glPolygonOffset — set the scale and units used to calculate depth values
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.
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
is a measurement of the change in depth relative to the screen
area of the polygon, and
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.
glIsEnabled with argument
glGet with argument
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