this->start_(*image, container);
+
+  for (int i = 0; i < 10; i++)
+    image->loop();
+  EXPECT_EQ(this->errors_, 0) << "still within the timeout";
+
+  set_loop_time(1000 + this->http_.get_timeout());
+  image->loop();
+  EXPECT_EQ(this->errors_, 1);
+  EXPECT_EQ(this->finished_, 0);
+}
+
+// Headers that do not fit the download buffer cannot be read as the image arrives, so the whole image is
+// downloaded first, keeping the bytes already read
+TEST_F(OnlineImageDownloadEnd, JpegHeadersLargerThanTheBufferDownloadTheWholeImage) {
+  auto image = this->make_image_(runtime_image::JPEG, 256);
+  auto container = std::make_shared<FakeContainer>(std::vector<uint8_t>(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40)),
+                                                   sizeof(JPEG_48X40), false);
+  this->start_(*image, container);
+
+  for (int i = 0; i < 100 && this->finished_ + this->errors_ == 0; i++) {
+    image->loop();
+    container->deliver(256);
+  }
+
+  ASSERT_EQ(this->finished_, 1);
+  EXPECT_EQ(this->errors_, 0);
+  EXPECT_EQ(container->get_bytes_read(), sizeof(JPEG_48X40));
+  EXPECT_EQ(image_pixels(*image), reference_jpeg_pixels());
+}
+
+// The pass that opens the image does not decode any of it
+TEST_F(OnlineImageDownloadEnd, JpegOpensInAPassOfItsOwn) {
+  auto image = this->make_image_(runtime_image::JPEG, 1024);
+  auto container = std::make_shared<FakeContainer>(std::vector<uint8_t>(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40)),
+                                                   sizeof(JPEG_48X40), false);
+  this->start_(*image, container);
+
+  image->loop();
+  EXPECT_EQ(this->finished_ + this->errors_, 0);
+  for (int i = 0; i < 100 && this->finished_ + this->errors_ == 0; i++)
+    image->loop();
+  EXPECT_EQ(this->finished_, 1);
+}
+
+// A progressive JPEG is refused while it downloads, without blaming the buffer size
+TEST_F(OnlineImageDownloadEnd, JpegProgressiveReportsError) {
+  auto image = this->make_image_(runtime_image::JPEG, 256);
+  std::vector<uint8_t> body(JPEG_PROGRESSIVE, JPEG_PROGRESSIVE + sizeof(JPEG_PROGRESSIVE));
+  auto container = std::make_shared<FakeContainer>(body, 256, false);
+  this->start_(*image, container);
+
+  for (int i = 0; i < 10 && this->finished_ + this->errors_ == 0; i++)
+    image->loop();
+
+  EXPECT_EQ(this->errors_, 1);
+  EXPECT_EQ(this->finished_, 0);
+}
+
+// on_download_started fires once the server has accepted the request, before the first progress report, and not
+// for a response that has no image to download
+TEST_F(OnlineImageDownloadEnd, StartedFiresOnlyWhenTheDownloadBegins) {
+  auto image = this->make_image_(runtime_image::JPEG, 1024);
+  std::vector<std::string> events;
+  image->add_on_download_started_callback([&events]() { events.emplace_back("started"); });
+  image->add_on_progress_callback([&events](float, size_t) { events.emplace_back("progress"); });
+  this->start_(*image,
+               std::make_shared<FakeContainer>(std::vector<uint8_t>(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40)),
+                                               sizeof(JPEG_48X40), false));
+  ASSERT_GE(events.size(), 2u);
+  EXPECT_EQ(events[0], "started");
+  EXPECT_EQ(events[1], "progress");
+  for (int i = 0; i < 100 && this->finished_ + this->errors_ == 0; i++)
+    image->loop();
+  EXPECT_EQ(std::count(events.begin(), events.end(), std::string("started")), 1);
+
+  for (int status : {304, 404}) {
+    events.clear();
+    auto container = std::make_shared<FakeContainer>(std::vector<uint8_t>{}, 0, false);
+    container->status_code = status;
+    this->http_.next = container;
+    image->update();
+    EXPECT_TRUE(events.empty()) << "HTTP " << status;
+  }
+}
+
+// Progress starts at 0, is reported at most every 100 ms, and always reaches 100%
