# glPolygonOffset

## Name

glPolygonOffset — set the scale and units 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_FILL 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 $factor × DZ + r × units$, 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.

## Associated Gets

glIsEnabled with argument GL_POLYGON_OFFSET_FILL.

glGet with argument GL_POLYGON_OFFSET_FACTOR or GL_POLYGON_OFFSET_UNITS.