From dfa2544f158930b002df74e676f3ef7aeeee1bd4 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 13 May 2010 09:52:39 +0100
Subject: [PATCH] color: Special case comparing color stops.

color stops are not premultiplied so we need to handle them carefully
when comparing. The next step will be to make cairo_color_stop_t a
unique type to prevent this mistake again.
---
 src/cairo-color.c         | 30 ++++++++++++++++++++++++++++++
 src/cairo-gl-surface.c    |  4 ++--
 src/cairo-gstate.c        |  4 ++--
 src/cairo-pattern.c       |  6 +++---
 src/cairoint.h            |  4 ++++
 src/drm/cairo-drm-intel.c |  2 +-
 6 files changed, 42 insertions(+), 8 deletions(-)

diff --git a/src/cairo-color.c b/src/cairo-color.c
index 1df82bbe4..d6c6c3d9f 100644
--- a/src/cairo-color.c
+++ b/src/cairo-color.c
@@ -174,3 +174,33 @@ _cairo_color_equal (const cairo_color_t *color_a,
            color_a->blue_short  == color_b->blue_short  &&
            color_a->alpha_short == color_b->alpha_short;
 }
+
+cairo_bool_t
+_cairo_color_stop_equal (const cairo_color_t *color_a,
+			 const cairo_color_t *color_b)
+{
+    uint16_t a, b;
+
+    if (color_a == color_b)
+	return TRUE;
+
+    if (color_a->alpha_short != color_b->alpha_short)
+	return FALSE;
+
+    a   = _cairo_color_double_to_short (color_a->red   * color_a->alpha);
+    b   = _cairo_color_double_to_short (color_b->red   * color_b->alpha);
+    if (a != b)
+	return FALSE;
+
+    a   = _cairo_color_double_to_short (color_a->green   * color_a->alpha);
+    b   = _cairo_color_double_to_short (color_b->green   * color_b->alpha);
+    if (a != b)
+	return FALSE;
+
+    a   = _cairo_color_double_to_short (color_a->blue   * color_a->alpha);
+    b   = _cairo_color_double_to_short (color_b->blue   * color_b->alpha);
+    if (a != b)
+	return FALSE;
+
+    return TRUE;
+}
diff --git a/src/cairo-gl-surface.c b/src/cairo-gl-surface.c
index 82a398181..27fc02c77 100644
--- a/src/cairo-gl-surface.c
+++ b/src/cairo-gl-surface.c
@@ -1253,8 +1253,8 @@ _cairo_gl_gradient_operand_init(cairo_gl_context_t *ctx,
 	 * Happens more often than you would believe.
 	 */
 	for (i = 1; i < gradient->n_stops; i++) {
-	    if (! _cairo_color_equal (&gradient->stops[0].color,
-				      &gradient->stops[i].color))
+	    if (! _cairo_color_stop_equal (&gradient->stops[0].color,
+					   &gradient->stops[i].color))
 		{
 		    break;
 		}
diff --git a/src/cairo-gstate.c b/src/cairo-gstate.c
index 78aab5080..c3f63db10 100644
--- a/src/cairo-gstate.c
+++ b/src/cairo-gstate.c
@@ -887,8 +887,8 @@ _cairo_gstate_copy_pattern (cairo_pattern_t *pattern,
 		 * Happens more often than you would believe.
 		 */
 		for (i = 1; i < src->n_stops; i++) {
-		    if (! _cairo_color_equal (&src->stops[0].color,
-					      &src->stops[i].color))
+		    if (! _cairo_color_stop_equal (&src->stops[0].color,
+						   &src->stops[i].color))
 		    {
 			break;
 		    }
diff --git a/src/cairo-pattern.c b/src/cairo-pattern.c
index 85045270a..2fea11a2e 100644
--- a/src/cairo-pattern.c
+++ b/src/cairo-pattern.c
@@ -2294,8 +2294,8 @@ _cairo_pattern_acquire_surface (const cairo_pattern_t	   *pattern,
 	     * Happens more often than you would believe.
 	     */
 	    for (i = 1; i < src->n_stops; i++) {
-		if (! _cairo_color_equal (&src->stops[0].color,
-					  &src->stops[i].color))
+		if (! _cairo_color_stop_equal (&src->stops[0].color,
+					       &src->stops[i].color))
 		{
 		    break;
 		}
@@ -2767,7 +2767,7 @@ _cairo_gradient_color_stops_equal (const cairo_gradient_pattern_t *a,
     for (n = 0; n < a->n_stops; n++) {
 	if (a->stops[n].offset != b->stops[n].offset)
 	    return FALSE;
-	if (! _cairo_color_equal (&a->stops[n].color, &b->stops[n].color))
+	if (! _cairo_color_stop_equal (&a->stops[n].color, &b->stops[n].color))
 	    return FALSE;
     }
 
diff --git a/src/cairoint.h b/src/cairoint.h
index 5cf0bcf7b..6fe370294 100644
--- a/src/cairoint.h
+++ b/src/cairoint.h
@@ -1309,6 +1309,10 @@ cairo_private cairo_bool_t
 _cairo_color_equal (const cairo_color_t *color_a,
                     const cairo_color_t *color_b) cairo_pure;
 
+cairo_private cairo_bool_t
+_cairo_color_stop_equal (const cairo_color_t *color_a,
+			 const cairo_color_t *color_b) cairo_pure;
+
 /* cairo-font-face.c */
 
 extern const cairo_private cairo_font_face_t _cairo_font_face_nil;
diff --git a/src/drm/cairo-drm-intel.c b/src/drm/cairo-drm-intel.c
index 4d69f8ab6..032647c39 100644
--- a/src/drm/cairo-drm-intel.c
+++ b/src/drm/cairo-drm-intel.c
@@ -1421,7 +1421,7 @@ _gradient_color_stops_equal (const cairo_gradient_pattern_t *a,
 	    return FALSE;
 	}
 
-	if (! _cairo_color_equal (&a->stops[n].color, &b->stops[n].color))
+	if (! _cairo_color_stop_equal (&a->stops[n].color, &b->stops[n].color))
 	    return FALSE;
     }