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shape: Use SDL[Test]_ReadSurfacePixel

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This avoids assuming that the pixels are suitably aligned for direct
access, which there's no guarantee that they are; in particular,
3-bytes-per-pixel RGB images are likely to have 3 out of 4 pixels
misaligned. On x86, dereferencing a misaligned pointer does what you
would expect, but on other architectures it's undefined whether it will
work, crash with SIGBUS, or silently give a wrong answer.

Signed-off-by: Simon McVittie <smcv@collabora.com>
This commit is contained in:
Simon McVittie
2023-10-02 19:50:47 +01:00
committed by Sam Lantinga
parent f5745c3a67
commit 04edb38cdf
2 changed files with 11 additions and 55 deletions
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22
test/testshape.c
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@@ -42,8 +42,7 @@ static void SDL_CalculateShapeBitmap(SDL_WindowShapeMode mode, SDL_Surface *shap
int x = 0;
int y = 0;
Uint8 r = 0, g = 0, b = 0, alpha = 0;
Uint8 *pixel = NULL;
Uint32 pixel_value = 0, mask_value = 0;
Uint32 mask_value = 0;
size_t bytes_per_scanline = (size_t)(shape->w + (ppb - 1)) / ppb;
Uint8 *bitmap_scanline;
SDL_Color key;
@@ -58,23 +57,10 @@ static void SDL_CalculateShapeBitmap(SDL_WindowShapeMode mode, SDL_Surface *shap
bitmap_scanline = bitmap + y * bytes_per_scanline;
for (x = 0; x < shape->w; x++) {
alpha = 0;
pixel_value = 0;
pixel = (Uint8 *)(shape->pixels) + (y * shape->pitch) + (x * shape->format->BytesPerPixel);
switch (shape->format->BytesPerPixel) {
case (1):
pixel_value = *pixel;
break;
case (2):
pixel_value = *(Uint16 *)pixel;
break;
case (3):
pixel_value = *(Uint32 *)pixel & (~shape->format->Amask);
break;
case (4):
pixel_value = *(Uint32 *)pixel;
break;
if (SDLTest_ReadSurfacePixel(shape, x, y, &r, &g, &b, &alpha) != 0) {
continue;
}
SDL_GetRGBA(pixel_value, shape->format, &r, &g, &b, &alpha);
switch (mode.mode) {
case (ShapeModeDefault):
mask_value = (alpha >= 1 ? 1 : 0);