Resizing an OpenGL window causes it to fall apart

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

The images are no longer available.

Nick Caplinger
– Nick Caplinger

2013-08-19 18:56:01 +00:00
Commented Aug 19, 2013 at 18:56 — Nick Caplinger
– Nick Caplinger, Commented Aug 19, 2013 at 18:56

aib · Accepted Answer · 2009-03-15 22:02:16Z

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); }

And replace the C-style cast with static_cast<> since you're working with C++ :)

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