问题
It's pretty hard to render the data I generate, if I want to use one vertex array format only.
I tried to provide GLU_TESS_EDGE_FLAG_DATA callback, but it made my program crash. (also tried without "_DATA" in end, same effect).
How can I get it to generate GL_TRIANGLES only?
回答1:
gluTessCallback(), GLU_TESS_EDGE_FLAG
:
... if a non-NULL edge flag callback is provided ... fans and strips are converted to independent triangles.
This is what I've been using:
struct TessContext
{
~TessContext()
{
for( size_t i = 0; i < combined.size(); ++i )
{
delete[] combined[i];
}
}
typedef std::pair< double, double > Point;
std::vector< Point > pts;
std::vector< GLdouble* > combined;
};
#ifndef CALLBACK
#define CALLBACK __stdcall
#endif
void CALLBACK tess_begin( GLenum ) {}
void CALLBACK tess_edgeFlag( GLboolean ) {}
void CALLBACK tess_end() {}
void CALLBACK tess_vertex
(
void* data,
TessContext* ctx
)
{
GLdouble* coord = (GLdouble*)data;
ctx->pts.push_back( TessContext::Point( coord[0], coord[1] ) );
}
void CALLBACK tess_combine
(
GLdouble coords[3],
void* vertex_data[4],
GLfloat weight[4],
void** outData,
TessContext* ctx
)
{
GLdouble* newVert = new GLdouble[3];
ctx->combined.push_back( newVert );
newVert[0] = coords[0];
newVert[1] = coords[1];
newVert[2] = coords[2];
*outData = newVert;
}
template< typename Vec >
std::vector< Vec > Triangulate
(
const vector< Vec >& aSimplePolygon
)
{
std::vector< GLdouble > coords;
for( size_t i = 0; i < aSimplePolygon.size(); ++i )
{
coords.push_back( aSimplePolygon[i].x() );
coords.push_back( aSimplePolygon[i].y() );
coords.push_back( 0 );
}
GLUtesselator* tess = gluNewTess();
gluTessCallback( tess, GLU_TESS_BEGIN, (void (CALLBACK *)()) tess_begin );
gluTessCallback( tess, GLU_TESS_EDGE_FLAG, (void (CALLBACK *)()) tess_edgeFlag );
gluTessCallback( tess, GLU_TESS_VERTEX_DATA, (void (CALLBACK *)()) tess_vertex );
gluTessCallback( tess, GLU_TESS_END, (void (CALLBACK *)()) tess_end );
gluTessCallback( tess, GLU_TESS_COMBINE_DATA, (void (CALLBACK *)()) tess_combine );
gluTessNormal( tess, 0.0, 0.0, 1.0 );
TessContext ctx;
gluTessBeginPolygon( tess, &ctx );
gluTessBeginContour( tess );
for( size_t i = 0; i < aSimplePolygon.size(); ++i )
{
gluTessVertex( tess, &coords[i*3], &coords[i*3] );
}
gluTessEndContour( tess );
gluTessEndPolygon( tess );
gluDeleteTess(tess);
std::vector< Vec > ret( ctx.pts.size() );
for( size_t i = 0; i < ret.size(); ++i )
{
ret[i].x() = static_cast< Vec::Scalar >( ctx.pts[i].first );
ret[i].y() = static_cast< Vec::Scalar >( ctx.pts[i].second );
}
return ret;
}
I tend to use Eigen::Vector2f for Vec
.
来源:https://stackoverflow.com/questions/12600325/force-glutesselator-to-generate-only-gl-triangles