+TEST_F(OnlineImageDownloadEnd, ProgressIsReportedAsTheImageDownloads) {
+  auto image = this->make_image_(runtime_image::JPEG, 1024);
+  std::vector<float> reports;
+  image->add_on_progress_callback([&reports](float progress, size_t) { reports.push_back(progress); });
+  auto container =
+      std::make_shared<FakeContainer>(std::vector<uint8_t>(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40)), 100, false);
+  uint32_t now = 1000;
+  set_loop_time(now);
+  this->start_(*image, container);
+  ASSERT_EQ(reports.size(), 1u);
+  EXPECT_EQ(reports[0], 0.0f);
+
+  int passes = 0;
+  for (; passes < 1000 && this->finished_ + this->errors_ == 0; passes++) {
+    now += 50;
+    set_loop_time(now);
+    container->deliver(100);
+    image->loop();
+  }
+
+  ASSERT_EQ(this->finished_, 1);
+  EXPECT_EQ(reports.back(), 100.0f);
+  EXPECT_TRUE(std::is_sorted(reports.begin(), reports.end()));
+  // A report every 100 ms of a 50 ms loop, plus the start and the end
+  EXPECT_LE(reports.size(), static_cast<size_t>(passes / 2 + 2));
+  EXPECT_GT(reports.size(), 3u);
+}
+
+// Without a Content-Length the percentage is unknown, but the bytes read are still reported
+TEST_F(OnlineImageDownloadEnd, ProgressOfAChunkedDownloadHasNoPercentage) {
+  auto image = this->make_image_(runtime_image::PNG);
+  std::vector<std::pair<float, size_t>> reports;
+  image->add_on_progress_callback(
+      [&reports](float progress, size_t bytes_read) { reports.emplace_back(progress, bytes_read); });
+  auto container =
+      std::make_shared<FakeContainer>(std::vector<uint8_t>(PNG_1X1.begin(), PNG_1X1.end()), PNG_1X1.size(), true);
+  set_loop_time(1000);
+  this->start_(*image, container);
+  set_loop_time(2000);
+  for (int i = 0; i < 10 && this->finished_ + this->errors_ == 0; i++)
+    image->loop();
+
+  ASSERT_GE(reports.size(), 2u);
+  EXPECT_TRUE(std::isnan(reports.back().first));
+  EXPECT_EQ(reports.back().second, PNG_1X1.size());
+}
+
+// Scan data that cannot be decoded fails the download part way through
+TEST_F(OnlineImageDownloadEnd, JpegDecodeErrorFailsTheDownload) {
+  auto image = this->make_image_(runtime_image::JPEG, 1024);
+  std::vector<uint8_t> body(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40));
+  std::fill(body.begin() + 700, body.end() - 2, 0xFE);
+  auto container = std::make_shared<FakeContainer>(body, 1024, false);
+  this->start_(*image, container);
+
+  for (int i = 0; i < 100 && this->finished_ + this->errors_ == 0; i++) {
+    image->loop();
+    container->deliver(256);
+  }
+
+  EXPECT_EQ(this->errors_, 1);
+  EXPECT_EQ(this->finished_, 0);
+}
+
+// A read that fails part way through the download ends it with an error
+TEST_F(OnlineImageDownloadEnd, JpegReadErrorFailsTheDownload) {
+  auto image = this->make_image_(runtime_image::JPEG, 1024);
+  auto container =
+      std::make_shared<FakeContainer>(std::vector<uint8_t>(JPEG_48X40, JPEG_48X40 + sizeof(JPEG_48X40)), 1024, false);
+  this->start_(*image, container);
+  for (int i = 0; i < 5; i++)
+    image->loop();
+  ASSERT_EQ(this->errors_, 0);
+
+  container->fail_reads();
+  image->loop();
+  EXPECT_EQ(this->errors_, 1);
+  EXPECT_EQ(this->finished_, 0);
+}
+
+TEST(DownloadBufferGrow, KeepsTheUnreadData) {
+  DownloadBuffer buffer(16);
+  std::memcpy(buffer.append(), "abcdef", 6);
+  buffer.write(6);
+  buffer.read(2);
+
+  ASSERT_TRUE(buffer.grow(64));
+  EXPECT_EQ(buffer.size(), 64u);
+  ASSERT_EQ(buffer.unread(), 4u);
+  EXPECT_EQ(std::memcmp(buffer.data(), "cdef", 4), 0);
+
+  // A failed allocation leaves the buffer as it was
+  EXPECT_FALSE(buffer.grow(SIZE_MAX / 2));
+  EXPECT_EQ(buffer.size(), 64u);
+  EXPECT_EQ(std::memcmp(buffer.data(), "cdef", 4), 0);
+  // Growing to a smaller size changes nothing
+  EXPECT_TRUE(buffer.grow(8));
+  EXPECT_EQ(buffer.size(), 64u);
+}
+
 }  // namespace esphome::online_image::testing

