WebGL WEBGL_blend_func_extended Extension Specification

Name

WEBGL_blend_func_extended

Contact

WebGL working group (public_webgl 'at' khronos.org)

Contributors

Members of the WebGL working group

Version

Last modified date: January 11, 2024
Revision: 2

Number

WebGL extension #58

Dependencies

Written against the WebGL API 1.0 specification.

Overview

This extension exposes the EXT_blend_func_extended functionality to WebGL.

The following WebGL-specific behavioral changes apply:

• Although the extension name is WEBGL_blend_func_extended, the extension must be enabled with the #extension GL_EXT_blend_func_extended directive to use its functionality in shaders. Likewise the shading language preprocessor #define GL_EXT_blend_func_extended, will be defined to 1 if the extension is supported.
• None of the new API functions are supported.
• Automatic location assignment of fragment outputs is not supported.

• INVALID_OPERATION is generated by attempting to draw when any of the SRC1 blend factors are used for an active draw buffer, which has blending enabled, and the fragment shader does not

  • ESSL 1.00: statically write to gl_SecondaryFragColorEXT or to the appropriate element of the gl_SecondaryFragDataEXT[] array.
  • ESSL 3.00: statically bind a compatible fragment output as the secondary blending source for the corresponding draw buffer.

Consult the above extension for documentation, issues and new functions and enumerants.

When this extension is enabled:

• When a fragment shader enables, requires, or warns GL_EXT_blend_func_extended with an #extension directive:
  • int gl_MaxDualSourceDrawBuffersEXT is a built-in constant.
  • ESSL 1.00: gl_SecondaryFragColorEXT and gl_SecondaryFragDataEXT[] are built-in outputs.
  • ESSL 3.00: An index layout qualifier may be used to bind fragment shader outputs as secondary blend sources.
• The GLSL macro GL_EXT_blend_func_extended is defined as 1.

IDL

[Exposed=(Window,Worker), LegacyNoInterfaceObject]
interface WEBGL_blend_func_extended {
    const GLenum SRC1_COLOR_WEBGL                   = 0x88F9;
    const GLenum SRC1_ALPHA_WEBGL                   = 0x8589;
    const GLenum ONE_MINUS_SRC1_COLOR_WEBGL         = 0x88FA;
    const GLenum ONE_MINUS_SRC1_ALPHA_WEBGL         = 0x88FB;
    const GLenum MAX_DUAL_SOURCE_DRAW_BUFFERS_WEBGL = 0x88FC;
};
  

New Tokens

undefined blendFunc(GLenum src, GLenum dst)

New enums SRC1_COLOR_WEBGL, SRC1_ALPHA_WEBGL, ONE_MINUS_SRC1_COLOR_WEBGL, and ONE_MINUS_SRC1_ALPHA_WEBGL are accepted as the src and dst parameters.

WebGL 1.0: An existing enum SRC_ALPHA_SATURATE is accepted as the dst parameter.

undefined blendFuncSeparate(GLenum srcRGB, GLenum dstRGB, GLenum srcAlpha, GLenum dstAlpha)

New enums SRC1_COLOR_WEBGL, SRC1_ALPHA_WEBGL, ONE_MINUS_SRC1_COLOR_WEBGL, and ONE_MINUS_SRC1_ALPHA_WEBGL are accepted as the srcRGB, dstRGB, srcAlpha, and dstAlpha parameters.

WebGL 1.0: An existing enum SRC_ALPHA_SATURATE is accepted as the dstRGB and dstAlpha parameters.

undefined blendFunciOES(GLuint buf, GLenum src, GLenum dst)

When OES_draw_buffers_indexed is enabled, new enums SRC1_COLOR_WEBGL, SRC1_ALPHA_WEBGL, ONE_MINUS_SRC1_COLOR_WEBGL, and ONE_MINUS_SRC1_ALPHA_WEBGL are accepted as the src and dst parameters.

undefined blendFuncSeparateiOES(GLuint buf, GLenum srcRGB, GLenum dstRGB, GLenum srcAlpha, GLenum dstAlpha)

When OES_draw_buffers_indexed is enabled, new enums SRC1_COLOR_WEBGL, SRC1_ALPHA_WEBGL, ONE_MINUS_SRC1_COLOR_WEBGL, and ONE_MINUS_SRC1_ALPHA_WEBGL are accepted as the srcRGB, dstRGB, srcAlpha, and dstAlpha parameters.

any getParameter(GLenum pname)

New MAX_DUAL_SOURCE_DRAW_BUFFERS_WEBGL enum is accepted as the pname parameter.

The return type of this method depends on the parameter queried:

pname	returned type
MAX_DUAL_SOURCE_DRAW_BUFFERS_WEBGL	GLint

Revision History

Revision 1, 2023/06/01

• Initial Draft.

Revision 2, 2024/01/11

• Changed prefix to WEBGL and promoted to Community Approved.