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 blendFuncSeparateiOES() for setting RGB and alpha components separately and blendFunc() for the WebGL 1 version of this method.

Syntax

blendFunciOES(buf, src, dst)

Parameters

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

Return value

None (undefined).

Exceptions

• 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 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.

Examples

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 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);

Specifications

Browser compatibility

See also

• blendFuncSeparateiOES()
• blendFunc()