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Showing content from http://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/blendFunc below:

WebGLRenderingContext: blendFunc() method - Web APIs

WebGLRenderingContext: blendFunc() method

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

Syntax

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 (undefined).

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 RGBA values are between 0 and 1.

In the following table, R_S, G_S, B_S, A_S represent respectively the red, green, blue and alpha component of the source, while R_D, G_D, B_D, A_D represent respectively the red, green, blue and alpha component of the destination. Similarly, R_C, G_C, B_C, A_C represent respectively the red, green, blue and alpha component of a constant color. They are all values between 0 and 1, included.

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 R_S, G_S, B_S, A_S Multiplies all colors by the source colors. gl.ONE_MINUS_SRC_COLOR 1-R_S, 1-G_S, 1-B_S, 1-A_S Multiplies all colors by 1 minus each source color. gl.DST_COLOR R_D, G_D, B_D, A_D Multiplies all colors by the destination color. gl.ONE_MINUS_DST_COLOR 1-R_D, 1-G_D, 1-B_D, 1-A_D Multiplies all colors by 1 minus each destination color. gl.SRC_ALPHA A_S, A_S, A_S, A_S Multiplies all colors by the source alpha value. gl.ONE_MINUS_SRC_ALPHA 1-A_S, 1-A_S, 1-A_S, 1-A_S Multiplies all colors by 1 minus the source alpha value. gl.DST_ALPHA A_D, A_D, A_D, A_D Multiplies all colors by the destination alpha value. gl.ONE_MINUS_DST_ALPHA 1-A_D, 1-A_D, 1-A_D, 1-A_D Multiplies all colors by 1 minus the destination alpha value. gl.CONSTANT_COLOR R_C, G_C, B_C, A_C Multiplies all colors by a constant color. gl.ONE_MINUS_CONSTANT_COLOR 1-R_C, 1-G_C, 1-B_C, 1-A_C Multiplies all colors by 1 minus a constant color. gl.CONSTANT_ALPHA A_C, A_C, A_C, A_C Multiplies all colors by a constant alpha value. gl.ONE_MINUS_CONSTANT_ALPHA 1-A_C, 1-A_C, 1-A_C, 1-A_C Multiplies all colors by 1 minus a constant alpha value. gl.SRC_ALPHA_SATURATE min(A_S, 1 - A_D), min(A_S, 1 - A_D), min(A_S, 1 - A_D), 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 Browser compatibility See also

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