tests/components/runtime_image/test_decoder_reuse.cpp

@@ -4,9 +4,11 @@
 #include <algorithm>
 #include <array>
 #include <cstring>
+#include <utility>
 #include <vector>
 
 #include "esphome/components/runtime_image/image_decoder.h"
+#include "esphome/components/runtime_image/jpeg_decoder.h"
 #include "esphome/components/runtime_image/runtime_image.h"
 
 namespace esphome::runtime_image::testing {
@@ -362,6 +364,23 @@ static std::vector<uint8_t> pixel_bytes(TestableRuntimeImage &img) {
   return std::vector<uint8_t>(start, start + img.get_width_stride() * img.get_height());
 }
 
+// Shrinking a PNG keeps the first source pixel of each span, as the JPEG path does: the even rows and columns
+TEST(RuntimeImageDecoder, ShrunkPngKeepsTheFirstPixelOfEachSpan) {
+  TestableRuntimeImage img(PNG, image::IMAGE_TYPE_RGB, false, 2, 2);
+  ASSERT_TRUE(decode_all(img, PNG_RGB, sizeof(PNG_RGB), PNG));
+  ASSERT_EQ(img.get_width(), 2);
+  ASSERT_EQ(img.get_height(), 2);
+  for (int row = 0; row < 2; row++) {
+    for (int col = 0; col < 2; col++) {
+      const Color pixel = img.get_pixel(col, row);
+      const uint8_t *expected = PNG_RGB_EXPECTED[row * 2][col * 2];
+      EXPECT_EQ(pixel.r, expected[0]) << col << "," << row;
+      EXPECT_EQ(pixel.g, expected[1]) << col << "," << row;
+      EXPECT_EQ(pixel.b, expected[2]) << col << "," << row;
+    }
+  }
+}
+
 TEST(RuntimeImageDecoder, JpegDecoderStaysWarmAcrossDecodes) {
   TestableRuntimeImage img(JPEG);
 
@@ -377,6 +396,12 @@ TEST(RuntimeImageDecoder, JpegDecoderStaysWarmAcrossDecodes) {
   EXPECT_EQ(pixel_bytes(img), first_pixels) << "reused decoder must reproduce identical pixels";
 }
 
+// The RGB565 word at (x, y) of a decoded image, in its own byte order
+static uint16_t rgb565_word(const TestableRuntimeImage &img, int x, int y) {
+  const uint8_t *p = img.get_data_start() + (y * img.get_width() + x) * 2;
+  return p[0] | (p[1] << 8);
+}
+
 // JPEGDEC's colour conversion differs by one step between its SIMD and scalar builds, so each
 // channel is checked within one step; the byte order is still exact
 static void expect_rgb565_near(uint16_t actual, uint16_t expected, const char *order, size_t pixel) {
@@ -386,16 +411,12 @@ static void expect_rgb565_near(uint16_t actual, uint16_t expected, const char *o
 }
 
