The blendFunciOES() method of the OES_draw_buffers_indexed WebGL extension defines which function is used when blending pixels for a particular draw buffer.

See OES_draw_buffers_indexed.blendFuncSeparateiOES() for setting RGB and alpha components separately and WebGLRenderingContext.blendFunc() 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.

src

A GLenum specifying a multiplier for the source blending factors. Accepts the same enums as the sfactor parameter in WebGLRenderingContext.blendFunc().

dst

A GLenum specifying a multiplier for the destination blending factors. Accepts the same enums as the dfactor parameter in WebGLRenderingContext.blendFunc().

None (undefined).

• If buf is not a valid value, a gl.INVALID_VALUE error is thrown.
• If src or dst are not one of the possible values, a gl.INVALID_ENUM error is thrown.
• The same blending limitations as for WebGLRenderingContext.blendFunc() 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.

You can set the blend functions for the gl.DRAW_BUFFER0 and gl.DRAW_BUFFER1 draw buffers like this:

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

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

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.blendFuncSeparateiOES()
• WebGLRenderingContext.blendFunc()