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 , where 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.
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.
glIsEnabled with argument
glGet with argument
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