glPolygonOffset

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 $\mathit{factor}\mathit{DZ}+\mathit{r}\mathit{units}$ , where $\mathit{DZ}$ is a measurement of the change in depth relative to the screen area of the polygon, and $\mathit{r}$ 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.

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 .

glDepthFunc , glEnable , glGet , glIsEnabled

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