 TEST(RuntimeImageDecoder, JpegDecodesDirectlyToScaledRgb565WithBothByteOrders) {
-  // Halving the 8x8 gradient keeps its even rows and columns. The words are JPEGDEC's output for those
-  // pixels, red in the top five bits: a decode of the fixture with PIL gives (51, 7, 30) for source
-  // pixel (2, 0), which is word 0x3803 here.
-  static const uint16_t EXPECTED[4 * 4] = {
-      0x0000, 0x3803, 0x8008, 0xB80B, 0x0203, 0x3A07, 0x81EC, 0xBA0F,
-      0x03E7, 0x3C0B, 0x83F0, 0xBC13, 0x05EC, 0x3E0F, 0x85F4, 0xBE17,
-  };
+  // Halving the 8x8 gradient makes JPEGDEC decode it at half size, which averages each 2x2 block of pixels
+  TestableRuntimeImage full(JPEG, image::IMAGE_TYPE_RGB565, false, 8, 8);
   TestableRuntimeImage rgb565_little_endian(JPEG, image::IMAGE_TYPE_RGB565, false, 4, 4);
   TestableRuntimeImage rgb565_big_endian(JPEG, image::IMAGE_TYPE_RGB565, true, 4, 4);
 
+  ASSERT_TRUE(decode_all(full, JPEG_GRADIENT, sizeof(JPEG_GRADIENT)));
   ASSERT_TRUE(decode_all(rgb565_little_endian, JPEG_GRADIENT, sizeof(JPEG_GRADIENT)));
   ASSERT_TRUE(decode_all(rgb565_big_endian, JPEG_GRADIENT, sizeof(JPEG_GRADIENT)));
   ASSERT_EQ(rgb565_little_endian.get_width(), 4);
@@ -405,9 +426,53 @@ TEST(RuntimeImageDecoder, JpegDecodesDirectlyToScaledRgb565WithBothByteOrders) {
 
   const uint8_t *little = rgb565_little_endian.get_data_start();
   const uint8_t *big = rgb565_big_endian.get_data_start();
-  for (size_t i = 0; i < 4 * 4; i++) {
-    expect_rgb565_near(little[i * 2] | (little[i * 2 + 1] << 8), EXPECTED[i], "little-endian", i);
-    expect_rgb565_near((big[i * 2] << 8) | big[i * 2 + 1], EXPECTED[i], "big-endian", i);
+  for (int row = 0; row < 4; row++) {
+    for (int col = 0; col < 4; col++) {
+      int red = 0;
+      int green = 0;
+      int blue = 0;
+      for (int dy = 0; dy < 2; dy++) {
+        for (int dx = 0; dx < 2; dx++) {
+          const uint16_t word = rgb565_word(full, col * 2 + dx, row * 2 + dy);
+          red += word >> 11;
+          green += (word >> 5) & 0x3F;
+          blue += word & 0x1F;
+        }
+      }
+      const uint16_t expected = ((red + 2) / 4) << 11 | ((green + 2) / 4) << 5 | (blue + 2) / 4;
+      const size_t i = row * 4 + col;
+      expect_rgb565_near(little[i * 2] | (little[i * 2 + 1] << 8), expected, "little-endian", i);
+      expect_rgb565_near((big[i * 2] << 8) | big[i * 2 + 1], expected, "big-endian", i);
+    }
+  }
+}
+
+// The generic draw() path gets JPEGDEC's half size RGB8888 output, so it too averages each 2x2 block of pixels
+TEST(RuntimeImageDecoder, JpegDecodesToScaledRgb) {
+  TestableRuntimeImage full(JPEG, image::IMAGE_TYPE_RGB, false, 8, 8);
+  TestableRuntimeImage half(JPEG, image::IMAGE_TYPE_RGB, false, 4, 4);
+  ASSERT_TRUE(decode_all(full, JPEG_GRADIENT, sizeof(JPEG_GRADIENT)));
+  ASSERT_TRUE(decode_all(half, JPEG_GRADIENT, sizeof(JPEG_GRADIENT)));
+  ASSERT_EQ(static_cast<JpegDecoder *>(half.decoder())->get_scale(), 2);
+
+  for (int row = 0; row < 4; row++) {
+    for (int col = 0; col < 4; col++) {
+      int red = 0;
+      int green = 0;
+      int blue = 0;
+      for (int dy = 0; dy < 2; dy++) {
+        for (int dx = 0; dx < 2; dx++) {
+          const Color pixel = full.get_pixel(col * 2 + dx, row * 2 + dy);
+          red += pixel.r;
+          green += pixel.g;
+          blue += pixel.b;
+        }
+      }
+      const Color pixel = half.get_pixel(col, row);
+      EXPECT_NEAR(pixel.r, (red + 2) / 4, 8) << "pixel " << col << "," << row << " red";
+      EXPECT_NEAR(pixel.g, (green + 2) / 4, 8) << "pixel " << col << "," << row << " green";
+      EXPECT_NEAR(pixel.b, (blue + 2) / 4, 8) << "pixel " << col << "," << row << " blue";
+    }
   }
 }
 
