Commit b528d48446c8c9c005ad122dddfdb2b46ad4553a
2021-10-22T16:59:46
wayland: Wayland cursors should use premultiplied alpha It turns out that Wayland's WL_SHM_FORMAT_ARGB8888 format (and, indeed, all wayland RGBA formats) should be treated as premultiplied. SDL surfaces tend not to be premultiplied, and this is assumed by other backends when dealing with cursors. This change premultiplies the cursor surface in Wayland_CreateCursor() using the new SDL_PremultiplySurfaceAlphaToARGB8888(). In so doing, it also adds support for a wider range of input surfaces, including those with non-ARGB8888 pixel formats, and those which don't have pitch==width. This should fix #4856
diff --git a/src/video/wayland/SDL_waylandmouse.c b/src/video/wayland/SDL_waylandmouse.c
index 5de1d45..19a439f 100644
--- a/src/video/wayland/SDL_waylandmouse.c
+++ b/src/video/wayland/SDL_waylandmouse.c
@@ -34,6 +34,7 @@
#include "SDL_mouse.h"
#include "../../events/SDL_mouse_c.h"
#include "SDL_waylandvideo.h"
+#include "../SDL_pixels_c.h"
#include "SDL_waylandevents_c.h"
#include "wayland-cursor.h"
@@ -267,10 +268,6 @@ Wayland_CreateCursor(SDL_Surface *surface, int hot_x, int hot_y)
}
cursor->driverdata = (void *) data;
- /* Assume ARGB8888 */
- SDL_assert(surface->format->format == SDL_PIXELFORMAT_ARGB8888);
- SDL_assert(surface->pitch == surface->w * 4);
-
/* Allocate shared memory buffer for this cursor */
if (create_buffer_from_shm (data,
surface->w,
@@ -282,9 +279,8 @@ Wayland_CreateCursor(SDL_Surface *surface, int hot_x, int hot_y)
return NULL;
}
- SDL_memcpy(data->shm_data,
- surface->pixels,
- surface->h * surface->pitch);
+ /* Wayland requires premultiplied alpha for its surfaces. */
+ SDL_PremultiplySurfaceAlphaToARGB8888(surface, data->shm_data);
data->surface = wl_compositor_create_surface(wd->compositor);
wl_surface_set_user_data(data->surface, NULL);