code: public void addQuad (Texture tex, int tint, AffineTransform xf,
                         float dx, float dy, float dw, float dh,
                         float sx, float sy, float sw, float sh) {
      setTexture(tex);
      float texWidth = tex.displayWidth, texHeight = tex.displayHeight;
      addQuad(tint, xf, dx, dy, dx+dw, dy+dh,
              sx/texWidth, sy/texHeight, (sx+sw)/texWidth, (sy+sh)/texHeight);
    }
docs: Adds {@code tex} as a transformed axis-aligned quad to this batch.
  {@code dx, dy, dw, dh} define the size and position of the quad.
  {@code sx, sy, sw, sh} define region of the texture which will be displayed in the quad.