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+<!--
+ 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>