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Proper transparency color recognition

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This commit is contained in:
jpirnay
2026-03-02 11:22:55 +01:00
parent 0c673f4e92
commit b8109a2c5e
1 changed files with 20 additions and 1 deletions
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src/activities/boot_sleep/SleepActivity.cpp
+20 -1
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@@ -20,7 +20,6 @@
#include "images/Logo120.h"
#include "util/StringUtils.h"
namespace {
// Context passed through PNGdec's decode() user-pointer to the per-scanline draw callback.
@@ -34,6 +33,9 @@ struct PngOverlayCtx {
int dstY;
float yScale;
int lastDstY;
// Color-key transparency (tRNS chunk) for TRUECOLOR and GRAYSCALE images.
// -1 means no color key. For TRUECOLOR: 0x00RRGGBB; for GRAYSCALE: low byte only.
int32_t transparentColor;
};
// PNGdec file I/O callbacks — mirror the pattern in PngToFramebufferConverter.cpp.
@@ -99,10 +101,20 @@ int pngOverlayDraw(PNGDRAW* pDraw) {
case PNG_PIXEL_TRUECOLOR: {
const uint8_t* p = &pixels[srcX * 3];
gray = (uint8_t)((p[0] * 77 + p[1] * 150 + p[2] * 29) >> 8);
// tRNS color-key: if pixel matches the designated transparent color, skip it
if (ctx->transparentColor >= 0 && p[0] == (uint8_t)((ctx->transparentColor >> 16) & 0xFF) &&
p[1] == (uint8_t)((ctx->transparentColor >> 8) & 0xFF) &&
p[2] == (uint8_t)(ctx->transparentColor & 0xFF)) {
alpha = 0;
}
break;
}
case PNG_PIXEL_GRAYSCALE:
gray = pixels[srcX];
// tRNS color-key: transparent gray value stored in low byte
if (ctx->transparentColor >= 0 && gray == (uint8_t)(ctx->transparentColor & 0xFF)) {
alpha = 0;
}
break;
case PNG_PIXEL_INDEXED:
if (pDraw->pPalette) {
@@ -508,6 +520,13 @@ void SleepActivity::renderOverlaySleepScreen() const {
ctx.dstY = (pageHeight - dstH) / 2;
ctx.yScale = yScale;
ctx.lastDstY = -1;
// Populate color-key transparency for TRUECOLOR/GRAYSCALE PNGs with a tRNS chunk.
// TRUECOLOR_ALPHA and GRAY_ALPHA carry per-pixel alpha, handled directly in the callback.
// INDEXED+tRNS stores per-palette alpha at pPalette[768+idx], also handled there.
const int pixType = png->getPixelType();
ctx.transparentColor = (png->hasAlpha() && (pixType == PNG_PIXEL_TRUECOLOR || pixType == PNG_PIXEL_GRAYSCALE))
? (int32_t)png->getTransparentColor()
: -1;
rc = png->decode(&ctx, 0);
png->close();