- set the scale and units used to calculate depth values
C SPECIFICATION
PARAMETERS
_param1 Specifies a scale factor that is used to create a
variable depth offset for each polygon. The ini-
tial value is 0.
_param2 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 _eqnparam1*DZ+r*_eqnparam2, 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.
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 corre-
sponding execution of glEnd.
SEE ALSO
glDepthFunc, glEnable, glGet, glIsEnabled
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