You can specify a UV Rectangle that will control which part of the texture will be drawn. X and Y control the UV offset, and W and H control the width and height of the UVs (texture coordinates). Like all texture coordinates, these values are usually 0 to 1 (with 0 meaning one side of the texture and 1 meaning the other). The UVs are bottom-left based, so if you wanted to draw the top 50% of the texture you'd specify UV Rectangle of (0, 0.5, 1, 0.5).
