From 04edb38cdf856c367ba1c167f6d485c21bbcfdb1 Mon Sep 17 00:00:00 2001
From: Simon McVittie <[EMAIL REDACTED]>
Date: Mon, 2 Oct 2023 19:50:47 +0100
Subject: [PATCH] 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>
---
src/video/SDL_shape.c | 44 +++++++------------------------------------
test/testshape.c | 22 ++++------------------
2 files changed, 11 insertions(+), 55 deletions(-)
diff --git a/src/video/SDL_shape.c b/src/video/SDL_shape.c
index 3082c1bdcfb9..cbbfa7e61621 100644
--- a/src/video/SDL_shape.c
+++ b/src/video/SDL_shape.c
@@ -22,6 +22,7 @@
#include "SDL_sysvideo.h"
#include "SDL_shape_internals.h"
+#include "SDL_video_c.h"
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 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;
@@ -75,24 +75,10 @@ void SDL_CalculateShapeBitmap(SDL_WindowShapeMode mode, SDL_Surface *shape, Uint
for (y = 0; y < shape->h; y++) {
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 (SDL_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);
@@ -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)
{
int x = 0, y = 0;
- Uint8 *pixel = NULL;
- Uint32 pixel_value = 0;
Uint8 r = 0, g = 0, b = 0, a = 0;
SDL_bool pixel_opaque = SDL_FALSE;
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 (x = dimensions.x; x < dimensions.x + dimensions.w; x++) {
- pixel_value = 0;
- pixel = (Uint8 *)(mask->pixels) + (y * mask->pitch) + (x * mask->format->BytesPerPixel);
- 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;
+ if (SDL_ReadSurfacePixel(mask, x, y, &r, &g, &b, &a) != 0) {
+ continue;
}
- SDL_GetRGBA(pixel_value, mask->format, &r, &g, &b, &a);
switch (mode.mode) {
case (ShapeModeDefault):
pixel_opaque = (a >= 1 ? SDL_TRUE : SDL_FALSE);
diff --git a/test/testshape.c b/test/testshape.c
index 078319794a99..6965b3aca73e 100644
--- a/test/testshape.c
+++ b/test/testshape.c
@@ -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);