HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 342

P glPolygonOffset glPolygonOffset glPolygonOffset: set the scale and bias used to calculate depth values. C Specification void glPolygonOffset( GLfloat factor, GLfloat units) Parameters factor units 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. Description When GL_POLYGON_OFFSET 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 × ∆z + r × units, where z 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 corresponding execution of glEnd. Associated Gets 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. 342 Chapter 14