[vox-tech] opengl: lines and points

[Ken Bloom]

On Sun, 30 Jan 2005 00:49:56 -0500
p at dirac.org (Peter Jay Salzman) wrote:

>    #include <GL/glut.h>
> 
>    void display(void)
>    {
>       glClear (GL_COLOR_BUFFER_BIT);
> 
>       glBegin( GL_LINES );
>          glColor3f( 1.0, 0.0, 0.0 );     // *1*
>          glVertex2f( 400.0f, 50.0f );    // *1*
>          glVertex2f( 400.0f, 550.0f );   // *1*
> 
>          glColor3f( 1.0, 1.0, 1.0 );     // *2*
>          glVertex2f( 50.0f, 300.0f );    // *2*
>          glVertex2f( 750.0f, 300.0f );   // *2*
>       glEnd();
> 
>       glFlush();
>    }
> 
>    int main(int argc, char *argv[])
>    {
>       glutInit(&argc, argv);
>       glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
>       glutInitWindowSize (800, 600); 
>       glutInitWindowPosition (100, 100);
>       glutCreateWindow (argv[0]);
> 
>       glClearColor (0.0, 0.0, 0.0, 0.0);
>       glShadeModel (GL_FLAT);
> 
>       glutDisplayFunc(display); 
> 
>       glutMainLoop();
>       return 0;
>    }

I'm not sure why it shows up for you when you deleted one of the lines,
but when I ran your code as written, the lines were outside the
(-1.0,-1.0) to (1.0,1.0) clipping box, so they weren't getting drawn.
Changing the coordinates helped, and they were both drawn. The second
one was white though (use glColor3f( 0.0, 0.0, 1.0 ); if you want blue).

--Ken Bloom

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