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render unit sphere 2D, OpenGL

Posted on 2008-10-07
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Last Modified: 2013-12-06
Hey people, I need help rendering a unit sphere to a 2d img. by using the setpixel f'n. It is a 256 x 256.

This below only helps by covering all pixels and shading it white...

for (int x=0; x < 256; x++) {
            for (int y = 0; y < 256; y++) {
              int Px = ((x/128) - 1);
                   int Py = ((y/128) - 1);
              int Pz = sqrt(Px*Px);
                    if (sqrt(Px*Px + Py*Py) < 1)
                  img.setPixel(x, y, Pixel(1.0, 1.0, 1.0));
            
            }

      }

I also have to do lighting to shade this to make it look 3D..
Any help will be greatly appreciated! Thanks!
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Question by:MANNYWOOD
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Expert Comment

by:jose_juan
ID: 22666726
Hi MANNYWOOD,

to simulate 2D render use a glOrtho proyection matrix, in any case, you must use 3D real objects to compund your scene.

Before scene are rendered then get all viewport pixels with glReadPixels.

I think you don't need a realtime execution, in other case, (this way not is bad but) better (and complex) methods are available.

Do you need a explained example?

Good luck!
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Author Comment

by:MANNYWOOD
ID: 22666840
I'm not too sure still...
The form/ skeleton is already given with the projection, viewing and drawing of the matrix.
I guess when I mean the below only helps by covering all pixels and shading it white, that is the top left box in openGL which has a 256x256 setting and also allows mouse controls to cover pixels in the area. I guess representing a circle really isn't that easy in openGL.

An explained example will defenitley help!, that is.. if you don't mind.
Thanks again jose_juan!
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Accepted Solution

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jose_juan earned 125 total points
ID: 22666891
Uhm... ;-)

in OpenGL, all objects must be 3D (really not, but suppose it) if you like a circle then, Draw a toroids!

I recommend to you don't think in pixels units, better in frustum (or viewport) units.

Here a good page for create toroids at runtime.

http://www.gamedev.net/reference/articles/article1172.asp

Good luck!
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Author Comment

by:MANNYWOOD
ID: 22666927
Thanks~ Hopefully I could understand this.
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