The blendEquationiOES() method of the OES_draw_buffers_indexed WebGL extension sets both the RGB blend and alpha blend equations for a particular draw buffer.

See OES_draw_buffers_indexed.blendEquationSeparateiOES() for setting RGB and alpha separately and WebGLRenderingContext.blendEquation() for the WebGL 1 version of this method.


blendEquationiOES(buf, mode)



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


A GLenum specifying how source and destination colors are combined. Accepts the same enums as the mode parameter in WebGLRenderingContext.blendEquation().

Return value

None (undefined).


  • If buf is not a valid value, a gl.INVALID_VALUE error is thrown.
  • If mode is not one of the possible values, a gl.INVALID_ENUM error is thrown.


Setting and getting blend equations

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

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

ext.blendEquationiOES(0, gl.FUNC_ADD);
ext.blendEquationiOES(1, gl.FUNC_SUBTRACT);

To get the blend equations for the gl.DRAW_BUFFER0 and gl.DRAW_BUFFER1 draw buffers, query the BLEND_EQUATION_RGB and BLEND_EQUATION_ALPHA constants using WebGL2RenderingContext.getIndexedParameter():

// For gl.DRAW_BUFFER0
gl.getIndexedParameter(gl.BLEND_EQUATION_RGB, 0);
gl.getIndexedParameter(gl.BLEND_EQUATION_ALPHA, 0);

// For gl.DRAW_BUFFER0
gl.getIndexedParameter(gl.BLEND_EQUATION_RGB, 1);
gl.getIndexedParameter(gl.BLEND_EQUATION_ALPHA, 1);


WebGL OES_draw_buffers_indexed Extension Specification

Browser compatibility

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See also