ogc: avoid rounding issues with texture drawing

Author: mardy

src/video/ogc/SDL_ogcgxcommon.c

@@ -59,7 +59,13 @@ void OGC_draw_init(int w, int h)
     SDL_LogDebug(SDL_LOG_CATEGORY_VIDEO, "OGC_draw_init called with %d, %d", w, h);
 
     guMtxIdentity(mv);
-    guMtxTransApply(mv, mv, 0.5, 0.5, 0);
+    /* Ideally we would use 0.5 to center the coordinates on the pixels, but
+     * this causes some visual artifacts due to rounding: in the VVVVVV game,
+     * all 8x8 pixel textures lose their rightmost column and bottom row,
+     * except when they are drawn on the bottom-right quadrant of the screen.
+     * Values from 0.1 to 0.4 fix this issue, while preserving pixel accuracy
+     * on drawing operations. */
+    guMtxTransApply(mv, mv, 0.4, 0.4, 0);
     GX_LoadPosMtxImm(mv, GX_PNMTX0);
 
     GX_ClearVtxDesc();