Revert back screen centering when using c2p

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401102

src/video/xbios/SDL_xbios.c

@@ -724,8 +724,17 @@ static void XBIOS_UpdateRects(_THIS, int numrects, SDL_Rect *rects)
 	surface = this->screen;
 
 	if ((surface->format->BitsPerPixel) == 8) {
+		void *destscr;
+		int destx;
 		int i;
 
+		/* Center on destination screen */
+		destscr = XBIOS_screens[XBIOS_fbnum];
+		destscr += XBIOS_pitch * ((XBIOS_height - surface->h) >> 1);
+		destx = (XBIOS_width - surface->w) >> 1;
+		destx &= ~15;
+		destscr += destx;
+
 		for (i=0;i<numrects;i++) {
 			void *source,*destination;
 			int x1,x2;
@@ -740,16 +749,19 @@ static void XBIOS_UpdateRects(_THIS, int numrects, SDL_Rect *rects)
 			source += surface->pitch * rects[i].y;
 			source += x1;
 
-			destination = XBIOS_screens[XBIOS_fbnum];
+			destination = destscr;
 			destination += XBIOS_pitch * rects[i].y;
 			destination += x1;
 
 			/* Convert chunky to planar screen */
 			SDL_Atari_C2pConvert(
-				source, destination,
-				x2-x1, rects[i].h,
+				source,
+				destination,
+				x2-x1,
+				rects[i].h,
 				XBIOS_doubleline,
-				surface->pitch, XBIOS_pitch
+				surface->pitch,
+				XBIOS_pitch
 			);
 		}
 	}
@@ -770,12 +782,25 @@ static void XBIOS_UpdateRects(_THIS, int numrects, SDL_Rect *rects)
 static int XBIOS_FlipHWSurface(_THIS, SDL_Surface *surface)
 {
 	if ((surface->format->BitsPerPixel) == 8) {
+		void *destscr;
+		int destx;
+			
+		/* Center on destination screen */
+		destscr = XBIOS_screens[XBIOS_fbnum];
+		destscr += XBIOS_pitch * ((XBIOS_height - surface->h) >> 1);
+		destx = (XBIOS_width - surface->w) >> 1;
+		destx &= ~15;
+		destscr += destx;
+
 		/* Convert chunky to planar screen */
 		SDL_Atari_C2pConvert(
-			surface->pixels, XBIOS_screens[XBIOS_fbnum],
-			surface->w, surface->h,
+			surface->pixels,
+			destscr,
+			surface->w,
+			surface->h,
 			XBIOS_doubleline,
-			surface->pitch, XBIOS_pitch
+			surface->pitch,
+			XBIOS_pitch
 		);
 	}