pfShadeModel(3pf) OpenGL Performer 3.2.2 libpr C++ Reference Pages
NAME
pfShadeModel, pfGetShadeModel - Set and get the shading model
FUNCTION SPECIFICATION
#include <Performer/pr.h>
void pfShadeModel(int model);
int pfGetShadeModel(void);
PARAMETERS
model is a symbolic constant and is one of:
PFSM_FLAT Use flat shading,
PFSM_GOURAUD Use Gouraud shading.
DESCRIPTION
pfShadeModel sets the shading model to model. When flat shading is
enabled, the last vertex in a geometric primitive defines the color of
the entire geometric primitive. When Gouraud shading, vertex colors are
interpolated across the primitive.
The following example shows how data equivalent to OpenGL immediate mode
graphics commands would be interpreted in both PFSM_FLAT and PFSM_GOURAUD
shade models.
Example 1:
/*
* Draw a three-primitive triangle strip in OpenGL
*/
glColor3f(0, 0, 0); /****************************************/
glBegin(GL__TRIANGLE_STRIP);/* Actual Rendered Triangle Colors */
glVertex3v(v0); /* ------------------------------------ */
glVertex3v(v1); /* Tri PFSM_FLAT PFSM_GOURAUD */
glColor3f(1, 0, 0); /* ------------------------------------ */
glVertex3v(v2); /* 0 red black/black/red */
glColor3f(0, 1, 0); /* */
glVertex3v(v3); /* 1 green black/red/green */
glColor3f(0, 0, 1); /* */
glVertex3v(v4); /* 2 blue red/green/blue */
glEnd(); /****************************************/
Consequently, strips (triangle PFGS_TRISTRIPS or line PFGS_LINESTRIPS)
which are composed of different colored primitives must have flat shading
enabled in order to be rendered properly. The pfGeoSet primitive types
of PFGS_FLAT_TRISTRIPS and PFGS_FLAT_LINESTRIPS ensure that flat shading
will be enabled when the pfGeoSet is drawn.
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pfShadeModel(3pf) OpenGL Performer 3.2.2 libpr C++ Reference Pages
Another subtlety of the shading model is related to the current lighting
model. If the lighting model is local due to either the pfLightModel (-
pfLightModel::setLocal) or if any pfLights are local (pfLight::setPos),
then Gouraud shading must be enabled since lighting effects should be
different at each vertex. This means that even if a triangle has a
constant color and normal, it should still be drawn with Gouraud shading
so the effects of the local lighting can be seen. The exception to this
rule are the flat strips discussed above.
The shading model state element is identified by the PFSTATE_SHADEMODEL
token. Use this token with pfGeoState::setMode to set the shading model
of a pfGeoState and with pfOverride to override subsequent shading model
changes.
Example 2:
/* Set up flat shaded pfGeoState. */
gstate->setMode(PFSTATE_SHADEMODEL, PFSM_FLAT);
/* Attach gstate to gset */
gset->setGState(gstate);
/* Draw flat shaded gset */
gset->draw();
Example 3:
/* Alternative way to draw flat-shaded pfGeoSet */
gset->setDrawMode(PFGS_FLATSHADE, PF_ON);
gset->draw();
Example 4:
/*
* Draw flat-shaded triangle strip pfGeoSet. PFGS_FLATSHADE
* and pfShadeModel are not required.
*/
gset->setPrimType(PFGS_FLAT_TRISTRIPS);
gset->draw();
Example 5:
pfShadeModel(PFSM_FLAT);
/* Override shading model to PFSM_FLAT */
pfOverride(PFSTATE_SHADEMODEL, PF_ON);
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pfShadeModel(3pf) OpenGL Performer 3.2.2 libpr C++ Reference Pages
pfShadeModel is a display-listable command. If a pfDispList has been
opened by pfDispList::open, pfShadeModel will not have immediate effect
but will be captured by the pfDispList and will only have effect when
that pfDispList is later drawn with pfDispList::draw.
The selection of which shading model a pfGeoSet uses is based upon the
following decision hierarchy:
1. Use flat shading if pfGeoSet is PFGS_FLAT_TRISTRIPS or
PFGS_FLAT_LINESTRIPS or if PFGS_FLATSHADE is enabled through
pfGeoSet::setDrawMode.
2. Use the shading model set by the attached pfGeoState, if any
(see pfGeoSet::setGState).
3. Use the shading model set by pfShadeModel.
The default shading model is Gouraud.
pfGetShadeModel returns the current shading model.
NOTES
Overriding the shading model to PFSM_FLAT can be a useful debugging aid
since it reveals the facets of a normally smooth surface.
SEE ALSO
pfGSetGState, pfGeoSet, pfGeoState, pfLModelLocal, pfLightPos, pfState
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