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glPolygonOffset
Chapter 14
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glPolygonOffset
glPolygonOffset: set the scale and bias used to calculate depth values.
C Specification
void glPolygonOffset(
GLfloat factor,
GLfloat units)
Parameters
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 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 ×∆z+r× units, where z 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.
Notes
glPolygonOffset is available only if the GL version is 1.1 or greater.
glPolygonOffset has no effect on depth coordinates placed in the feedback buffer.
glPolygonOffset has no effect on selection.
Errors
• GL_INVALID_OPERATION is generated if glPolygonOffset is executed between the
execution of glBegin and the corresponding execution of glEnd.
Associated Gets
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.
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