Global Texture

OpenGL Development
#1

So I’ve got a large image of several sprites. Instead of loading that whole texture in every single class that uses a sprite from the image, I’d like to load it once at the beginning of my program, and have it accessible by all classes. How might I go about doing this? (I’m using the slick-util library for textures.)

#2

Here are two common/easy ways. One would be to rely on static getters or singleton instances. You can extend this however you see fit; e.g. storing your textures by a String identifier in a hash map.

MyEntity {
    Texture texture;

    public MyEntity() {
        //gets the already-loaded texture
        this.texture = MyResources.getInstance().getMyTexture();
    }
}

Another common solution is to pass the single texture to the entity when you create it:

MyEntity {
    Texture texture;

    public MyEntity(Texture texture) {
        this.texture = texture;
    }
}

To draw a “sub image” of a texture (i.e. render a particular sprite in a sheet), you need to define your texcoords properly. With slick-util, you might define an Image2D/Sprite class that holds the normalized texture offsets and width/height that will be passed to glTexCoord2f:

	public Image2D(Texture texture) {
		this.texture = texture;
		this.normalizedWidth = texture.getWidth();
		this.normalizedHeight = texture.getHeight();
		this.width = texture.getImageWidth();
		this.height = texture.getImageHeight();
		this.centerX = width / 2f;
		this.centerY = height / 2f;
	}

	public Image2D getSubImage(float x, float y, float width, float height) {
		float tx = ( x / this.width * normalizedWidth ) + textureOffsetX;
		float ty = ( y / this.height * normalizedHeight ) + textureOffsetY;
		float tw = width / this.width * normalizedWidth;
		float th = height / this.height * normalizedHeight;
		
		Image2D img = copy();
		img.textureOffsetX = tx;
		img.textureOffsetY = ty;
		img.width = width;
		img.height = height;
		img.normalizedWidth = tw;
		img.normalizedHeight = th;
		img.centerX = width / 2f;
		img.centerY = height / 2f;
		return img;
	}
#3

I already knew how to divide the texture, I just needed to know how to pass it between classes. Anyways, you answered my question. Much appreciated!

#4

It might heresy for some but just slap those on public static fields on some place.
Work everytime without any effort.

#5

That’s what I tried initially. I can’t remember why it didn’t work, and I’m too tired to try it again (It’s 1:00 am here.) I’ll try it when I wake up, and let you know how it goes. :slight_smile: Thanks!