Aspect Ratio Stretching in OpenGL

Question

I am having some trouble with full screen mode. I can set my window to be 800x600, but when I full screen that resolution, it stretches. I assume this is because of a change in aspect ratio. How can I fix this? Edit #1 Here's a screen shot of what I see happening. Left: 800x600 Right: 1366x768 Edit #2 My initGraphics function gets called every time I re-size the window (WM_SIZE). ``` void initGraphics(int width, int height) { float aspect = (float)width / (float)height; glViewport(0, 0, width, height); glEnable(GL_TEXTURE_2D); glEnable(GL_BLEND); //Enable alpha blending glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); glClearColor(0.0, 0.0, 0.0, 1.0); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluOrtho2D(0.0, width, height * aspect, 0.0); glMatrixMode(GL_MODELVIEW); } ```

Accepted Answer

SOLUTION: The real problem ended up being that you were misusing the gluOrtho2D function. Instead of using this:

```
gluOrtho2D(0.0, width, height * aspect, 0.0);
```

You needed to switch it to the correct form this:

```
gluOrtho2D(0.0, width, 0.0, height);
```

The latter creates a 2D orthographic projection, that fills the entire width and height of your viewport, so no stretching occurs.

ORIGINAL ANSWER:

You need to modify your projection in order to account for the new aspect ratio.

Make sure you first of all set `glViewport` to the new window size. After the viewport is set you will need to switch your matrix mode to projection with a call to `glMatrixMode` and then finally calculate your new aspect ratio with `width / height` and pass the new aspect ratio to `gluPerspective`. You can also use straight `glFrustum` instead of `gluPerspective` you can find source to `gluPerspective` to achieve that same effect with `glFrustum`.

Something like this:

```
    float aspectRatio = width / height;
    glMatrixMode(GL_PROJECTION_MATRIX);
    glLoadIdentity();
    gluPerspective(fov, aspectRatio, near, far); 
```

Aspect Ratio Stretching in OpenGL

Solution

Problem