gdi-RGB24-ARGB32.patch

changeset:   106848:28db6dbdd9ea
tag:         gdi-patch
tag:         qbase
tag:         qtip
tag:         tip
user:        Jeff Muizelaar <jmuizelaar@mozilla.com>
date:        Wed Sep 12 22:52:06 2012 -0400
summary:     Bug 788794. Use BitBlt to do SOURCE and OVER from RGB24 to ARGB32. r=nical

diff --git a/gfx/cairo/cairo/src/cairo-win32-surface.c b/gfx/cairo/cairo/src/cairo-win32-surface.c
--- a/gfx/cairo/cairo/src/cairo-win32-surface.c
+++ b/gfx/cairo/cairo/src/cairo-win32-surface.c
@@ -884,16 +884,28 @@ static cairo_int_status_t
 		      src_x, src_y,
 		      src_w, src_h,
 		      blend_function))
 	return _cairo_win32_print_gdi_error ("_cairo_win32_surface_composite(AlphaBlend)");
 
     return CAIRO_STATUS_SUCCESS;
 }
 
+/* makes the alpha channel in a RGB24 surface 0xff */
+static void
+make_opaque (cairo_image_surface_t *image, cairo_rectangle_int_t src_r)
+{
+    int x; int y;
+    for (y = src_r.y; y < src_r.height; y++) {
+        for (x = src_r.x; x < src_r.width; x++) {
+            image->data[y * image->stride + x*4 + 3] = 0xff;
+        }
+    }
+}
+
 static cairo_int_status_t
 _cairo_win32_surface_composite_inner (cairo_win32_surface_t *src,
 				      cairo_image_surface_t *src_image,
 				      cairo_win32_surface_t *dst,
 				      cairo_rectangle_int_t src_extents,
 				      cairo_rectangle_int_t src_r,
 				      cairo_rectangle_int_t dst_r,
 				      int alpha,
@@ -935,16 +947,24 @@ static cairo_int_status_t
 				src_r.width, - (int) src_r.height,
 				src_image->data,
 				&bi,
 				DIB_RGB_COLORS,
 				SRCCOPY))
 		return _cairo_win32_print_gdi_error ("_cairo_win32_surface_composite(StretchDIBits)");
 	}
     } else if (!needs_alpha) {
+	if (src->format == CAIRO_FORMAT_RGB24 && dst->format == CAIRO_FORMAT_ARGB32) {
+	    /* Because we store RGB24 & ARGB32 in the same way GDI has no way
+	     * to ignore the alpha channel from a RGB24 source. Therefore, we set
+	     * the alpha channel in our RGB24 source to opaque so that we can treat
+	     * it like ARGB32. */
+	    GdiFlush();
+	    make_opaque(src->image, src_r);
+	}
 	/* BitBlt or StretchBlt? */
 	if (!needs_scale && (dst->flags & CAIRO_WIN32_SURFACE_CAN_BITBLT)) {
             if (!BitBlt (dst->dc,
 			 dst_r.x, dst_r.y,
 			 dst_r.width, dst_r.height,
 			 src->dc,
 			 src_r.x, src_r.y,
 			 SRCCOPY))
@@ -1184,28 +1204,36 @@ static cairo_int_status_t
 	}
     } else {
 	needs_repeat = TRUE;
     }
 
     /*
      * Operations that we can do:
      *
+     * AlphaBlend uses the following formula for alpha when not use the per-pixel alpha (AlphaFormat = 0)
+     *   Dst.Alpha = Src.Alpha * (SCA/255.0) + Dst.Alpha * (1.0 - (SCA/255.0))
+     * This turns into Dst.Alpha = Src.Alpha when SCA = 255.
+     * (http://msdn.microsoft.com/en-us/library/aa921335.aspx)
+     *
      *  RGB OVER  RGB -> BitBlt (same as SOURCE)
-     *  RGB OVER ARGB -> UNSUPPORTED (AlphaBlend treats this as a BitBlt, even with SCA 255 and no AC_SRC_ALPHA)
+     *  RGB OVER ARGB -> Partially supported, We convert this operation into a ARGB SOURCE ARGB
+     *                   by setting the alpha values of the source to 255.
      * ARGB OVER ARGB -> AlphaBlend, with AC_SRC_ALPHA
      * ARGB OVER  RGB -> AlphaBlend, with AC_SRC_ALPHA; we'll have junk in the dst A byte
      * 
      *  RGB OVER  RGB + mask -> AlphaBlend, no AC_SRC_ALPHA
-     *  RGB OVER ARGB + mask -> UNSUPPORTED
+     *  RGB OVER ARGB + mask -> Partially supported, We convert this operation into a ARGB OVER ARGB + mask
+     *                          by setting the alpha values of the source to 255.
      * ARGB OVER ARGB + mask -> AlphaBlend, with AC_SRC_ALPHA
      * ARGB OVER  RGB + mask -> AlphaBlend, with AC_SRC_ALPHA; junk in the dst A byte
      * 
      *  RGB SOURCE  RGB -> BitBlt
-     *  RGB SOURCE ARGB -> UNSUPPORTED (AlphaBlend treats this as a BitBlt, even with SCA 255 and no AC_SRC_ALPHA)
+     *  RGB SOURCE ARGB -> Partially supported, We convert this operation into a ARGB SOURCE ARGB
+     *                     by setting the alpha values of the source to 255.
      * ARGB SOURCE ARGB -> BitBlt
      * ARGB SOURCE  RGB -> BitBlt
      * 
      *  RGB SOURCE  RGB + mask -> unsupported
      *  RGB SOURCE ARGB + mask -> unsupported
      * ARGB SOURCE ARGB + mask -> unsupported
      * ARGB SOURCE  RGB + mask -> unsupported
      */
@@ -1222,22 +1250,32 @@ static cairo_int_status_t
 		needs_alpha = FALSE;
 	    } else {
 		needs_alpha = TRUE;
 	    }
 	} else if (src_format == CAIRO_FORMAT_ARGB32 &&
 		   dst->format == CAIRO_FORMAT_RGB24)
 	{
 	    needs_alpha = TRUE;
+	} else if (src_format == CAIRO_FORMAT_RGB24 &&
+		   dst->format == CAIRO_FORMAT_ARGB32 &&
+		   src->image)
+	{
+	    if (alpha == 255) {
+		needs_alpha = FALSE;
+	    } else {
+		needs_alpha = TRUE;
+	    }
 	} else {
 	    goto UNSUPPORTED;
 	}
     } else if (alpha == 255 && op == CAIRO_OPERATOR_SOURCE) {
 	if ((src_format == dst->format) ||
-	    (src_format == CAIRO_FORMAT_ARGB32 && dst->format == CAIRO_FORMAT_RGB24))
+	    (src_format == CAIRO_FORMAT_ARGB32 && dst->format == CAIRO_FORMAT_RGB24) ||
+	    (src_format == CAIRO_FORMAT_RGB24  && dst->format == CAIRO_FORMAT_ARGB32 && src->image))
 	{
 	    needs_alpha = FALSE;
 	} else {
 	    goto UNSUPPORTED;
 	}
     } else {
 	goto UNSUPPORTED;
     }