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Game Size and the Sprite Atlas

November 21, 2017

A sprite atlas is a sheet holding more than one sprite. It is supposed to be more efficient for the graphics engine to use. For our purposes, it is also useful for reducing program size. For Goblin Defence I was able to cut size from 118Mb down to 59Mb.


Using a sprite was easy. Just change calls to "Resource.Load(path)" to "atlas.GetSprite(name)". Since the atlas only knows the name, I did need to rename sprites with the same name but on different paths.


In Goblin Defence sprites were sometimes used to hold Texture2D textures for other purposes. A sprite contains the offset into the atlas. There is no built-in function at run-time to copy the texture. I had to write one.


  public static Texture2D GetTexture(Sprite sprite) {
    if (!sprite.packed) {
      return sprite.texture; // not in atlas
    int x = (int)System.Math.Ceiling(sprite.textureRect.x)

    int y = (int)System.Math.Ceiling(sprite.textureRect.y);

    int width = (int)System.Math.Ceiling(sprite.textureRect.width);

    int height = (int)System.Math.Ceiling(sprite.textureRect.height);

    Texture2D texture = new Texture2D (width, height);
    texture.SetPixels(sprite.texture.GetPixels(x, y, width, height));
    return texture;


Have a look at the results while playing Goblin Defence.




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