@@ -415,10 +480,15 @@ TEST(RuntimeImageDecoder, JpegDecodesDirectlyToScaledRgb565WithBothByteOrders) {
 // prepare_rgb565_scaling_ rounds: source n covers targets ceil(n * target / source) up to the next start
 static uint16_t scaled_boundary(int n, int source, int target) { return (n * target + source - 1) / source; }
 
-// The RGB565 word at (x, y) of a decoded image, in its own byte order
-static uint16_t rgb565_word(const TestableRuntimeImage &img, int x, int y) {
-  const uint8_t *p = img.get_data_start() + (y * img.get_width() + x) * 2;
-  return p[0] | (p[1] << 8);
+// JPEGDEC decodes at the smallest of full, 1/2, 1/4 and 1/8 size that still covers the buffer
+TEST(RuntimeImageDecoder, JpegDecodesAtTheSmallestSizeThatCoversTheBuffer) {
+  for (auto [size, scale] :
+       {std::pair{8, 1}, std::pair{5, 1}, std::pair{4, 2}, std::pair{3, 2}, std::pair{2, 4}, std::pair{1, 8}}) {
+    TestableRuntimeImage img(JPEG, image::IMAGE_TYPE_RGB565, false, size, size);
+    ASSERT_TRUE(decode_all(img, JPEG_GRADIENT, sizeof(JPEG_GRADIENT)));
+    EXPECT_EQ(img.get_width(), size);
+    EXPECT_EQ(static_cast<JpegDecoder *>(img.decoder())->get_scale(), scale) << size << "x" << size;
+  }
 }
 
 // Every scaled direct decode must equal the unscaled one sampled through the boundary table,
@@ -427,7 +497,8 @@ TEST(RuntimeImageDecoder, JpegDirectRgb565ScalesBySourcePixelSpans) {
   TestableRuntimeImage full(JPEG, image::IMAGE_TYPE_RGB565, false, 8, 8);
   ASSERT_TRUE(decode_all(full, JPEG_GRADIENT, sizeof(JPEG_GRADIENT)));
 
-  for (int size : {4, 6, 16}) {
+  // Sizes JPEGDEC cannot reach by scaling, so the full size decode is spread over the buffer
+  for (int size : {5, 6, 16}) {
     TestableRuntimeImage scaled(JPEG, image::IMAGE_TYPE_RGB565, false, size, size);
     ASSERT_TRUE(decode_all(scaled, JPEG_GRADIENT, sizeof(JPEG_GRADIENT)));
     ASSERT_EQ(scaled.get_width(), size);

