Add EXT_blend_minmax extension

Author: Agamnentzar

README.md

@@ -218,6 +218,7 @@ Only the following for now:
 * [`OES_element_index_uint`](https://www.khronos.org/registry/webgl/extensions/OES_element_index_uint/)
 * [`OES_texture_float`](https://www.khronos.org/registry/webgl/extensions/OES_texture_float/)
 * [`WEBGL_draw_buffers`](https://www.khronos.org/registry/webgl/extensions/WEBGL_draw_buffers/)
+* [`EXT_blend_minmax`](https://www.khronos.org/registry/webgl/extensions/EXT_blend_minmax/)
 
 ### How can I keep up to date with what has changed in headless-gl?
 

src/javascript/extensions/ext-blend-minmax.js

@@ -0,0 +1,19 @@
+class EXTBlendMinMax {
+  constructor () {
+    this.MIN_EXT = 0x8007
+    this.MAX_EXT = 0x8008
+  }
+}
+
+function getEXTBlendMinMax (context) {
+  let result = null
+  const exts = context.getSupportedExtensions()
+
+  if (exts && exts.indexOf('EXT_blend_minmax') >= 0) {
+    result = new EXTBlendMinMax()
+  }
+
+  return result
+}
+
+module.exports = { getEXTBlendMinMax, EXTBlendMinMax }

src/javascript/webgl-rendering-context.js

@@ -9,6 +9,7 @@ const { getOESTextureFloat } = require('./extensions/oes-texture-float')
 const { getSTACKGLDestroyContext } = require('./extensions/stackgl-destroy-context')
 const { getSTACKGLResizeDrawingBuffer } = require('./extensions/stackgl-resize-drawing-buffer')
 const { getWebGLDrawBuffers } = require('./extensions/webgl-draw-buffers')
+const { getEXTBlendMinMax } = require('./extensions/ext-blend-minmax')
 const {
   bindPublics,
   checkObject,
@@ -57,7 +58,8 @@ const availableExtensions = {
   oes_standard_derivatives: getOESStandardDerivatives,
   stackgl_destroy_context: getSTACKGLDestroyContext,
   stackgl_resize_drawingbuffer: getSTACKGLResizeDrawingBuffer,
-  webgl_draw_buffers: getWebGLDrawBuffers
+  webgl_draw_buffers: getWebGLDrawBuffers,
+  ext_blend_minmax: getEXTBlendMinMax
 }
 
 const privateMethods = [
@@ -769,7 +771,10 @@ class WebGLRenderingContext extends NativeWebGLRenderingContext {
   _validBlendMode (mode) {
     return mode === gl.FUNC_ADD ||
       mode === gl.FUNC_SUBTRACT ||
-      mode === gl.FUNC_REVERSE_SUBTRACT
+      mode === gl.FUNC_REVERSE_SUBTRACT ||
+      (this._extensions.ext_blend_minmax && (
+        mode === this._extensions.ext_blend_minmax.MIN_EXT ||
+        mode === this._extensions.ext_blend_minmax.MAX_EXT))
   }
 
   _validCubeTarget (target) {
@@ -1211,6 +1216,10 @@ class WebGLRenderingContext extends NativeWebGLRenderingContext {
       exts.push('WEBGL_draw_buffers')
     }
 
+    if (supportedExts.indexOf('EXT_blend_minmax') >= 0) {
+      exts.push('EXT_blend_minmax')
+    }
+
     return exts
   }