WebGLRenderingContext.blendFunc()

The WebGLRenderingContext.blendFunc() method of the WebGL API defines which function is used for blending pixel arithmetic.

Syntax

void gl.blendFunc(sfactor, dfactor);

Parameters

sfactor
A GLenum specifying a multiplier for the source blending factors. The default value is gl.ONE. For possible values, see below.
dfactor
A GLenum specifying a multiplier for the destination blending factors. The default value is gl.ZERO. For possible values, see below.

Return value

None.

Exceptions

  • If sfactor or dfactor is not one of the listed possible values, a gl.INVALID_ENUM error is thrown.
  • If a constant color and a constant alpha value are used together as source and destination factors, a gl.INVALID_ENUM error is thrown.

Constants

The following constants can be used for sfactor and dfactor.

The formula for the blending color can be described like this: color(RGBA) = (sourceColor * sfactor) + (destinationColor * dfactor). The RBGA values are between 0 and 1.

Constant Factor Description
gl.ZERO 0,0,0,0 Multiplies all colors by 0.
gl.ONE 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 value.
gl.ONE_MINUS_SRC_ALPHA 1-AS, 1-AS, 1-AS, 1-AS Multiplies all colors by 1 minus the source alpha value.
gl.DST_ALPHA AD, AD, AD, AD Multiplies all colors by the destination alpha value.
gl.ONE_MINUS_DST_ALPHA 1-AD, 1-AD, 1-AD, 1-AD Multiplies all colors by 1 minus the destination alpha value.
gl.CONSTANT_COLOR RC, GC, BC, AC Multiplies all colors by a constant color.
gl.ONE_MINUS_CONSTANT_COLOR 1-RC, 1-GC, 1-BC, 1-AC Multiplies all colors by 1 minus a constant color.
gl.CONSTANT_ALPHA AC, AC, AC, AC Multiplies all colors by a constant alpha value.
gl.ONE_MINUS_CONSTANT_ALPHA 1-AC, 1-AC, 1-AC, 1-AC Multiplies all colors by 1 minus a constant alpha value.
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 value or the value of 1 minus the destination alpha value. 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.blendFunc(gl.SRC_COLOR, gl.DST_COLOR);

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.blendFunc(gl.SRC_COLOR, gl.DST_COLOR);
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, constant color and constant alpha cannot be used together as source and destination factors in the blend function. See section 6.13. of the specification.
OpenGL ES 2.0
The definition of 'glBlendFunc' in that specification.		 Standard Man page of the OpenGL API.

Browser compatibility

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See also