Fix failing tests on non-libpng backends

src_c/imageext.c

@@ -148,6 +148,25 @@ image_load_ext(PyObject *self, PyObject *arg, PyObject *kwarg)
         return RAISE(pgExc_SDLError, IMG_GetError());
     }
 
+    /* Vendor in fix from https://github.com/libsdl-org/SDL_image/pull/559.
+     * When that PR is merged this block can be removed. */
+    if (SDL_ISPIXELFORMAT_INDEXED(PG_SURF_FORMATENUM(surf))) {
+        Uint32 colorkey;
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+        if (SDL_GetSurfaceColorKey(surf, &colorkey))
+#else
+        if (SDL_GetColorKey(surf, &colorkey) == 0)
+#endif
+        {
+            SDL_Palette *pal = PG_GetSurfacePalette(surf);
+            if (pal && colorkey < (Uint32)pal->ncolors) {
+                SDL_Color c = pal->colors[colorkey];
+                c.a = SDL_ALPHA_OPAQUE;
+                SDL_SetPaletteColors(pal, &c, (int)colorkey, 1);
+            }
+        }
+    }
+
     final = (PyObject *)pgSurface_New(surf);
     if (final == NULL) {
         SDL_FreeSurface(surf);

test/image_test.py

@@ -20,6 +20,8 @@
         _sdl_image_ver <= (2, 0, 5) and pygame.get_sdl_byteorder() == pygame.BIG_ENDIAN
     )
 
+PG_DEPS_FROM_SYSTEM = "PG_DEPS_FROM_SYSTEM" in os.environ
+
 
 def check_magic(f, magic_hexes):
     """Tests a given file to see if the magic hex matches."""
@@ -203,6 +205,11 @@ def testSavePNG32(self):
         pygame.image.get_sdl_image_version() == (2, 0, 5),
         "SDL image 2.0.5 png saving will save this 24 bit as RGBA, causing reader.asRGB8 to fail",
     )
+    @unittest.skipIf(
+        PG_DEPS_FROM_SYSTEM,
+        "If we are using system dependencies, we don't know the backend used "
+        "for PNG saving, and this test only works with libpng.",
+    )
     def testSavePNG24(self):
         """see if we can save a png with color values in the proper channels."""
         # Create a PNG file with known colors
@@ -238,6 +245,11 @@ def testSavePNG24(self):
             del reader
             os.remove(f_path)
 
+    @unittest.skipIf(
+        PG_DEPS_FROM_SYSTEM,
+        "If we are using system dependencies, we don't know the backend used "
+        "for PNG saving, and this test only works with libpng.",
+    )
     def testSavePNG8(self):
         """see if we can save an 8 bit png correctly"""
         # Create an 8-bit PNG file with known colors
@@ -269,7 +281,7 @@ def testSavePNG8(self):
             os.remove(f_path)
 
     @unittest.skipIf(
-        "PG_DEPS_FROM_SYSTEM" in os.environ,
+        PG_DEPS_FROM_SYSTEM,
         "If we are using system dependencies, we don't know the backend used "
         "for PNG saving, and this test only works with libpng.",
     )

test/surface_test.py

@@ -1228,8 +1228,12 @@ def test_image_convert_bug_131(self):
             im = pygame.image.load(example_path(os.path.join("data", "city.png")))
             im2 = pygame.image.load(example_path(os.path.join("data", "brick.png")))
 
-            self.assertEqual(im.get_palette(), ((0, 0, 0, 255), (255, 255, 255, 255)))
-            self.assertEqual(im2.get_palette(), ((0, 0, 0, 255), (0, 0, 0, 255)))
+            # Only validate the first two entries; stbimage backend gives a 256
+            # length palette while libpng doesn't.
+            self.assertEqual(
+                im.get_palette()[:2], ((0, 0, 0, 255), (255, 255, 255, 255))
+            )
+            self.assertEqual(im2.get_palette()[:2], ((0, 0, 0, 255), (0, 0, 0, 255)))
 
             self.assertEqual(
                 repr(im.convert(32)), "<Surface(24x24x32, colorkey=(0, 0, 0, 255))>"