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The WebGLRenderingContext.blendFuncSeparate() method of the WebGL API defines which function is used for blending pixel arithmetic for RGB and alpha components separately.
Syntax
void gl.blendFuncSeparate(srcRGB, dstRGB, srcAlpha, dstAlpha);
Parameters
srcRGB- A
GLenumspecifying a multiplier for the red, green and blue (RBG) source blending factors. The default value isgl.ONE. For possible values, see below. dstRBG- A
GLenumspecifying a multiplier for the red, green and blue (RBG) destination blending factors. The default value isgl.ZERO. For possible values, see below. srcAlpha- A
GLenumspecifying a multiplier for the alpha source blending factor. The default value isgl.ONE. For possible values, see below. dstAlpha- A
GLenumspecifying a multiplier for the alpha destination blending factor. The default value isgl.ZERO. For possible values, see below.
Errors thrown
If srcRGB, dstRGB, srcAlpha, or dstAlpha is not one of the listed possible values, a gl.INVALID_ENUM error is thrown.
Return value
None.
Constants
The following constants can be used for srcRGB, dstRGB, srcAlpha, and dstAlpha
The formulas for the blending factors can be described like this (all RGBA values are between 0 and 1):
- color(RGB) = (sourceColor * srcRGB) + (destinationColor * dstRGB)
- color(A) = (sourceAlpha * srcAlpha) + (destinationAlpha * dstAlpha)
| Constant | RGB factor | Alpha factor | Description |
|---|---|---|---|
gl.ZERO |
0,0,0 | 0 | Multiplies all colors by 0. |
gl.ONE |
1,1,1,1 | 1 | Multiplies all colors by 1. |
gl.SRC_COLOR |
RS, GS, BS | AS | Multiplies all colors by the source colors. |
gl.ONE_MINUS_SRC_COLOR |
1-RS, 1-GS, 1-BS | 1-AS | Multiplies all colors by 1 minus each source color. |
gl.DST_COLOR |
RD, GD, BD | AD | Multiplies all colors by the destination color. |
gl.ONE_MINUS_DST_COLOR |
1-RD, 1-GD, 1-BD | 1-AD | Multiplies all colors by 1 minus each destination color. |
gl.SRC_ALPHA |
AS, AS, AS | AS | Multiplies all colors by the source alpha color. |
gl.ONE_MINUS_SRC_ALPHA |
1-AS, 1-AS, 1-AS | 1-AS | Multiplies all colors by 1 minus the source alpha color. |
gl.DST_ALPHA |
AD, AD, AD | AD | Multiplies all colors by the destination alpha color. |
gl.ONE_MINUS_DST_ALPHA |
1-AD, 1-AD, 1-AD | 1-AD | Multiplies all colors by 1 minus the destination alpha color. |
gl.SRC_ALPHA_SATURATE |
min(AS, 1 - AD), min(AS, 1 - AD), min(AS, 1 - AD) |
1 | Multiplies the RGB colors by the smaller of either the source alpha color or the value of 1 minus the destination alpha color. The alpha value is multiplied by 1. |
Examples
To use the blend function, you first have to activate blending with WebGLRenderingContext.enable() with the argument gl.BLEND.
gl.enable(gl.BLEND); gl.blendFuncSeparate(gl.SRC_COLOR, gl.DST_COLOR, gl.ONE, gl.ZERO);
To get the current blend function, query the BLEND_SRC_RGB, BLEND_SRC_ALPHA, BLEND_DST_RGB, and BLEND_DST_ALPHA constants which return one of the blend function constants.
gl.enable(gl.BLEND); gl.blendFuncSeparate(gl.SRC_COLOR, gl.DST_COLOR, gl.ONE, gl.ZERO); gl.getParameter(gl.BLEND_SRC_RGB) == gl.SRC_COLOR; // true
Specifications
| Specification | Status | Comment |
|---|---|---|
| WebGL 1.0 The definition of 'blendFunc' in that specification. |
Recommendation | Initial definition. In WebGL, the following constants can't be used, but are defined in OpenGL: CONSTANT_COLOR, ONE_MINUS_CONSTANT_COLOR, CONSTANT_ALPHA, ONE_MINUS_CONSTANT_ALPHA. |
| OpenGL ES 2.0 The definition of 'glBlendFunc' in that specification. |
Standard | Man page of the OpenGL API. |
Browser compatibility
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | 9 | 4.0 (2.0) | 11 | 12 | 5.1 |
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|
| Basic support | ? | 25 | (Yes) | ? | 12 | 8.1 |