_glPolygonOffset: set the scale and units used to calculate depth values
SUB _glPolygonOffset (BYVAL factor AS SINGLE, BYVAL units AS SINGLE) void _glPolygonOffset(GLfloat factor, GLfloat units);
- Specifies a scale factor that is used to create a variable depth offset for each polygon. The initial value is 0.
- Is multiplied by an implementation-specific value to create a constant depth offset. The initial value is 0.
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.
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