Software nearest scaling: start at the middle of pixel

so that it matches opengl GL_NEAREST mode most of the time

src/video/SDL_blit_slow.c

@@ -49,15 +49,15 @@ SDL_Blit_Slow(SDL_BlitInfo * info)
     Uint32 rgbmask = ~src_fmt->Amask;
     Uint32 ckey = info->colorkey & rgbmask;
 
-    posy = 0;
     incy = (info->src_h << 16) / info->dst_h;
     incx = (info->src_w << 16) / info->dst_w;
+    posy = incy / 2; /* start at the middle of pixel */
 
     while (info->dst_h--) {
         Uint8 *src = 0;
         Uint8 *dst = info->dst;
         int n = info->dst_w;
-        posx = 0;
+        posx = incx / 2; /* start at the middle of pixel */
         srcy = posy >> 16;
         while (n--) {
             srcx = posx >> 16;

src/video/SDL_stretch.c

@@ -857,13 +857,13 @@ SDL_LowerSoftStretchLinear(SDL_Surface *s, const SDL_Rect *srcrect,
     incy = (src_h << 16) / dst_h;                                                       \
     incx = (src_w << 16) / dst_w;                                                       \
     dst_gap   = dst_pitch - bpp * dst_w;                                                \
-    posy = 0;                                                                           \
+    posy = incy / 2;                                                                    \
 
 #define SDL_SCALE_NEAREST__HEIGHT                                                       \
     srcy = (posy >> 16);                                                                \
     src_h0  = (const Uint32 *)((const Uint8 *)src_ptr + srcy * src_pitch);              \
     posy += incy;                                                                       \
-    posx = 0;                                                                           \
+    posx = incx / 2;                                                                    \
     n = dst_w;
 
 

src/video/sdlgenblit.pl

@@ -458,15 +458,15 @@ __EOF__
 
     print FILE <<__EOF__;
 
-    posy = 0;
     incy = (info->src_h << 16) / info->dst_h;
     incx = (info->src_w << 16) / info->dst_w;
+    posy = incy / 2;
 
     while (info->dst_h--) {
         $format_type{$src} *src = 0;
         $format_type{$dst} *dst = ($format_type{$dst} *)info->dst;
         int n = info->dst_w;
-        posx = 0;
+        posx = incx / 2;
 
         srcy = posy >> 16;
         while (n--) {