glClipControl - control clip coordinate to window coordinate behavior
void glClipControl(GLenum origin, GLenum depth); |
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.
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.
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/.
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.
gl_ClipDistance(), gl_CullDistance(), gl_FrontFacing(), glDepthRange().
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/.
Copyright © 2014 Khronos Group