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[display] Share the packed pixel read through ColorUtil

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ColorUtil::read_packed<BITNESS>() lives next to to_color() so drivers
with their own blit loop (it8951 carries a copy of the same switch)
can pick it up; the comments say where the folding happens.
This commit is contained in:
J. Nick Koston
2026-09-17 18:01:44 -05:00
parent 2b894cd255
commit a35fcc12c3
2 changed files with 26 additions and 24 deletions
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esphome/components/display/display.cpp
+4 -24
View File
@@ -53,27 +53,6 @@ void Display::line_at_angle(int x, int y, int angle, int start_radius, int stop_
this->line(x1, y1, x2, y2, color);
}
// Reads one source pixel of draw_pixels_at(). BITNESS is a template argument so
// the byte layout folds and to_color()'s channel scaling divides by a constant,
// which the compiler turns into a multiply and shift; at runtime it was three
// divisions per pixel.
template<ColorBitness BITNESS>
static inline ESPHOME_ALWAYS_INLINE uint32_t read_packed_pixel(const uint8_t *ptr, size_t source_idx, bool big_endian) {
if constexpr (BITNESS == COLOR_BITNESS_565) {
const size_t idx = source_idx * 2;
if (big_endian)
return (ptr[idx] << 8) + ptr[idx + 1];
return ptr[idx] + (ptr[idx + 1] << 8);
} else if constexpr (BITNESS == COLOR_BITNESS_888) {
const size_t idx = source_idx * 3;
if (big_endian)
return (ptr[idx + 0] << 16) + (ptr[idx + 1] << 8) + ptr[idx + 2];
return ptr[idx + 0] + (ptr[idx + 1] << 8) + (ptr[idx + 2] << 16);
} else {
return ptr[source_idx];
}
}
// flatten keeps to_color() inlined in the pixel loop; in PSRAM builds GCC at
// -Os stops inlining it once there are two call sites, which costs a call and
// spills per pixel. Without PSRAM there is one call site and it changes
@@ -83,10 +62,12 @@ static void __attribute__((flatten))
draw_packed_pixels(Display *display, int x_start, int y_start, int w, int h, const uint8_t *ptr, ColorOrder order,
bool big_endian, int x_offset, int y_offset, int x_pad) {
const size_t line_stride = x_offset + w + x_pad; // length of each source line in pixels
// BITNESS is a constant here, so to_color()'s three per pixel divisions
// become a multiply and shift and its bitness switch folds.
const auto draw_source_pixel = [&](int x, int y, size_t source_idx) ESPHOME_ALWAYS_INLINE {
display->draw_pixel_at(
x + x_start, y + y_start,
ColorUtil::to_color(read_packed_pixel<BITNESS>(ptr, source_idx, big_endian), order, BITNESS));
ColorUtil::to_color(ColorUtil::read_packed<BITNESS>(ptr, source_idx, big_endian), order, BITNESS));
};
// The source and frame buffers are row-major, so walking rows keeps the read
// and the write sequential. When the display swaps the axes before writing,
@@ -104,8 +85,7 @@ draw_packed_pixels(Display *display, int x_start, int y_start, int w, int h, con
return;
}
#endif
// Without PSRAM the frame buffer is in uncached RAM, where the strided write
// is free, so one copy of the loop is enough.
// Row walk: builds without PSRAM, and PSRAM builds whose axes are not swapped.
for (int y = 0; y != h; y++) {
size_t source_idx = (y_offset + y) * line_stride + x_offset;
for (int x = 0; x != w; x++, source_idx++) {
esphome/components/display/display_color_utils.h
+22
View File
@@ -1,5 +1,6 @@
#pragma once
#include "esphome/core/color.h"
#include "esphome/core/helpers.h"
namespace esphome::display {
enum ColorOrder : uint8_t { COLOR_ORDER_RGB = 0, COLOR_ORDER_BGR = 1, COLOR_ORDER_GRB = 2 };
@@ -8,6 +9,27 @@ inline static uint8_t esp_scale(uint8_t i, uint8_t scale, uint8_t max_value = 25
class ColorUtil {
public:
/// Reads one packed pixel of the given bitness from a source buffer into the
/// value to_color() takes. BITNESS is a template argument so the byte layout
/// folds; pass it on to to_color() as a constant too, and its channel scaling
/// divides by a constant, which the compiler turns into a multiply and shift.
template<ColorBitness BITNESS>
static ESPHOME_ALWAYS_INLINE uint32_t read_packed(const uint8_t *ptr, size_t index, bool big_endian) {
if constexpr (BITNESS == COLOR_BITNESS_565) {
const size_t idx = index * 2;
if (big_endian)
return (ptr[idx] << 8) + ptr[idx + 1];
return ptr[idx] + (ptr[idx + 1] << 8);
} else if constexpr (BITNESS == COLOR_BITNESS_888) {
const size_t idx = index * 3;
if (big_endian)
return (ptr[idx + 0] << 16) + (ptr[idx + 1] << 8) + ptr[idx + 2];
return ptr[idx + 0] + (ptr[idx + 1] << 8) + (ptr[idx + 2] << 16);
} else {
return ptr[index];
}
}
static Color to_color(uint32_t colorcode, ColorOrder color_order,
ColorBitness color_bitness = ColorBitness::COLOR_BITNESS_888, bool right_bit_aligned = true) {
uint8_t first_color, second_color, third_color;