NAME

glPolygonOffset - set the scale and units used to calculate depth values

C SPECIFICATION

void ggllPPoollyyggoonnOOffffsseett( GLfloat _f_a_c_t_o_r,
                      GLfloat _u_n_i_t_s )

delim $$

PARAMETERS

_f_a_c_t_o_r
Specifies a scale factor that is used to create a variable depth offset for each polygon. The initial value is 0.
_u_n_i_t_s
Is multiplied by an implementation-specific value to create a constant depth offset. The initial value is 0.

DESCRIPTION

When GGLL__PPOOLLYYGGOONN__OOFFFFSSEETT__FFIILLLL, GGLL__PPOOLLYYGGOONN__OOFFFFSSEETT__LLIINNEE, or GGLL__PPOOLLYYGGOONN__OOFFFFSSEETT__PPOOIINNTT is enabled, each fragment's _d_e_p_t_h value will be offset after it is interpolated from the _d_e_p_t_h 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.

ggllPPoollyyggoonnOOffffsseett is useful for rendering hidden-line images, for applying decals to surfaces, and for rendering solids with highlighted edges.

NOTES

ggllPPoollyyggoonnOOffffsseett is available only if the GL version is 1.1 or greater.

ggllPPoollyyggoonnOOffffsseett has no effect on depth coordinates placed in the feedback buffer.

ggllPPoollyyggoonnOOffffsseett has no effect on selection.

ERRORS

GGLL__IINNVVAALLIIDD__OOPPEERRAATTIIOONN is generated if ggllPPoollyyggoonnOOffffsseett is executed between the execution of ggllBBeeggiinn and the corresponding execution of ggllEEnndd.

ASSOCIATED GETS

ggllIIssEEnnaabblleedd with argument GGLL__PPOOLLYYGGOONN__OOFFFFSSEETT__FFIILLLL, GGLL__PPOOLLYYGGOONN__OOFFFFSSEETT__LLIINNEE, or GGLL__PPOOLLYYGGOONN__OOFFFFSSEETT__PPOOIINNTT.

ggllGGeett with argument GGLL__PPOOLLYYGGOONN__OOFFFFSSEETT__FFAACCTTOORR or GGLL__PPOOLLYYGGOONN__OOFFFFSSEETT__UUNNIITTSS.

SEE ALSO

ggllDDeepptthhFFuunncc((33GG)), ggllEEnnaabbllee((33GG)), ggllGGeett((33GG)), ggllIIssEEnnaabblleedd((33GG))