[gtk+] cssvalue: Change color transitions to run premultiplied

[Benjamin Otte <otte src gnome org>]

commit cd3f24d5793e038ee29d780b24747707c73ad00c
Author: Benjamin Otte <otte redhat com>
Date:   Fri Jun 26 21:08:04 2015 +0200

    cssvalue: Change color transitions to run premultiplied
    
    Previously, the unpremultiplied values from the GdkRGBA were taken. Now
    we premultiply the color values as specified by the CSS specs.
    This is only relevant when transitioning with translucent colors.
    
    An example is the halfway transition between transparent (0, 0, 0, 0)
    and white (1, 1, 1, 1). Previously, all 4 values where transitioned
    separately and the result was semi-transparent gray (0.5, 0.5, 0.5,
    0.5).
    By depending on the alpha value, the result is now semi-transparent
    white (1, 1, 1, 0.5) which is what one would naively expect.
    
    New reftest: color-transition

 gtk/gtkcssrgbavalue.c                      |   12 +++++++++---
 testsuite/reftests/Makefile.am             |    3 +++
 testsuite/reftests/color-transition.css    |   18 ++++++++++++++++++
 testsuite/reftests/color-transition.ref.ui |    8 ++++++++
 testsuite/reftests/color-transition.ui     |   25 +++++++++++++++++++++++++
 5 files changed, 63 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkcssrgbavalue.c b/gtk/gtkcssrgbavalue.c
index 0b66f8a..7005347 100644
--- a/gtk/gtkcssrgbavalue.c
+++ b/gtk/gtkcssrgbavalue.c
@@ -74,9 +74,15 @@ gtk_css_value_rgba_transition (GtkCssValue *start,
     }
   else
     {
-      result.red = transition (start->rgba.red, end->rgba.red, progress);
-      result.green = transition (start->rgba.green, end->rgba.green, progress);
-      result.blue = transition (start->rgba.blue, end->rgba.blue, progress);
+      result.red = transition (start->rgba.red * start->rgba.alpha,
+                               end->rgba.red * end->rgba.alpha,
+                               progress) / result.alpha;
+      result.green = transition (start->rgba.green * start->rgba.alpha,
+                                 end->rgba.green * end->rgba.alpha,
+                                 progress) / result.alpha;
+      result.blue = transition (start->rgba.blue * start->rgba.alpha,
+                                end->rgba.blue * end->rgba.alpha,
+                                progress) / result.alpha;
     }
 
   return _gtk_css_rgba_value_new_from_rgba (&result);
diff --git a/testsuite/reftests/Makefile.am b/testsuite/reftests/Makefile.am
index 61cc0a2..3887acc 100644
--- a/testsuite/reftests/Makefile.am
+++ b/testsuite/reftests/Makefile.am
@@ -185,6 +185,9 @@ testdata = \
        cellrenderer-pixbuf-stock-rtl.css \
        cellrenderer-pixbuf-stock-rtl.ui \
        cellrenderer-pixbuf-stock-rtl.ref.ui \
+       color-transition.css \
+       color-transition.ref.ui \
+       color-transition.ui \
        css-currentcolor-alpha.css \
        css-currentcolor-alpha.ui \
        css-currentcolor-alpha.ref.ui \
diff --git a/testsuite/reftests/color-transition.css b/testsuite/reftests/color-transition.css
new file mode 100644
index 0000000..ac964b0
--- /dev/null
+++ b/testsuite/reftests/color-transition.css
@@ -0,0 +1,18 @@
+ import "reset-to-defaults.css";
+
+ keyframes foo {
+  100% { background-color: blue; }
+}
+
+GtkWindow {
+  background-color: #7F0080;
+}
+
+GtkBox {
+  background-color: red;
+}
+
+GtkBox GtkBox {
+  background-color: transparent;
+  animation: foo 100s steps(2);
+}
diff --git a/testsuite/reftests/color-transition.ref.ui b/testsuite/reftests/color-transition.ref.ui
new file mode 100644
index 0000000..fa28350
--- /dev/null
+++ b/testsuite/reftests/color-transition.ref.ui
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <!-- interface-requires gtk+ 3.0 -->
+  <object class="GtkWindow" id="window1">
+    <property name="can_focus">False</property>
+    <property name="type">popup</property>
+  </object>
+</interface>
diff --git a/testsuite/reftests/color-transition.ui b/testsuite/reftests/color-transition.ui
new file mode 100644
index 0000000..47e01cb
--- /dev/null
+++ b/testsuite/reftests/color-transition.ui
@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <!-- interface-requires gtk+ 3.0 -->
+  <object class="GtkWindow" id="window1">
+    <property name="can_focus">False</property>
+    <property name="type">popup</property>
+    <child>
+      <object class="GtkBox" id="box1">
+        <property name="visible">True</property>
+        <property name="can_focus">False</property>
+        <child>
+          <object class="GtkBox" id="box2">
+            <property name="visible">True</property>
+            <property name="can_focus">False</property>
+            <property name="hexpand">True</property>
+            <property name="vexpand">True</property>
+            <child>
+              <placeholder/>
+            </child>
+          </object>
+        </child>
+      </object>
+    </child>
+  </object>
+</interface>