Fix rendering of theme parts on Windows XP

It seems XP doesn't handle drawing non-alpha theme parts
on alpha destinations. We fix this by using alpha bitmaps only when
needed.

However this means any non-drawn area by the theme part is now draw
black, so we must take more care to only draw where the theme part draws,
so we find the theme part size when available.

gtk/gtkcssimagewin32.c

@@ -33,21 +33,23 @@ gtk_css_image_win32_draw (GtkCssImage        *image,
 {
   GtkCssImageWin32 *wimage = GTK_CSS_IMAGE_WIN32 (image);
   cairo_surface_t *surface;
+  int dx, dy;
 
   surface = _gtk_win32_theme_part_create_surface (wimage->theme, wimage->part, wimage->state, wimage->margins,
-						  width, height);
+						  width, height, &dx, &dy);
   
   if (wimage->state2 >= 0)
     {
       cairo_surface_t *surface2;
       cairo_t *cr;
+      int dx2, dy2;
 
       surface2 = _gtk_win32_theme_part_create_surface (wimage->theme, wimage->part2, wimage->state2, wimage->margins,
-						       width, height);
+						       width, height, &dx2, &dy2);
 
       cr = cairo_create (surface);
 
-      cairo_set_source_surface (cr, surface2, 0, 0);
+      cairo_set_source_surface (cr, surface2, dx2 - dx, dy2-dy);
       cairo_paint_with_alpha (cr, wimage->over_alpha);
       
       cairo_destroy (cr);
@@ -55,8 +57,8 @@ gtk_css_image_win32_draw (GtkCssImage        *image,
       cairo_surface_destroy (surface2);
     }
 
-  cairo_set_source_surface (cr, surface, 0, 0);
+  cairo_set_source_surface (cr, surface, dx, dy);
-  cairo_pattern_set_extend (cairo_get_source (cr), CAIRO_EXTEND_PAD);
+  cairo_pattern_set_extend (cairo_get_source (cr), CAIRO_EXTEND_NONE);
   cairo_rectangle (cr, 0, 0, width, height);
   cairo_fill (cr);
 

gtk/gtkwin32theme.c

@@ -184,27 +184,65 @@ _gtk_win32_theme_part_create_surface (HTHEME theme,
 				      int    state,
 				      int    margins[4],
 				      int    width,
-                                      int    height)
+                                      int    height,
+				      int   *x_offs_out,
+				      int   *y_offs_out)
 {
   cairo_surface_t *surface;
   GdkRGBA color;
   cairo_t *cr;
+  int x_offs;
+  int y_offs;
 #ifdef G_OS_WIN32
   HDC hdc;
   RECT rect;
+  SIZE size;
   HRESULT res;
+#endif
 
+  x_offs = margins[3];
+  y_offs = margins[0];
+
+  width -= margins[3] + margins[1];
+  height -= margins[0] + margins[2];
+
+#ifdef G_OS_WIN32
+  rect.left = 0;
+  rect.top = 0;
+  rect.right = width;
+  rect.bottom = height;
+
+  hdc = GetDC (NULL);
+  res = get_theme_part_size (theme, hdc, xp_part, state, &rect, 2, &size);
+  ReleaseDC (NULL, hdc);
+
+  if (res == S_OK)
+    {
+      x_offs += (width - size.cx) / 2;
+      y_offs += (height - size.cy) / 2;
+  
+      width = size.cx;
+      height = size.cy;
+
+      rect.right = width;
+      rect.bottom = height;
+    }
+
+  if (is_theme_partially_transparent (theme, xp_part, state))
     surface = cairo_win32_surface_create_with_dib (CAIRO_FORMAT_ARGB32, width, height);
+  else
+    surface = cairo_win32_surface_create_with_dib (CAIRO_FORMAT_RGB24, width, height);
+
   hdc = cairo_win32_surface_get_dc (surface);
 
-  rect.left = margins[3];
-  rect.top = margins[0];
-  rect.right = width - margins[1];
-  rect.bottom = height - margins[2];
-
   res = draw_theme_background (theme, hdc, xp_part, state, &rect, &rect);
+
+  *x_offs_out = x_offs;
+  *y_offs_out = y_offs;
+
   if (res == S_OK)
     return surface;
+
 #else /* !G_OS_WIN32 */
   surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, width, height);
 #endif /* G_OS_WIN32 */
@@ -218,6 +256,9 @@ _gtk_win32_theme_part_create_surface (HTHEME theme,
 
   cairo_destroy (cr);
   
+  *x_offs_out = x_offs;
+  *y_offs_out = y_offs;
+
   return surface;
 }
 

gtk/gtkwin32themeprivate.h

@@ -44,7 +44,9 @@ cairo_surface_t *  _gtk_win32_theme_part_create_surface  (HTHEME       theme,
                                                           int          state,
                                                           int          margins[4],
                                                           int          width,
-                                                          int          height);
+                                                          int          height,
+							  int         *x_offs_out,
+							  int         *y_offs_out);
 
 int                _gtk_win32_theme_int_parse     (GtkCssParser      *parser,
 						   GFile             *base,