docs: public static RenderTarget create (Graphics gfx, final Texture tex) {
      GL20 gl = gfx.gl;
      final int fb = gl.glGenFramebuffer();
      if (fb == 0) throw new RuntimeException("Failed to gen framebuffer: " + gl.glGetError());
      gl.glBindFramebuffer(GL_FRAMEBUFFER, fb);
      gl.glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex.id, 0);
      gl.checkError("RenderTarget.create");
      return new RenderTarget (gfx) {
        public int id () { return fb; }
        public int width () { return tex.pixelWidth; }
        public int height () { return tex.pixelHeight; }
        public float xscale () { return tex.pixelWidth / tex.displayWidth; }
        public float yscale () { return tex.pixelHeight / tex.displayHeight; }
        public boolean flip () { return false; }
      };
    }