Resizing an OpenGL window causes it to fall apart - c++

Question

For some reason when I resize my OpenGL windows, everything falls apart. The image is distorted, the coordinates don't work, and everything simply falls apart. I am sing Glut to set it up.
//Code to setup glut
glutInitWindowSize(appWidth, appHeight);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
glutCreateWindow("Test Window");
//In drawing function
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClear(GL_COLOR_BUFFER_BIT);
//Resize function
void resize(int w, int h)
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, w, h, 0);
}
The OpenGL application is strictly 2D.
This is how it looks like initially: http://www.picgarage.net/images/Corre_53880_651.jpeg
this is how it looks like after resizing: http://www.picgarage.net/images/wrong_53885_268.jpeg

Answer 1

You should not forget to hook the GLUT 'reshape' event:
glutReshapeFunc(resize);
And reset your viewport:
void resize(int w, int h)
{
glViewport(0, 0, width, height); //NEW
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, w, h, 0);
}
A perspective projection would have to take the new aspect ratio into account:
void resizeWindow(int width, int height)
{
double asratio;
if (height == 0) height = 1; //to avoid divide-by-zero
asratio = width / (double) height;
glViewport(0, 0, width, height); //adjust GL viewport
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(FOV, asratio, ZMIN, ZMAX); //adjust perspective
glMatrixMode(GL_MODELVIEW);
}