tests/components/runtime_image/test_grayscale_pixel.cpp

@@ -0,0 +1,35 @@
+#include <gtest/gtest.h>
+
+#include <cstdint>
+#include <cstdlib>
+
+#include "esphome/components/runtime_image/runtime_image.h"
+
+namespace esphome::runtime_image::testing {
+
+class GrayscaleImage : public RuntimeImage {
+ public:
+  GrayscaleImage() : RuntimeImage(BMP, image::IMAGE_TYPE_GRAYSCALE, image::TRANSPARENCY_OPAQUE) {}
+  uint8_t pixel(int x) const { return this->buffer_[x]; }
+};
+
+// The integer weights stay within one step of the floating point formula they replace, and keep white at 255
+TEST(GrayscalePixel, MatchesTheFloatingPointWeights) {
+  GrayscaleImage img;
+  ASSERT_GT(img.resize(256, 1), 0);
+  for (int r = 0; r < 256; r += 5) {
+    for (int g = 0; g < 256; g += 5) {
+      for (int b = 0; b < 256; b += 5) {
+        img.draw_pixel(0, 0, Color(r, g, b));
+        const int expected = static_cast<int>(0.2125 * r + 0.7154 * g + 0.0721 * b);
+        ASSERT_LE(std::abs(img.pixel(0) - expected), 1) << "r=" << r << " g=" << g << " b=" << b;
+      }
+    }
+  }
+  img.draw_pixel(1, 0, Color(255, 255, 255));
+  EXPECT_EQ(img.pixel(1), 255);
+  img.draw_pixel(2, 0, Color(0, 0, 0));
+  EXPECT_EQ(img.pixel(2), 0);
+}
+
+}  // namespace esphome::runtime_image::testing

tests/components/runtime_image/test_jpeg_source.cpp

@@ -5,6 +5,7 @@
 #include <vector>
 
 #include "esphome/components/runtime_image/image_decoder.h"
+#include "esphome/components/runtime_image/jpeg_decoder.h"
 #include "esphome/components/runtime_image/runtime_image.h"
 
 #ifdef USE_RUNTIME_IMAGE_JPEG
@@ -178,6 +179,7 @@ class SourceImage : public RuntimeImage {
   explicit SourceImage(image::ImageType type = image::IMAGE_TYPE_RGB, int width = 0, int height = 0)
       : RuntimeImage(JPEG, type, image::TRANSPARENCY_OPAQUE, nullptr, false, width, height) {}
   size_t decoded_bytes() const { return this->decoded_bytes_; }
+  int scale() const { return static_cast<const JpegDecoder *>(this->decoder_.get())->get_scale(); }
 };
 
 /// The file in memory; fails reads once fail_at bytes have been read
@@ -291,6 +293,23 @@ TEST(JpegSourceDecode, SteppedDirectRgb565MatchesFedDecode) {
   EXPECT_EQ(pixels(stepped), pixels(fed));
 }
 
+// decodeBegin() is given the same reduced scale as decode(), and decodeRows() keeps it for every step
+TEST(JpegSourceDecode, SteppedScaledDecodeMatchesFedDecode) {
+  for (auto type : {image::IMAGE_TYPE_RGB565, image::IMAGE_TYPE_RGB}) {
+    // 24x20 is half of 48x40, so JPEGDEC decodes at 1/2 size
+    SourceImage fed(type, 24, 20);
+    ASSERT_TRUE(decode_fed(fed));
+    ASSERT_EQ(fed.scale(), 2);
+
+    SourceImage stepped(type, 24, 20);
+    MemorySource source(JPEG_ROWS, sizeof(JPEG_ROWS));
+    int steps;
+    ASSERT_EQ(decode_stepped(stepped, source, steps), DECODE_STEP_DONE);
+    ASSERT_EQ(stepped.scale(), 2);
+    EXPECT_EQ(pixels(stepped), pixels(fed)) << "image type " << type;
+  }
+}
+
 TEST(JpegSourceDecode, WaitsForDataThatHasNotArrived) {
   SourceImage fed;
   ASSERT_TRUE(decode_fed(fed));