Question

I’m developing C++ OpenGL code in Windows using Visual Studio 2008. I can’t for the life of me understand why none of the integer functions work. I’ll try using glVertex2i(2,2) but all I get is a black screen, I’ve also tried this with glrecti but I have had the same result.

When I use the floating point functions, they work. glVertex2f(.5,.5) and glRectf(1,2,3,4) work fine. I just can’t figure out what is going wrong, what I have missed. People have obviously used glVertex2i before and had it work.

The simple code I’ve been working off of is this:

#include <windows.h>
#include <gl/gl.h>
#include <gl/glu.h> 
#include <gl/glut.h>

void draw(){   
  glClearColor(0,0,0,1);
  glClear( GL_COLOR_BUFFER_BIT );
  glColor3f(1, 1, 1); 
  glBegin(GL_LINES);
  glVertex2i(100,100);  
  glVertex2i(200,200);
  glEnd();
  glFlush(); 
}

int main(int argc, char** argv){   
  glutInit(&argc, argv);  
  glutInitWindowSize(600, 600);
  glutCreateWindow("My first OpenGL program");    
  glutDisplayFunc(draw);  
  glutMainLoop();
}

Answer 1

Your code doesn’t set any projection matrices, so passing values outside [-1, 1] is drawing outside of the viewport. That’s why integer functions “don’t work”.