Sometimes it makes sense to use existing texture as font glyphs atlas.

For example, if you make a GUI library that uses FontStashSharp, it makes sense to pass an existing texture that holds GUI images to the FontSystem. This approach is good for performance because it minimizes the amount of texture swaps, since both GUI images and glyphs will be stored on a single texture.

This can be achieved using the following code:

  var settings = new FontSystemSettings
  {
    ExistingTexture = texture,
    ExistingTextureUsedSpace = new Rectangle(0, 0, 160, 1024) // Rectangle that covers area already used by the GUI images
  };

  var fontSystem = new FontSystem(settings);

Now this fontSystem will use texture to store the font glyphs. It'll place them outside of the ExistingTextureUsedSpace. If the space on the texture will run out, then FontStashSharp will create new texture of same size and place the new glyphs there.