+int zoomSurfaceRGBA_scaleDownBy2(SDL_Surface *src, SDL_Surface *dst)
+{
+ int x, y;
+ tColorRGBA *sp, *csp, *dp;
+ int sgap, dgap;
+
+ /* pointer setup */
+ sp = csp = (tColorRGBA *) src->pixels;
+ dp = (tColorRGBA *) dst->pixels;
+ sgap = src->pitch - src->w * 4;
+ dgap = dst->pitch - dst->w * 4;
+
+ for (y = 0; y < dst->h; y++)
+ {
+ sp = csp;
+
+ for (x = 0; x < dst->w; x++)
+ {
+ tColorRGBA *sp0 = sp;
+ tColorRGBA *sp1 = (tColorRGBA *) ((Uint8 *) sp + src->pitch);
+ tColorRGBA *sp00 = &sp0[0];
+ tColorRGBA *sp01 = &sp0[1];
+ tColorRGBA *sp10 = &sp1[0];
+ tColorRGBA *sp11 = &sp1[1];
+ tColorRGBA new;
+
+ /* create new color pixel from all four source color pixels */
+ new.r = (sp00->r + sp01->r + sp10->r + sp11->r) / 4;
+ new.g = (sp00->g + sp01->g + sp10->g + sp11->g) / 4;
+ new.b = (sp00->b + sp01->b + sp10->b + sp11->b) / 4;
+ new.a = (sp00->a + sp01->a + sp10->a + sp11->a) / 4;
+
+ /* draw */
+ *dp = new;
+
+ /* advance source pointers */
+ sp += 2;
+
+ /* advance destination pointer */
+ dp++;
+ }
+
+ /* advance source pointer */
+ csp = (tColorRGBA *) ((Uint8 *) csp + 2 * src->pitch);
+
+ /* advance destination pointers */
+ dp = (tColorRGBA *) ((Uint8 *) dp + dgap);
+ }
+
+ return 0;
+}
+