This functions is used to compute and set the global scale factor to a value that will automatically scale the scene (up or down) as if the screen width would always be width
pixels tall.
In other words, if the original scene width is width
pixels, it will always fit the entire scene in screen automatically.
SetFixedWidth(512.0f);
The example above does the exact same thing as the example below:
SetScaleFactor(GetScreenSize().x / 512.0f);