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Faster triangle area routine contributed by Norman Vine.

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curt 2000-12-05 20:20:57 +00:00
parent 174553feef
commit 3ec542d18f
2 changed files with 33 additions and 3 deletions
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4
FlightGear.dsp
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@ -2663,7 +2663,7 @@ SOURCE=.\src\Scenery\hitlist.cxx
# End Source File
# Begin Source File
SOURCE=.\src\Scenery\scenery.cxx
SOURCE=.\src\Scenery\newcache.cxx
!IF "$(CFG)" == "FlightGear - Win32 Release"
@ -2678,7 +2678,7 @@ SOURCE=.\src\Scenery\scenery.cxx
# End Source File
# Begin Source File
SOURCE=.\src\Scenery\tilecache.cxx
SOURCE=.\src\Scenery\scenery.cxx
!IF "$(CFG)" == "FlightGear - Win32 Release"

32
src/Objects/obj.cxx
View file

@ -267,6 +267,35 @@ ssgBranch *fgGenTile( const string& path, FGTileEntry *t) {
}
static float sgTriArea( sgVec3 p0, sgVec3 p1, sgVec3 p2 ) {
/*
From comp.graph.algorithms FAQ
2A(P) = abs(N.(sum_{i=0}^{n-1}(v_i x v_{i+1})))
*/
sgVec3 sum;
sgZeroVec3( sum );
sgVec3 norm;
sgMakeNormal( norm, p0, p1, p2 );
float *vv[3];
vv[0] = p0;
vv[1] = p1;
vv[2] = p2;
for( int i=0; i<3; i++ ) {
int ii = (i+1) % 3;
sum[0] += (vv[i][1] * vv[ii][2] - vv[i][2] * vv[ii][1]) ;
sum[1] += (vv[i][2] * vv[ii][0] - vv[i][0] * vv[ii][2]) ;
sum[2] += (vv[i][0] * vv[ii][1] - vv[i][1] * vv[ii][0]) ;
}
return( sgAbs(sgScalarProductVec3( norm, sum )) * SG_HALF );
}
#if 0
// this works too, but Norman claims sgTriArea() is more efficient :-)
static double triangle_area_3d( float *p1, float *p2, float *p3 ) {
// Heron's formula: A^2 = s(s-a)(s-b)(s-c) where A is the area,
// a,b,c are the side lengths, s=(a+b+c)/2. In R^3 you can compute
@ -280,6 +309,7 @@ static double triangle_area_3d( float *p1, float *p2, float *p3 ) {
return sqrt( s * ( s - a ) * ( s - b ) * ( s - c ) );
}
#endif
static void random_pt_inside_tri( float *res,
@ -316,7 +346,7 @@ static void gen_random_surface_points( ssgLeaf *leaf, ssgVertexArray *lights,
p1 = leaf->getVertex(n1);
p2 = leaf->getVertex(n2);
p3 = leaf->getVertex(n3);
double area = triangle_area_3d( p1, p2, p3 );
double area = sgTriArea( p1, p2, p3 );
double num = area / factor;
// generate a light point for each unit of area