Fixed GL_RenderReadPixels() - thanks Ryan!

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%404188

src/video/SDL_renderer_gl.c

@@ -1257,6 +1257,7 @@ GL_RenderReadPixels(SDL_Renderer * renderer, const SDL_Rect * rect,
                     Uint32 pixel_format, void * pixels, int pitch)
 {
     GL_RenderData *data = (GL_RenderData *) renderer->driverdata;
+    SDL_Window *window = SDL_GetWindowFromID(renderer->window);
     GLint internalFormat;
     GLenum format, type;
     Uint8 *src, *dst, *tmp;
@@ -1276,13 +1277,10 @@ GL_RenderReadPixels(SDL_Renderer * renderer, const SDL_Rect * rect,
     data->glPixelStorei(GL_PACK_ALIGNMENT, 1);
     data->glPixelStorei(GL_PACK_ROW_LENGTH,
                         (pitch / bytes_per_pixel(pixel_format)));
-    data->glReadBuffer(GL_FRONT);
 
-memset(pixels, 0xff, rect->h*pitch);
-    data->glReadPixels(rect->x, rect->y+rect->h-1, rect->w, rect->h,
+    data->glReadPixels(rect->x, (window->h-rect->y)-rect->h, rect->w, rect->h,
                        format, type, pixels);
 
-#if 0
     /* Flip the rows to be top-down */
     length = rect->w * bytes_per_pixel(pixel_format);
     src = (Uint8*)pixels + (rect->h-1)*pitch;
@@ -1293,9 +1291,10 @@ memset(pixels, 0xff, rect->h*pitch);
         SDL_memcpy(tmp, dst, length);
         SDL_memcpy(dst, src, length);
         SDL_memcpy(src, tmp, length);
+        dst += pitch;
+        src -= pitch;
     }
     SDL_stack_free(tmp);
-#endif
 
     return 0;
 }