WebGL EXT_clip_cull_distance Extension Draft Specification

Name

EXT_clip_cull_distance

Contact

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

Contributors

Members of the WebGL working group

Kevin Rogovin (kevinrogovin[at]invisionapp.com

Version

Last modified date: July 01, 2020
Revision: 3

Number

WebGL extension #43

Dependencies

Written against the WebGL API 2.0 specification.

Overview

This extension exposes the EXT_clip_cull_distance functionality to WebGL.

The following WebGL-specific behavioral changes apply:

• WebGL implementations can return 0 for the maximum number cull planes (MAX_CULL_DISTANCES_EXT) supported.

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

When this extension is enabled:

• Adds support for hardware clip planes and cull distances to OpenGL ES.
• When a vertex or fragment shader enables, requires, or warns GL_EXT_clip_cull_distance with an #extension directive:
  • highp float gl_ClipDistance[] is a built-in input.
  • highp float gl_CullDistance[] is a built-in input.
  • highp float gl_ClipDistance[] is a built-in output.
  • highp float gl_CullDistance[] is a built-in output.
• The GLSL macro GL_EXT_clip_cull_distance is defined as 1.

IDL

    [LegacyNoInterfaceObject]
    interface EXT_clip_cull_distance {
      const GLenum MAX_CLIP_DISTANCES_EXT                       = 0x0D32;
      const GLenum MAX_CULL_DISTANCES_EXT                       = 0x82F9;
      const GLenum MAX_COMBINED_CLIP_AND_CULL_DISTANCES_EXT     = 0x82FA;

      const GLenum CLIP_DISTANCE0_EXT                           = 0x3000;
      const GLenum CLIP_DISTANCE1_EXT                           = 0x3001;
      const GLenum CLIP_DISTANCE2_EXT                           = 0x3002;
      const GLenum CLIP_DISTANCE3_EXT                           = 0x3003;
      const GLenum CLIP_DISTANCE4_EXT                           = 0x3004;
      const GLenum CLIP_DISTANCE5_EXT                           = 0x3005;
      const GLenum CLIP_DISTANCE6_EXT                           = 0x3006;
      const GLenum CLIP_DISTANCE7_EXT                           = 0x3007;
    };
  

Sample Code

    #extension GL_EXT_clip_cull_distance : enable

    // Vertex shader
    out highp float gl_ClipDistance[2];
    out highp float gl_CullDistance[2];

    void main(){
        // Compute the clip and cull distances for this vertex
        gl_ClipDistance[0] = ...;
        gl_CullDistance[0] = ...;
        gl_ClipDistance[1] = ...;
        gl_CullDistance[1] = ...;
    }
    

Revision History

Revision 1, 2016/08/22

• Initial revision.

Revision 2, 2019/09/25

• Promoted to Draft.

Revision 3, 2020/07/01

• Added addendum that allows for the number of cull planes to be 0.