function cleanViewport(uniformState) {
  if (uniformState._viewportDirty) {
    const v = uniformState._viewport;
    Matrix4.computeOrthographicOffCenter(
      v.x,
      v.x + v.width,
      v.y,
      v.y + v.height,
      0.0,
      1.0,
      uniformState._viewportOrthographicMatrix,
    );
    Matrix4.computeViewportTransformation(
      v,
      0.0,
      1.0,
      uniformState._viewportTransformation,
    );
    uniformState._viewportDirty = false;
  }
}
Synchronizes frame state with the uniform state.  This is called
by the {@link Scene} when rendering to ensure that automatic GLSL uniforms
are set to the right value.

@param {FrameState} frameState The frameState to synchronize with.