OpenGL C Quick Reference

int glutGet( GLUT_WINDOW_WIDTH )
int glutGet( GLUT_WINDOW_HEIGHT )

Returns the width or height of the current window.

void glViewport( GLint x, GLint y, GLsizei width, 
GLsizei height )

Specifies the affine transformation of x and y from normalized device coordinates to window coordinates.

void glutReshapeFunc( void (*reshape)(int width, 
int height) )

Specifies the function to be called when the window is resized. It is used to update the viewport and viewing volume as the window changes size or aspect ratio.