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# Does anyone know how to draw spheres?

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5 replies to this topic

### #1Coaster15  Members

Posted 15 April 2000 - 12:22 PM

I am working w/ openGL and can''t figure out a way to draw spheres, you can draw circles point by point w/ (cos,sin) but how about spheres, is their an easy way, or is their no way at all?

### #2Mezz  Members

Posted 15 April 2000 - 12:38 PM

look into the draw functions supplied with libs such as glut or glu/glaux.

They have some advanced drawing functions like teapots and spheres, I cannot remember the stuff offhand though.

-Mezz

### #3a2k  Members

Posted 15 April 2000 - 12:39 PM

i think think glu.h has a glusphere(), but check
i KNOW that the glut library has a glutSolidSphere(radius, segments x, segments y)

a2k

### #4ga  Members

Posted 15 April 2000 - 12:40 PM

There is a way, of course.
If you draw a circle, you set x=r*cos(t) and y=r*sin(t).
If you want do draw a sphere you have to add a second angle and to scale x and y by the cosine of this angle:
x=r*cos(t)*cos(s)
y=r*sin(t)*cos(s)
z=r*sin(s)

GA

### #5xeos  Members

Posted 15 April 2000 - 01:03 PM

Simple -- use the gluSphere. Simply set up a new gluQuadricObj, and pass the other variables

NOTE: You must include and link to the GLU libraries!!!

This is probably the fastest method for doing this. However, there are pleanty of other methods. Why not try an iterative provcess.

Start at the top. (0,1,0) (OBJECT COORDS)
Plot a pixel.
Come down by curved distance between (0,1,0) and (0,-1,0), cd, divided by interval.
Find the distance from y axis -- this is the radius of a circle at that y-value.
Now, draw a circle there, and repeat the process.

Gotta go (I''m climbing trees!)

Simon

### #6ga  Members

Posted 04 May 2000 - 03:16 AM

Here's some pseudo-code:
 for(s=0;s<=360;s++) for(t=-90;t<=90;t++) { SphereVertex[s][90+t].x = r*cos(t*PI/180)*cos(s*PI/180); SphereVertex[s][90+t].y = r*sin(t*PI/180)*cos(s*PI/180); SphereVertex[s][90+t].z = r*sin(s*PI/180); } 
Then you can draw the triangles made of vertices [0][0],[1][0],[0][1] and [1][0],[1][1],[0][1] ........
and you can use s/360 and (t+90)/180 as texture coordinates if you have got a mercator-projected map.