// Given three points on a plane in counter clockwise order, calculate the unit normal
void gltGetNormalVector(const GLTVector3 vP1, const GLTVector3 vP2, const GLTVector3 vP3, GLTVector3 vNormal)
{
GLTVector3 vV1, vV2;
gltSubtractVectors(vP2, vP1, vV1);
gltSubtractVectors(vP3, vP1, vV2);
gltVectorCrossProduct(vV1, vV2, vNormal);
gltNormalizeVector(vNormal);
}
// For best results, put this in a display list
// Draw a torus (doughnut) at z = fZVal... torus is in xy plane
void gltDrawTorus(GLfloat majorRadius, GLfloat minorRadius, GLint numMajor, GLint numMinor)
{
GLTVector3 vNormal;
double majorStep = 2.0f*GLT_PI / numMajor;
double minorStep = 2.0f*GLT_PI / numMinor;
int i, j;
for (i = 0; i<numMajor; ++i)
{
double a0 = i * majorStep;
double a1 = a0 + majorStep;
GLfloat x0 = (GLfloat)cos(a0);
GLfloat y0 = (GLfloat)sin(a0);
GLfloat x1 = (GLfloat)cos(a1);
GLfloat y1 = (GLfloat)sin(a1);
glBegin(GL_TRIANGLE_STRIP);
for (j = 0; j <= numMinor; ++j)
{
double b = j * minorStep;
GLfloat c = (GLfloat)cos(b);
GLfloat r = minorRadius * c + majorRadius;
GLfloat z = minorRadius * (GLfloat)sin(b);
// First point
glTexCoord2f((float)(i) / (float)(numMajor), (float)(j) / (float)(numMinor));
vNormal[0] = x0*c;
vNormal[1] = y0*c;
vNormal[2] = z / minorRadius;
gltNormalizeVector(vNormal);
glNormal3fv(vNormal);
glVertex3f(x0*r, y0*r, z);
glTexCoord2f((float)(i + 1) / (float)(numMajor), (float)(j) / (float)(numMinor));
vNormal[0] = x1*c;
vNormal[1] = y1*c;
vNormal[2] = z / minorRadius;
glNormal3fv(vNormal);
glVertex3f(x1*r, y1*r, z);
}
glEnd();
}
}
