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shape: Use SDL[Test]_ReadSurfacePixel 

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>
main
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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44
src/video/SDL_shape.c
View File

@ -22,6 +22,7 @@
#include "SDL_sysvideo.h" #include "SDL_sysvideo.h"
#include "SDL_shape_internals.h" #include "SDL_shape_internals.h"
#include "SDL_video_c.h"
SDL_Window *SDL_CreateShapedWindow(const char *title, int w, int h, Uint32 flags) SDL_Window *SDL_CreateShapedWindow(const char *title, int w, int h, Uint32 flags)
{ {
@ -60,8 +61,7 @@ void SDL_CalculateShapeBitmap(SDL_WindowShapeMode mode, SDL_Surface *shape, Uint
int x = 0; int x = 0;
int y = 0; int y = 0;
Uint8 r = 0, g = 0, b = 0, alpha = 0; Uint8 r = 0, g = 0, b = 0, alpha = 0;
Uint8 *pixel = NULL; Uint32 mask_value = 0;
Uint32 pixel_value = 0, mask_value = 0;
size_t bytes_per_scanline = (size_t)(shape->w + (ppb - 1)) / ppb; size_t bytes_per_scanline = (size_t)(shape->w + (ppb - 1)) / ppb;
Uint8 *bitmap_scanline; Uint8 *bitmap_scanline;
SDL_Color key; SDL_Color key;
@ -75,24 +75,10 @@ void SDL_CalculateShapeBitmap(SDL_WindowShapeMode mode, SDL_Surface *shape, Uint
for (y = 0; y < shape->h; y++) { for (y = 0; y < shape->h; y++) {
bitmap_scanline = bitmap + y * bytes_per_scanline; bitmap_scanline = bitmap + y * bytes_per_scanline;
for (x = 0; x < shape->w; x++) { for (x = 0; x < shape->w; x++) {
alpha = 0; if (SDL_ReadSurfacePixel(shape, x, y, &r, &g, &b, &alpha) != 0) {
pixel_value = 0; continue;
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;
} }
SDL_GetRGBA(pixel_value, shape->format, &r, &g, &b, &alpha);
switch (mode.mode) { switch (mode.mode) {
case (ShapeModeDefault): case (ShapeModeDefault):
mask_value = (alpha >= 1 ? 1 : 0); mask_value = (alpha >= 1 ? 1 : 0);
@ -120,8 +106,6 @@ void SDL_CalculateShapeBitmap(SDL_WindowShapeMode mode, SDL_Surface *shape, Uint
static SDL_ShapeTree *RecursivelyCalculateShapeTree(SDL_WindowShapeMode mode, SDL_Surface *mask, SDL_Rect dimensions) static SDL_ShapeTree *RecursivelyCalculateShapeTree(SDL_WindowShapeMode mode, SDL_Surface *mask, SDL_Rect dimensions)
{ {
int x = 0, y = 0; int x = 0, y = 0;
Uint8 *pixel = NULL;
Uint32 pixel_value = 0;
Uint8 r = 0, g = 0, b = 0, a = 0; Uint8 r = 0, g = 0, b = 0, a = 0;
SDL_bool pixel_opaque = SDL_FALSE; SDL_bool pixel_opaque = SDL_FALSE;
int last_opaque = -1; int last_opaque = -1;
@ -136,23 +120,9 @@ static SDL_ShapeTree *RecursivelyCalculateShapeTree(SDL_WindowShapeMode mode, SD
for (y = dimensions.y; y < dimensions.y + dimensions.h; y++) { for (y = dimensions.y; y < dimensions.y + dimensions.h; y++) {
for (x = dimensions.x; x < dimensions.x + dimensions.w; x++) { for (x = dimensions.x; x < dimensions.x + dimensions.w; x++) {
pixel_value = 0; if (SDL_ReadSurfacePixel(mask, x, y, &r, &g, &b, &a) != 0) {
pixel = (Uint8 *)(mask->pixels) + (y * mask->pitch) + (x * mask->format->BytesPerPixel); continue;
switch (mask->format->BytesPerPixel) {
case (1):
pixel_value = *pixel;
break;
case (2):
pixel_value = *(Uint16 *)pixel;
break;
case (3):
pixel_value = *(Uint32 *)pixel & (~mask->format->Amask);
break;
case (4):
pixel_value = *(Uint32 *)pixel;
break;
} }
SDL_GetRGBA(pixel_value, mask->format, &r, &g, &b, &a);
switch (mode.mode) { switch (mode.mode) {
case (ShapeModeDefault): case (ShapeModeDefault):
pixel_opaque = (a >= 1 ? SDL_TRUE : SDL_FALSE); pixel_opaque = (a >= 1 ? SDL_TRUE : SDL_FALSE);

22
test/testshape.c
View File

@ -42,8 +42,7 @@ static void SDL_CalculateShapeBitmap(SDL_WindowShapeMode mode, SDL_Surface *shap
int x = 0; int x = 0;
int y = 0; int y = 0;
Uint8 r = 0, g = 0, b = 0, alpha = 0; Uint8 r = 0, g = 0, b = 0, alpha = 0;
Uint8 *pixel = NULL; Uint32 mask_value = 0;
Uint32 pixel_value = 0, mask_value = 0;
size_t bytes_per_scanline = (size_t)(shape->w + (ppb - 1)) / ppb; size_t bytes_per_scanline = (size_t)(shape->w + (ppb - 1)) / ppb;
Uint8 *bitmap_scanline; Uint8 *bitmap_scanline;
SDL_Color key; SDL_Color key;
@ -58,23 +57,10 @@ static void SDL_CalculateShapeBitmap(SDL_WindowShapeMode mode, SDL_Surface *shap
bitmap_scanline = bitmap + y * bytes_per_scanline; bitmap_scanline = bitmap + y * bytes_per_scanline;
for (x = 0; x < shape->w; x++) { for (x = 0; x < shape->w; x++) {
alpha = 0; alpha = 0;
pixel_value = 0; if (SDLTest_ReadSurfacePixel(shape, x, y, &r, &g, &b, &alpha) != 0) {
pixel = (Uint8 *)(shape->pixels) + (y * shape->pitch) + (x * shape->format->BytesPerPixel); continue;
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;
} }
SDL_GetRGBA(pixel_value, shape->format, &r, &g, &b, &alpha);
switch (mode.mode) { switch (mode.mode) {
case (ShapeModeDefault): case (ShapeModeDefault):
mask_value = (alpha >= 1 ? 1 : 0); mask_value = (alpha >= 1 ? 1 : 0);