The blendFuncSeparateiOES() method of the OES_draw_buffers_indexed WebGL extension defines which function is used when blending pixels for RGB and alpha components separately for a particular draw buffer.

See OES_draw_buffers_indexed.blendFunciOES() for setting RGB and alpha together and WebGLRenderingContext.blendFuncSeparate() for the WebGL 1 version of this method.

buf

An integer i specifying the draw buffer associated with the constant gl.DRAW_BUFFERi, see WebGL draw buffer constants.

srcRGB

A GLenum specifying a multiplier for the red, green and blue (RGB) source blending factors. Accepts the same enums as the srcRGB parameter in WebGLRenderingContext.blendFuncSeparate().

dstRGB

A GLenum specifying a multiplier for the red, green and blue (RGB) destination blending factors. Accepts the same enums as the dstRGB parameter in WebGLRenderingContext.blendFuncSeparate().

srcAlpha

A GLenum specifying a multiplier for the alpha source blending factor. Accepts the same enums as the srcAlpha parameter in WebGLRenderingContext.blendFuncSeparate().

dstAlpha

A GLenum specifying a multiplier for the alpha destination blending factor. Accepts the same enums as the srcAlpha parameter in WebGLRenderingContext.blendFuncSeparate().

None (undefined).

• If buf is not a valid value, a gl.INVALID_VALUE error is thrown.
• If srcRGB, dstRGB, srcAlpha or dstAlpha are not one of the possible values, a gl.INVALID_ENUM error is thrown.
• The same blending limitations as for WebGLRenderingContext.blendFuncSeparate() apply: If a constant color and a constant alpha value are used together as source and destination factors, a gl.INVALID_ENUM error is thrown.

The following sets the blend functions for the draw buffers gl.DRAW_BUFFER0 (call where buf is 0) and gl.DRAW_BUFFER1 (call where buf is 1).

const ext = gl.getExtension("OES_draw_buffers_indexed");

ext.blendFuncSeparateiOES(0, gl.ONE, gl.ONE, gl.ZERO, gl.ZERO);
ext.blendFuncSeparateiOES(
  1,
  gl.SRC_ALPHA,
  gl.ONE_MINUS_SRC_ALPHA,
  gl.ZERO,
  gl.ZERO,
);

To get the blend functions for the gl.DRAW_BUFFER0 and gl.DRAW_BUFFER1 draw buffers, query the BLEND_SRC_RGB, BLEND_SRC_ALPHA, BLEND_DST_RGB, and BLEND_DST_ALPHA constants using WebGL2RenderingContext.getIndexedParameter():

// For gl.DRAW_BUFFER0
gl.getIndexedParameter(gl.BLEND_SRC_RGB, 0);
gl.getIndexedParameter(gl.BLEND_SRC_ALPHA, 0);
gl.getIndexedParameter(gl.BLEND_DST_RGB, 0);
gl.getIndexedParameter(gl.BLEND_DST_ALPHA, 0);

// For gl.DRAW_BUFFER0
gl.getIndexedParameter(gl.BLEND_SRC_RGB, 1);
gl.getIndexedParameter(gl.BLEND_SRC_ALPHA, 1);
gl.getIndexedParameter(gl.BLEND_DST_RGB, 1);
gl.getIndexedParameter(gl.BLEND_DST_ALPHA, 1);

• OES_draw_buffers_indexed.blendFunciOES()
• WebGLRenderingContext.blendFuncSeparate()