Hello,
I downloaded the moon texture from
this page (at the bottom) and tried mapping it to a sphere, constructing the vertex and texture coordinates myself (well, in code, but not using any special API calls for spheres...). However, the texture converges badly towards the poles:
I am using quads, equidistant in x, and stretched by sin in y (so y differences are smaller towards the poles). I get the same effect with equidistant y coordinates. I use this method as well for texture coordinates as for vertex coordinates, where the vertices converge by shrinking the radius of the resultic cylinder. I hope you understand this - the code is a bit convoluted, but you may want to have a look anyway:
for (int x = 0; x <= max_x; ++x)
{
for (int y = 0; y <= max_y; ++y)
{
int dy = max_y - y;
float d = r;
d = sin((M_PI / 2) + y * (M_PI / 2) / (float)max_y);
// construct upper half
coords[x][max_y - y].x = d * sin(x * (2 * M_PI / (float)max_x));
coords[x][max_y - y].y = r * sin(y * M_PI / 2 / (float)max_y);
coords[x][max_y - y].z = d * cos(x * (2 * M_PI / (float)max_x));
double yf = y / ((float)max_y * 2.0);
yf = sin(y * M_PI / 2 / (float)max_y) / 2;
coords[x][max_y - y].u = x / ((float)max_x );
coords[x][max_y - y].v = 0.5 - yf;
// lower half
coords[x][max_y + y].x = coords[x][max_y - y].x;
coords[x][max_y + y].y = -coords[x][max_y - y].y;
coords[x][max_y + y].z = coords[x][max_y - y].z;
coords[x][max_y + y].u = coords[x][max_y - y].u;
coords[x][max_y + y].v = 0.5 + yf;
}
}
Now the question is, can this texture be mapped better, what do you think by looking at it? What would be the correct formula? I'd appreciate any hint, as these are my first steps (using Open GL) :)
Thanks! :)
