OES_draw_buffers_indexed: blendEquationSeparateiOES() method

Baseline 2022

Newly available

Since December 2022, this feature works across the latest devices and browser versions. This feature might not work in older devices or browsers.

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

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


blendEquationSeparateiOES(buf, modeRGB, modeAlpha)



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 RGB color components are combined. Accepts the same enums as the modeRGB parameter in WebGLRenderingContext.blendEquationSeparate().


A GLenum specifying how source and destination alpha color components are combined. Accepts the same enums as the modeAlpha parameter in WebGLRenderingContext.blendEquationSeparate().

Return value

None (undefined).


  • If buf is not a valid value, a gl.INVALID_VALUE error is thrown.
  • If modeRGB or modeAlpha are not set to one of the possible values, a gl.INVALID_ENUM error is thrown.


Setting and getting blend equations

The following sets the blend equations 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.blendEquationSeparateiOES(0, gl.FUNC_ADD, gl.FUNC_SUBTRACT);
ext.blendEquationSeparateiOES(1, gl.FUNC_ADD, gl.FUNC_SUBTRACT);

To get the blend equations for gl.DRAW_BUFFER0 and gl.DRAW_BUFFER1, 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_BUFFER1
gl.getIndexedParameter(gl.BLEND_EQUATION_RGB, 1);
gl.getIndexedParameter(gl.BLEND_EQUATION_ALPHA, 1);


WebGL OES_draw_buffers_indexed Extension Specification

Browser compatibility

BCD tables only load in the browser

See also