GlPolygonOffset
_glPolygonOffset: set the scale and units used to calculate depth values
Syntax
SUB _glPolygonOffset (BYVAL factor AS SINGLE, BYVAL units AS SINGLE) void _glPolygonOffset(GLfloat factor, GLfloat units);
- factor
- Specifies a scale factor that is used to create a variable depth offset for each polygon. The initial value is 0.
- units
- Is multiplied by an implementation-specific value to create a constant depth offset. The initial value is 0.
Description
When _GL_POLYGON_OFFSET_FILL, _GL_POLYGON_OFFSET_LINE, or _GL_POLYGON_OFFSET_POINT is enabled, each fragment's depth value will be offset after it is interpolated from the depth values of the appropriate vertices. The value of the offset is factor * DZ + r * units, where DZ is a measurement of the change in depth relative to the screen area of the polygon, and r is the smallest value that is guaranteed to produce a resolvable offset for a given implementation. The offset is added before the depth test is performed and before the value is written into the depth buffer.
_glPolygonOffset is useful for rendering hidden-line images, for applying decals to surfaces, and for rendering solids with highlighted edges.
Use With:
_glIsEnabled with argument _GL_POLYGON_OFFSET_FILL, _GL_POLYGON_OFFSET_LINE, or _GL_POLYGON_OFFSET_POINT.
_glGet with argument _GL_POLYGON_OFFSET_FACTOR or _GL_POLYGON_OFFSET_UNITS.
See also
SUB _GL _glDepthFunc, _glEnable
Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.
