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<?xml version="1.0" encoding="UTF-8"?>
<proposal href="proposals/WEBGL_blend_equation_advanced_coherent/">
<name>WEBGL_blend_equation_advanced_coherent</name>
<contact> <a href="https://www.khronos.org/webgl/public-mailing-list/">WebGL
working group</a> (public_webgl 'at' khronos.org) </contact>
<contributors>
<contributor>Ashley Gullen (ashley at scirra dot com)</contributor>
<contributor>Members of the WebGL working group</contributor>
</contributors>
<number>NN</number>
<depends>
<api version="1.0"/>
</depends>
<overview>
<mirrors href="https://www.opengl.org/registry/specs/KHR/blend_equation_advanced.txt"
name="KHR_blend_equation_advanced_coherent">
</mirrors>
<div class="nonnormative">
<p>This extension exposes the KHR_blend_equation_advanced_coherent functionality to WebGL.</p>
<p>CanvasRenderingContext2D provides a series of common blend functions with globalComposeOperation, such as "multiply" and "screen". KHR_blend_equation_advanced_coherent provides, with the exception of "xor", exactly the same list of blend functions for WebGL, as detailed below:</p>
<ul>
<li>"multiply": MULTIPLY_KHR</li>
<li>"screen": SCREEN_KHR</li>
<li>"overlay": OVERLAY_KHR</li>
<li>"darken": DARKEN_KHR</li>
<li>"lighten": LIGHTEN_KHR</li>
<li>"color-dodge": COLORDODGE_KHR</li>
<li>"color-burn": COLORBURN_KHR</li>
<li>"hard-light": HARDLIGHT_KHR</li>
<li>"soft-light": SOFTLIGHT_KHR</li>
<li>"difference": DIFFERENCE_KHR</li>
<li>"exclusion": EXCLUSION_KHR</li>
<li>"hue": HSL_HUE_KHR</li>
<li>"saturation": HSL_SATURATION_KHR</li>
<li>"color": HSL_COLOR_KHR</li>
<li>"luminosity": HSL_LUMINOSITY_KHR</li>
</ul>
<p>These effects are useful for high-quality artistic blends. They can be implemented using shaders and rendering via an intermediate texture. However this has a high performance overhead both in draw calls and GPU bandwidth. Advanced blend modes allow a much simpler, high-performance way of implementing these blends. Using shaders rendering to an intermediate texture can be used as a fallback if this extension is not supported.</p>
<p>Note only the coherent variant of this extension is exposed in order to eliminate the possibility of undefined behavior in KHR_blend_equation_advanced. This also simplifies the extension and removes the need to insert blend barriers during rendering.</p>
</div>
<features>
<feature>The <code>blendEquation</code> entry point is extended to accept the enums in the IDL below</feature>
</features>
</overview>
<idl xml:space="preserve">
[NoInterfaceObject]
interface WEBGL_blend_equation_advanced_coherent {
const GLenum MULTIPLY = 0x9294;
const GLenum SCREEN = 0x9295;
const GLenum OVERLAY = 0x9296;
const GLenum DARKEN = 0x9297;
const GLenum LIGHTEN = 0x9298;
const GLenum COLORDODGE = 0x9299;
const GLenum COLORBURN = 0x929A;
const GLenum HARDLIGHT = 0x929B;
const GLenum SOFTLIGHT = 0x929C;
const GLenum DIFFERENCE = 0x929E;
const GLenum EXCLUSION = 0x92A0;
const GLenum HSL_HUE = 0x92AD;
const GLenum HSL_SATURATION = 0x92AE;
const GLenum HSL_COLOR = 0x92AF;
const GLenum HSL_LUMINOSITY = 0x92B0;
};
</idl>
<security/>
<ipstatus/>
<additions/>
<!-- Additions to the WebGL Specification -->
<errors/>
<newstate/>
<newimplstate/>
<!-- New Implementation-Dependent State -->
<samplecode xml:space="preserve">
<pre>
var ext = gl.getExtension("WEBGL_blend_equation_advanced_coherent");
gl.blendEquation(ext.MULTIPLY);
gl.getParameter(gl.BLEND_EQUATION) == ext.MULTIPLY;
</pre>
</samplecode>
<tests/>
<issues/>
<history>
<revision date="2018/09/13">
<change>Forked from WEBGL_blend_equation_advanced to specify only the coherent variant</change>
</revision>
<revision date="2018/08/23">
<change>Converted to extension XML format</change>
</revision>
<revision date="2018/08/21">
<change>Revised description</change>
</revision>
<revision date="2015/05/26">
<change>Original draft as a TXT file</change>
</revision>
</history>
</proposal>
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