[runtime_image] Add CodSpeed benchmarks for JPEG decoding (#20603)

tests/benchmarks/components/runtime_image/bench_jpeg_decode.cpp

@@ -0,0 +1,64 @@
+#include <benchmark/benchmark.h>
+
+#include <vector>
+
+#include "esphome/components/runtime_image/runtime_image.h"
+#include "jpeg_96x96.h"
+
+namespace esphome::benchmarks {
+
+using runtime_image::RuntimeImage;
+
+// A fixed-size image so every decode scales the same JPEG into the same buffer
+class BenchImage : public RuntimeImage {
+ public:
+  BenchImage(image::ImageType type, int width, int height)
+      : RuntimeImage(runtime_image::JPEG, type, image::TRANSPARENCY_OPAQUE, nullptr, false, width, height) {}
+};
+
+// One full decode session, fed the way online_image feeds a download
+static bool decode(BenchImage &img, std::vector<uint8_t> &buffer) {
+  if (!img.begin_decode(buffer.size(), runtime_image::JPEG)) {
+    return false;
+  }
+  size_t offset = 0;
+  while (offset < buffer.size()) {
+    const int consumed = img.feed_data(buffer.data() + offset, buffer.size() - offset);
+    if (consumed <= 0) {
+      return false;
+    }
+    offset += consumed;
+  }
+  return img.end_decode();
+}
+
+static void run(benchmark::State &state, image::ImageType type, int width, int height) {
+  BenchImage img(type, width, height);
+  std::vector<uint8_t> buffer(JPEG_96X96, JPEG_96X96 + JPEG_96X96_SIZE);
+  for (auto _ : state) {
+    if (!decode(img, buffer)) {
+      state.SkipWithError("decode failed");
+      return;
+    }
+    benchmark::DoNotOptimize(img.get_data_start());
+  }
+  state.SetItemsProcessed(state.iterations() * static_cast<int64_t>(width) * height);
+}
+
+// --- JPEG into an RGB565 image: same size, half size and double size ---
+
+static void JpegDecode_Rgb565_Native(benchmark::State &state) { run(state, image::IMAGE_TYPE_RGB565, 96, 96); }
+BENCHMARK(JpegDecode_Rgb565_Native);
+
+static void JpegDecode_Rgb565_Half(benchmark::State &state) { run(state, image::IMAGE_TYPE_RGB565, 48, 48); }
+BENCHMARK(JpegDecode_Rgb565_Half);
+
+static void JpegDecode_Rgb565_Double(benchmark::State &state) { run(state, image::IMAGE_TYPE_RGB565, 192, 192); }
+BENCHMARK(JpegDecode_Rgb565_Double);
+
+// --- JPEG into an RGB image at the same size, the generic per-pixel path for reference ---
+
+static void JpegDecode_Rgb_Native(benchmark::State &state) { run(state, image::IMAGE_TYPE_RGB, 96, 96); }
+BENCHMARK(JpegDecode_Rgb_Native);
+
+}  // namespace esphome::benchmarks