glClipControl

From OpenGL Reference
Jump to navigation Jump to search

Control clip coordinate to window coordinate behavior.

C Specification[edit]

void glClipControl( GLenum origin, GLenum depth );


Parameters[edit]

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[edit]

 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[edit]

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 theGL_ARB_clip_controlextension specification in the OpenGL Registry at URL http://www.opengl.org/registry/.


Errors[edit]

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[edit]

 glClipControl  4.5+

See Also[edit]

 gl_ClipDistance , gl_CullDistance , gl_FrontFacing , glDepthRange .


Copyright[edit]

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/.