63 lines
1.5 KiB
HTML
63 lines
1.5 KiB
HTML
<!--
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Any copyright is dedicated to the Public Domain.
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http://creativecommons.org/publicdomain/zero/1.0/
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-->
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<html>
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<style>
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.reftest {
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background-color: rgba(0, 255, 0, 0.5);
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}
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.child {
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width: 100px;
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height: 100px;
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opacity: 0.5;
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background-color: rgb(0, 127, 0);
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}
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.topleft {
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float:left;
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width: 100px;
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height: 100px;
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/*First blend black rect with green in place*/
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/* Cs = (1 - αb) x Cs + αb x B(Cb, Cs)*/
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/* B(Cb, Cs) = | Cb - Cs | = (0, 0, 0) */
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/* 0.5 * (0, 255, 0) + 0.5 * (0, 0, 0) = (0, 127.5, 0)*/
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/* Now, composite the resulting color with src-over; the alpha is the original alpha for the top layer
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while the color is the blending result*/
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/* co = αs x Fa x Cs + αb x Fb x Cb - this is premultiplied */
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/* αo = αs + αb x (1 – αs) */
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/* Source over: Fa = 1; Fb = 1 – αs */
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/*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)*/
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/*ao = 0.5 + 0.5 * 0.5 = 0.75*/
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/* Co = co/ao = (0, 127.5, 0) / 0.75*/
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/* Now alpha composite on white background */
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/*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) */
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background-color: rgb(64, 191, 64);
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}
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.topright {
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float:left;
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width: 100px;
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height: 100px;
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}
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.bottom {
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width:200px;
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height: 100px;
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clear:both;
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}
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</style>
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<div class="topleft"></div>
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<div class="reftest topright"></div>
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<div class="reftest bottom"></div>
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</html>
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