Draw random points

Question

I have a window size {0,0},{1e6,1e6}. I have created grids of 1000*1000 within this area.
I am trying to create random points in this area.

glEnable( GL_POINT_SMOOTH );
glEnable( GL_BLEND );
glPointSize( 200 );
for( int i = 0; i < 1e6; i++ )
{
    glColor3ub(0,255,0);
    // width and height are 1e6.
    int x = rand() % WIDTH; 
    int y = rand() % HEIGHT; 
    glBegin( GL_POINTS );
    glVertex2i( x, y );
    glEnd();
}
glFlush();  
glDisable( GL_BLEND );

x and y are random numbers. However, all points are drawn only in left bottom of the window.

Did you call glViewport? What were the arguments to it? You're viewport might not be the rectangle (0, 0)->(WIDTH, HEIGHT) — Jacob Parker, Oct 10 '12 at 19:14
I have passed the actual width and height. Random numbers generated i guess are too small so they are appearing only in the bottom left corner. I want evenly distributed points. Could you please tell me if there is any better approach? — user1302064, Oct 10 '12 at 19:38
x = rand()/(float)RAND_MAX; y= rand()/(float)RAND_MAX; discs[i].x=x*WIDTH; discs[i].y=y*HEIGHT;Thank you so much. With this code it worked — user1302064, Oct 10 '12 at 21:39

score 0 · Answer 1 · edited May 23 '17 at 12:18

0

Ensure that RAND_MAX on your platform is greater than 1e6. Otherwise the largest x/y value you will see will be RAND_MAX-1, not 1e6 as you're expecting.

Or generate random numbers without modulo.

edited May 23 '17 at 12:18

Community

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answered Oct 10 '12 at 16:20

genpfault

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Draw random points

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