glClipControl - OpenGL 4 Reference Pages

## Name

glClipControl — control clip coordinate to window coordinate behavior

## C Specification

`void glClipControl(` | GLenum origin,
| GLenum depth`)`;

## Parameters

`origin`

  Specifies the clip control origin. Must be one of `GL_LOWER_LEFT` or `GL_UPPER_LEFT`.

`depth`

  Specifies the clip control depth mode. Must be one of `GL_NEGATIVE_ONE_TO_ONE` or `GL_ZERO_TO_ONE`.

## Description

`glClipControl` controls the clipping volume behavior and the clip coordinate to window coordinate transformation behavior.

The view volume is defined by $$z_{min} \leq z_c \leq w_c$$ where $z_{min} = -w_c$ when `depth` is `GL_NEGATIVE_ONE_TO_ONE`, and $z_{min} = 0$ when `depth` is `GL_ZERO_TO_ONE`.

The normalized device coordinate $y_d$ is given by $$y_d = { { f \times y_c } \over w_c }$$ where $f = 1$ when `origin` is `GL_LOWER_LEFT`, and $f = -1$ when `origin` is `GL_UPPER_LEFT`.

The window coordinate $z_w$ is given by $$z_w = s \times z_d + b$$ where $s = { { f - n } \over 2 }$ and $b = { {n + f} \over 2 }$ when `depth` is `GL_NEGATIVE_ONE_TO_ONE`, and $s = f - n$ and $b = n$ when `depth` is `GL_ZERO_TO_ONE`. $n$ and $f$ are the near and far depth range values set with glDepthRange.

Finally, the polygon area computation defined by gl_FrontFacing to determine if a polygon is front- or back-facing has its sign negated when `origin` is `GL_UPPER_LEFT`.

## Notes

The default GL clip volume definition is for a `origin` of `GL_LOWER_LEFT` and a `depth` of `GL_NEGATIVE_ONE_TO_ONE`.

An `origin` of `GL_UPPER_LEFT` and a `depth` of `GL_ZERO_TO_ONE` corresponds to Direct3D's clip volume definition.

An `origin` of `GL_UPPER_LEFT` and a `depth` of `GL_NEGATIVE_ONE_TO_ONE` corresponds to the upper-left origin of the window coordinate system of Microsoft Windows and the X Window System.

There is extensive discussion of the uses and further consequences of the different clip volume settings in the `GL_ARB_clip_control` extension specification in the OpenGL Registry at URL http://www.opengl.org/registry/.

## Errors

An `GL_INVALID_ENUM` error is generated if `origin` is not `GL_LOWER_LEFT` or `GL_UPPER_LEFT`.

An `GL_INVALID_ENUM` error is generated if `depth` is not `GL_NEGATIVE_ONE_TO_ONE` or `GL_ZERO_TO_ONE`.

## Version Support

| OpenGL Version
--- | ---
Function / Feature Name | 2.0 | 2.1 | 3.0 | 3.1 | 3.2 | 3.3 | 4.0 | 4.1 | 4.2 | 4.3 | 4.4 | 4.5
`glClipControl` | - | - | - | - | - | - | - | - | - | - | - | ✔

## See Also

gl_ClipDistance, gl_CullDistance, gl_FrontFacing, glDepthRange.

## 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/.