Fix graphics glitch with negative viewport coords.

2 files changed, 34 insertions, 15 deletions

diff --git a/src/area.c b/src/area.c
index ae8b071..674a81c 100644
--- a/src/area.c
+++ b/src/area.c
@@ -118,35 +118,54 @@ render_area_to_viewport(struct area *area, struct viewport *vp)
 
 void
 render_area_to_surface(struct area *area, SDL_Rect *arearect,
-		SDL_Surface *dst, SDL_Rect *dstrect)
+		SDL_Surface *surface, SDL_Rect *surfacerect)
 {
-	debug("Rendering %dx%d area rect at (%d,%d) "
-			"onto %dx%d surface rect at (%d,%d)...",
-			arearect->w, arearect->h, arearect->x, arearect->y,
-			dstrect->w, dstrect->h, dstrect->x, dstrect->y);
+	SDL_Rect srcrect, dstrect;
+
+	memcpy(&srcrect, arearect, sizeof(srcrect));
+	memcpy(&dstrect, surfacerect, sizeof(dstrect));
 
 	/* Fast fill with black to avoid artifacts in off-map pixels. */
 	/* NB: This is gray, at least temporarily. */
-	SDL_FillRect(dst, dstrect, SDL_MapRGB(dst->format, 63, 63, 63));
+	SDL_FillRect(surface, &dstrect,
+			SDL_MapRGB(surface->format, 63, 63, 63));
+
+	/* Avoid fun glitches due to negative coordinates in source
+	 * rectangles. */
+	if (srcrect.x < 0) {
+		srcrect.x = 0;
+		dstrect.x = surfacerect->x - arearect->x;
+	}
+	if (srcrect.y < 0) {
+		srcrect.y = 0;
+		dstrect.y = surfacerect->y - arearect->y;
+	}
+
+#if 0
+	debug("Rendering %dx%d area rect at (%d,%d) "
+			"onto %dx%d surface rect at (%d,%d)...",
+			srcrect.w, srcrect.h, srcrect.x, srcrect.y,
+			dstrect.w, dstrect.h, dstrect.x, dstrect.y);
+#endif
 
 	/* Blit ground layer. */
-	SDL_BlitSurface(area->map_layers[AREA_LAYER_GROUND], arearect,
-			dst, dstrect);
+	SDL_BlitSurface(area->map_layers[AREA_LAYER_GROUND], &srcrect,
+			surface, &dstrect);
 
 	/* Blit low objects layer. */
-	SDL_BlitSurface(area->map_layers[AREA_LAYER_OBJ_LOW], arearect,
-			dst, dstrect);
+	SDL_BlitSurface(area->map_layers[AREA_LAYER_OBJ_LOW], &srcrect,
+			surface, &dstrect);
 /*	return;*/
 
 	/* TODO: Blit low sprites. */
 
 	/* Blit middle objects layer. */
-	SDL_BlitSurface(area->map_layers[AREA_LAYER_OBJ_MID], arearect,
-			dst, dstrect);
+	SDL_BlitSurface(area->map_layers[AREA_LAYER_OBJ_MID], &srcrect,
+			surface, &dstrect);
 
 	/* TODO: Blit high sprites. */
 
 	/* Blit high objects layer. */
-	SDL_BlitSurface(area->map_layers[AREA_LAYER_OBJ_HIGH], arearect,
-			dst, dstrect);
+	SDL_BlitSurface(area->map_layers[AREA_LAYER_OBJ_HIGH], &srcrect,
+			surface, &dstrect);
 }
diff --git a/src/area.h b/src/area.h
index a1b7e92..aaddf1f 100644
--- a/src/area.h
+++ b/src/area.h
@@ -13,6 +13,6 @@ struct area {
 struct area *area_new(struct map *map);
 void render_area_to_viewport(struct area *area, struct viewport *vp);
 void render_area_to_surface(struct area *area, SDL_Rect *arearect,
-		SDL_Surface *dst, SDL_Rect *dstrect);
+		SDL_Surface *surface, SDL_Rect *surfacerect);
 
 #endif