1 files changed, 62 insertions, 0 deletions
diff --git a/layout/reftests/css-blending/background-blending-alpha-ref.html b/layout/reftests/css-blending/background-blending-alpha-ref.html
new file mode 100644
index 000000000..6a7055938
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+++ b/layout/reftests/css-blending/background-blending-alpha-ref.html
@@ -0,0 +1,62 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<style>
+.reftest {
+  background-color: rgba(0, 255, 0, 0.5);
+}
+
+.child {
+  width: 100px;
+  height: 100px;
+  opacity: 0.5;
+  background-color: rgb(0, 127, 0);
+}
+
+.topleft {
+  float:left;
+
+  width: 100px;
+  height: 100px;
+
+  /*First blend black rect with green in place*/
+  /* Cs = (1 - αb) x Cs + αb x B(Cb, Cs)*/
+  /* B(Cb, Cs) = | Cb - Cs | = (0, 0, 0) */
+  /* 0.5 * (0, 255, 0) + 0.5 * (0, 0, 0) = (0, 127.5, 0)*/
+
+  /* Now, composite the resulting color with src-over; the alpha is the original alpha for the top layer
+    while the color is the blending result*/
+  /* co = αs x Fa x Cs + αb x Fb x Cb  - this is premultiplied */
+  /* αo = αs + αb x (1 – αs) */
+  /* Source over:     Fa = 1; Fb = 1 – αs */
+  /*co = 0.5 * 1 * (0, 127.5, 0) + 0.5 * 0.5 * (0, 255, 0) = (0, 63.5, 0) + 0.25 * (0, 255, 0) = (0, 127.5, 0)*/
+  /*ao = 0.5 + 0.5 * 0.5 = 0.75*/
+  /* Co = co/ao = (0, 127.5, 0) / 0.75*/
+
+  /* Now alpha composite on white background */
+  /*co = 0.75 * 1 * (0, 127.5, 0) / 0.75 + 1 * 0.25 * (255, 255, 255) = (0, 127.5, 0) + (63.75, 63.75, 63.75) = (63.75, 159, 63.75) = (64, 191, 64) */
+
+  background-color: rgb(64, 191, 64);
+}
+
+.topright {
+  float:left;
+  width: 100px;
+  height: 100px;
+}
+
+.bottom {
+  width:200px;
+  height: 100px;
+  clear:both;
+}
+
+</style>
+
+<div class="topleft"></div>
+<div class="reftest topright"></div>
+<div class="reftest bottom"></div>
+
+</html>