code: void draw(GLShader shader, InternalTransform xform, int tint,
              float dx, float dy, float dw, float dh, float sx, float sy, float sw, float sh) {
      float texWidth = width(), texHeight = height();
      drawImpl(shader, xform, ensureTexture(), tint, dx, dy, dw, dh,
               sx / texWidth, sy / texHeight, (sx + sw) / texWidth, (sy + sh) / texHeight);
    }
docs: Draws this image with the supplied transform, and source and target dimensions.