An OpenGL Question
Posted: 24.08.2005, 01:39
I know there are some OpenGL gurus sitting in the shadows of these forums....so here it goes...
Can someone direct me to the right formula for plotting and positioning objects on the surface of a sphere...eg: billboard of a tree so its facing straight up and down...I thought at first that by using the sphere normals I could get this to work but I know Im going about it all wrong....
I am currently using glRotate to try to rotate the object to be straight to no avail....
These are the angle calculations I am using...
This is within a for loop i and j subdivided by a level of display from 32 to 1024...That would be n of course....
Here is the code or buffer of the billboard I am placing using vertex buffers and glRotate...
and
Can someone direct me to the right formula for plotting and positioning objects on the surface of a sphere...eg: billboard of a tree so its facing straight up and down...I thought at first that by using the sphere normals I could get this to work but I know Im going about it all wrong....
I am currently using glRotate to try to rotate the object to be straight to no avail....
These are the angle calculations I am using...
Code: Select all
angleX1 = RADTODEG(double(j) * PI / (double(n)/2));
angleX2 = RADTODEG(double(j+1) * PI / (double(n)/2));
angleY1 = RADTODEG(double(i) * TWOPI / double(n))-90;
angleY2 = RADTODEG(double(i+1) * TWOPI / double(n))-90;
This is within a for loop i and j subdivided by a level of display from 32 to 1024...That would be n of course....
Here is the code or buffer of the billboard I am placing using vertex buffers and glRotate...
Code: Select all
float obj_billboard_norm[12][3] = {0.7071, 0.0000, 0.7071,
0.7071, 0.0000, 0.7071,0.7071, 0.0000, 0.7071,
0.7071, 0.0000, 0.7071,0.7071, 0.0000, 0.7071,
0.7071, 0.0000, 0.7071,-0.7071, 0.0000, 0.7071,
-0.7071, 0.0000, 0.7071,-0.7071, 0.0000, 0.7071,
-0.7071, 0.0000, 0.7071,-0.7071, 0.0000, 0.7071,
-0.7071, 0.0000, 0.7071};
float obj_billboard_vert[12][3] = {-0.3536, 1.0000, 0.3536,
-0.3536, 0.0000, 0.3536,0.3536, 1.0000, -0.3536,
0.3536, 0.0000, -0.3536,0.3536, 1.0000, -0.3536,
-0.3536, 0.0000, 0.3536,-0.3536, 1.0000, -0.3536,
-0.3536, 0.0000, -0.3536,0.3536, 1.0000, 0.3536,
0.3536, 0.0000, 0.3536,0.3536, 1.0000, 0.3536,
-0.3536, 0.0000, -0.3536};
float obj_billboard_tex[12][3] = {0.9995, 0.9995,
0.9995, 0.0005,0.0005, 0.9995,
0.0005, 0.0005,0.0005, 0.9995,
0.9995, 0.0005,0.0000, 1.0000,
0.0000, 0.0000,1.0000, 1.0000,
1.0000, 0.0000,1.0000, 1.0000,
0.0000, 0.0000};
and
Code: Select all
void Sphere::drawTree(float radius, Vec3d pos, Vec3d rot)
{
glPushMatrix();
glTranslated(pos.x,pos.y,pos.z);
glRotated(rot.x, 1.0, 0.0, 0.0);
glRotated(rot.y, 0.0, 1.0, 0.0);
glRotated(rot.z, 0.0, 0.0, 1.0);
glEnable(GL_NORMALIZE);
glScaled(radius, radius, radius);
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState (GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer (2, GL_FLOAT, 0, obj_billboard_tex);
glNormalPointer (GL_FLOAT, 0, obj_billboard_norm);
glVertexPointer (3, GL_FLOAT, 0, obj_billboard_vert);
glDrawArrays(GL_TRIANGLES, 0, 12);
glDisableClientState (GL_VERTEX_ARRAY);
glDisableClientState (GL_NORMAL_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisable(GL_NORMALIZE);
glPopMatrix();
}