Question

I am creating a simple 2D OpenGL application but I seem to be experiencing some camera issues. When I draw a rectangle at (20,20) it is drawn at (25,20) or so. When I draw it at (100, 20) it is drawn at 125 or so. For some reasons everything is being shifted to the right by a few %.

I have pasted a trimmed down version here http://pastebin.com/m56491c4c

Is there something wrong with the way I am setting up GLUT? I know it’s not my objects doing anything weird since the same thing happens when I disable them.

Thanks in advance.

Answer 1

You need to set the projection matrix inside the reshape function (resize()), which also automatically solves the problem of the user resizing the window:

void resize(int w, int h) {   glMatrixMode(GL_PROJECTION);   glLoadIdentity();   gluOrtho2D(0, w, h, 0); } 

And then in your draw function, make sure that the matrix mode is model-view:

void draw() {   glMatrixMode(GL_MODELVIEW);   glLoadIdentity();   ... } 

Other problems with your code:

• You probably shouldn’t be calling glutPostRedisplay() at the end of draw(). This is going to make your CPU run at 100%. You can instead use glutTimerFunc() to still have updates every some number of milliseconds.
• In processMouse(), you’re using wsprintf() on an array of chars: wsprintf() takes an array of wide characters (wchar_t), so you should make the local variable s of type wchar_t[], or use sprintf() and MessageBoxA() instead of wsprintf() and MessageBoxW() (to which MessageBox() expands as a macro when compiling a Unicode application, which I’m assuming you’re doing). You’re also vulnerable to a buffer overflow — you should use a buffer of at least 12 characters, even though realistically you’ll never be passed a very large x value. Finally, you should also use snprintf()/wsnprintf() instead of sprintf()/wsprintf() to protect against the buffer overflow.