gl_CullDistance - OpenGL 4 Reference Pages

## Name

gl_CullDistance — provides a mechanism for controlling user culling

## Declaration

`gl_CullDistance` is a member of the `gl_PerVertex` named block:

        out gl_PerVertex {
            vec4 gl_Position;
            float gl_PointSize;
            float gl_ClipDistance[];
            float gl_CullDistance[];
        };

In fragment shaders, it is intrinsically declared as: `in float gl_CullDistance[] ;`

## Description

The `gl_CullDistance` variable provides a mechanism for controlling user culling. The element `gl_CullDistance`[i] specifies a cull distance for each plane i. A distance of 0.0 means that the vertex is on the plane, a positive distance means that the vertex is insider the cull volume, and a negative distance means that the point is outside the cull volume. Primitives whose vertices all have a negative clip distance for plane i will be discarded.

The `gl_CullDistance` array is predeclared as unsized and must be sized by the shader either by redeclaring it with an size or by indexing it only with integral constant expressions. The size determines the number and set of enabled cull distances and can be at most `gl_MaxCullDistances`. The number of varying components consumed by `gl_CullDistance` will match the size of the array. Shaders writing `gl_CullDistance` must write all enabled distances, or culling results are undefined.

As an output variable, `gl_CullDistance` provides the place for the shader to write these distances. As an input in all but the fragment language, it reads the values written in the previous shader stage. In the fragment language, the `gl_CullDistance` array contains linearly interpolated values for the vertex values written by a shader to the `gl_CullDistance` vertex output variable.

It is a compile-time or link-time error for the set of shaders forming a program to have the sum of the sizes of the `gl_ClipDistance` and `gl_CullDistance` arrays to be larger than `gl_MaxCombinedClipAndCullDistances`.

## Version Support

| OpenGL Shading Language Version
--- | ---
Variable Name | 1.10 | 1.20 | 1.30 | 1.40 | 1.50 | 3.30 | 4.00 | 4.10 | 4.20 | 4.30 | 4.40 | 4.50
gl_CullDistance | - | - | - | - | - | - | - | - | - | - | - | ✔

## See Also

gl_ClipDistance, gl_PointSize

## Copyright

Copyright © 2014 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.