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?

# Does anyone know how to draw spheres?

Started by Coaster15, Apr 15 2000 12:22 PM

5 replies to this topic

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#4
Members - Reputation: **126**

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)

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GA

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)

Visit our homepage: www.rarebyte.de.st

GA

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#5
Members - Reputation: **122**

Posted 15 April 2000 - 01:03 PM

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

void gluSphere( GLUquadricObj *qobj, GLdouble radius, GLint slices, GLint stacks);

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

void gluSphere( GLUquadricObj *qobj, GLdouble radius, GLint slices, GLint stacks);

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

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#6
Members - Reputation: **126**

Posted 04 May 2000 - 03:16 AM

Here's some pseudo-code:

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.

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GA

Edited by - ga on 5/4/00 9:17:46 AM

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.

Visit our homepage: www.rarebyte.de.st

GA

Edited by - ga on 5/4/00 9:17:46 AM