OpenGL Hemisphere Texture Mapping - c++

Question

I need to have a hemisphere in opengl. I found a drawSphere function which I modified to draw half the lats (which ends up drawing half of the sphere) which is what I wanted. It does this correctly.
However, I don't know what i should do with glTexCoordf to get the textures to map properly onto this half sphere. I'm really not great with opengl, and I've tried countless variations but I just can't get the textures to appear properly on it.
void drawHemisphere(double r, int lats, int longs)
{
int i, j;
int halfLats = lats / 2;
for(i = 0; i <= halfLats; i++)
{
double lat0 = M_PI * (-0.5 + (double) (i - 1) / lats);
double z0 = sin(lat0);
double zr0 = cos(lat0);
double lat1 = M_PI * (-0.5 + (double) i / lats);
double z1 = sin(lat1);
double zr1 = cos(lat1);
glBegin(GL_QUAD_STRIP);
for(j = 0; j <= longs; j++)
{
double lng = 2 * M_PI * (double) (j - 1) / longs;
double x = cos(lng);
double y = sin(lng);
// glTexCoordf()
glNormal3f(x * zr0, y * zr0, z0);
glVertex3f(x * zr0, y * zr0, z0);
// glTexCoordf()
glNormal3f(x * zr1, y * zr1, z1);
glVertex3f(x * zr1, y * zr1, z1);
}
glEnd();
}
}
Does anyone have any idea of what values I should be putting in? Or what I need to calculate for it?
Thanks!

Answer 1

Basically, you shouldn't need anything fancy there. The texture coordinate space ranges from zero to one. So pick some intermediate values for the vertices in between. I can't explain it more thoroughly without image, so the best I can do is to point You to this article: UV mapping, it's a good starting point. Hope this helps as a starter.
Here's my guess:
{
double lng = 2 * M_PI * (double) (j - 1) / longs;
double x = cos(lng);
double y = sin(lng);
double s1, s2, t;
s1 = ((double) i) / halfLats;
s2 = ((double) i + 1) / halfLats;
t = ((double) j) / longs;
glTexCoord2d(s1, t);
glNormal3d(x * zr0, y * zr0, z0);
glVertex3d(x * zr0, y * zr0, z0);
glTexCoord2d(s2, t);
glNormal3d(x * zr1, y * zr1, z1);
glVertex3d(x * zr1, y * zr1, z1);
}
Remember to properly set texture in OpenGL. An example call with texture:
glActiveTexture(GL_TEXTURE0);
glMatrixMode(GL_TEXTURE);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
// texture must be bound & enabled
texture.bind();
texture.enable();
drawHemisphere(1, 40, 40);
texture.disable();
I used Java + JOGL to test it, so it's not one-to-one C++ solution, but conceptually it should be the same. At least You have proper glTexCoord2d() calls.