Question

GL_TRIANGLE_STRIP

Asked by: xargon_123

Hi everyone,

I am drawing some vertices around a primitive using glDrawArrays like:

glDrawArrays(GL_TRIANGLE_STRIP, 0, verticesArray);

However, the primitive drawn is very jagged and looks terrible. I tried
enabling anti-aliasing, but that does not help. I tried increasing the
number of points in the vertices array, but it still does not make a
difference. I was wondering if someone can help me with it. Here is
some sample code:

#define M_PI 3.1415926535897932f
int GUI_div = 20;

divinc = M_PI/GUI_div;

        // calculate coords
        for(i = 0, angle = 0.0; angle < M_PI+.01; i++, angle += divinc)
        {
                // inside
                pos[i][0] = (float)sin(angle) + button->width*0.5f;
                pos[GUI_div+GUI_div+1-i][0] = -pos[i][0];
                pos[GUI_div+GUI_div+1-i][1] = pos[i][1] = (float)cos(angle);
                pos[GUI_div+GUI_div+1-i][2] = pos[i][2] = 0.0f;
        }

    glEnable(GL_LINE_SMOOTH);
        glBegin(GL_TRIANGLE_FAN);
        for(i=0; i<GUI_div+GUI_div+2; i++)
        {
                glTexCoord2fv(tpos[i]);
                glVertex3fv(pos[i]);
        }
        glEnd();
    glDisable(GL_LINE_SMOOTH);

increasing the GUI_DIV parameter does not seem to have any effect,
neither does the anti-aliasing command...

Would appreciate any help :)

Thanks

-L

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Asked On
2005-12-10 at 03:48:48ID21660069
Tags

gl_triangle_strip

Topic

OpenGL Graphics & Game Programming

Participating Experts
2
Points
500
Comments
2

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Answers

 

by: ikeworkPosted on 2005-12-10 at 04:38:09ID: 15458373

hi xargon,

do you use the lighting? if so, you will need to define normals for your vertices too.
this can make surfaces much smoother...
depending on the kind of surface, you can use normal-interpolation to get better effects too...

ike

 

by: davebytesPosted on 2005-12-12 at 08:11:58ID: 15467227

do you mean to be drawing a 2D primitive or a 3D one?  If 2D, drop the z coord and use glVertex2fv.

Now, as for 'jagged', you'd need to provide a link to a picture.  I can imagine you are rendering a disc, and it doesn't look as smooth as you'd like -- but I don't know if you mean 'jagged' as at-the-vertices, or 'jagged' as in the-triangle-edges?

If I read this correct, you are creating a 20-sided disc approximation.  that's 5 triangles per quarter, 18 degrees per triangle.  That's not a very smooth arc.  You want smooth?  Try using using more like 3 degrees per triangle (which would == 120 triangles vs your 20), or more.  That should work.  If it makes no difference, then something else is very wrong.  (20 vs 120 should be an immediate, visible difference.  have it render BOTH side by side, you should see the difference...).

-d

20120131-EE-VQP-002

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