/Web APIs

OES_draw_buffers_indexed: blendFunciOES() method

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.


blendFunciOES(buf, src, dst)



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


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


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

Return value

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.


Setting and getting blend functions

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);


Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
blendFunciOES 100 100 108 No 86 16 100 100 108 69 16 19.0

See also

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