[gtk] spoof proof infobars, take 2

This looks like a big review, but a lot of it is just shuffling code around:
- rip out dropshadow code
- move arrow state and drawing to a model class, to allow sharing between BrowserWindow and Infobar
- get rid of InfoBar's border_bin_ and slightly simplify baseclasses by no longer requiring them to call show() on the toplevel widget

Added stuff:
- transition between arrow colors (previous_color_ vs. target_color_ business)
- arrows protruding on neighboring infobars

BUG=48996
TEST=manual, with animations slowed down 100x

Review URL: http://codereview.chromium.org/3919004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@63956 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 45 insertions, 10 deletions

diff --git a/gfx/color_utils.cc b/gfx/color_utils.cc
index 268f556..73c585b 100644
--- a/gfx/color_utils.cc
+++ b/gfx/color_utils.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -256,13 +256,28 @@ SkColor AlphaBlend(SkColor foreground, SkColor background, SkAlpha alpha) {
     return background;
   if (alpha == 255)
     return foreground;
-  return SkColorSetRGB(
-    ((SkColorGetR(foreground) * alpha) +
-     (SkColorGetR(background) * (255 - alpha))) / 255,
-    ((SkColorGetG(foreground) * alpha) +
-     (SkColorGetG(background) * (255 - alpha))) / 255,
-    ((SkColorGetB(foreground) * alpha) +
-     (SkColorGetB(background) * (255 - alpha))) / 255);
+
+  int f_alpha = SkColorGetA(foreground);
+  int b_alpha = SkColorGetA(background);
+
+  double normalizer = (f_alpha * alpha + b_alpha * (255 - alpha)) / 255.0;
+  if (normalizer == 0.0)
+    return SkColorSetARGB(0, 0, 0, 0);
+
+  double f_weight = f_alpha * alpha / normalizer;
+  double b_weight = b_alpha * (255 - alpha) / normalizer;
+
+  double r = (SkColorGetR(foreground) * f_weight +
+              SkColorGetR(background) * b_weight) / 255.0;
+  double g = (SkColorGetG(foreground) * f_weight +
+              SkColorGetG(background) * b_weight) / 255.0;
+  double b = (SkColorGetB(foreground) * f_weight +
+              SkColorGetB(background) * b_weight) / 255.0;
+
+  return SkColorSetARGB(static_cast<int>(normalizer),
+                        static_cast<int>(r),
+                        static_cast<int>(g),
+                        static_cast<int>(b));
 }
 
 SkColor GetReadableColor(SkColor foreground, SkColor background) {
diff --git a/gfx/color_utils.h b/gfx/color_utils.h
index f511168..b6eb2da 100644
--- a/gfx/color_utils.h
+++ b/gfx/color_utils.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -58,7 +58,9 @@ SkColor GetAverageColorOfFavicon(SkBitmap* bitmap, SkAlpha alpha);
 void BuildLumaHistogram(SkBitmap* bitmap, int histogram[256]);
 
 // Returns a blend of the supplied colors, ranging from |background| (for
-// |alpha| == 0) to |foreground| (for |alpha| == 255).
+// |alpha| == 0) to |foreground| (for |alpha| == 255). The alpha channels of
+// the supplied colors are also taken into account, so the returned color may
+// be partially transparent.
 SkColor AlphaBlend(SkColor foreground, SkColor background, SkAlpha alpha);
 
 // Given a foreground and background color, try to return a foreground color
diff --git a/gfx/color_utils_unittest.cc b/gfx/color_utils_unittest.cc
index 363d700..30cf514 100644
--- a/gfx/color_utils_unittest.cc
+++ b/gfx/color_utils_unittest.cc
@@ -47,3 +47,21 @@ TEST(ColorUtils, ColorToHSLRegisterSpill) {
   EXPECT_EQ(153U, SkColorGetG(result));
   EXPECT_EQ(88U, SkColorGetB(result));
 }
+
+TEST(ColorUtils, AlphaBlend) {
+  SkColor fore = SkColorSetARGB(255, 200, 200, 200);
+  SkColor back = SkColorSetARGB(255, 100, 100, 100);
+
+  EXPECT_TRUE(color_utils::AlphaBlend(fore, back, 255) ==
+              fore);
+  EXPECT_TRUE(color_utils::AlphaBlend(fore, back, 0) ==
+              back);
+
+  // One is fully transparent, result is partially transparent.
+  back = SkColorSetA(back, 0);
+  EXPECT_EQ(136U, SkColorGetA(color_utils::AlphaBlend(fore, back, 136)));
+
+  // Both are fully transparent, result is fully transparent.
+  fore = SkColorSetA(fore, 0);
+  EXPECT_EQ(0U, SkColorGetA(color_utils::AlphaBlend(fore, back, 255)));
+}