gpuDrawLayer1.swift

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    guard let newTouchPoint = touches.first?.location(in: self) else { return }

    let lastTouchPoint: CGPoint = line.last ?? .zero
    line.append(newTouchPoint)
    let rect = calculateRectBetween(lastPoint: lastTouchPoint, newPoint: newTouchPoint)
    layer.setNeedsDisplay(rect)
}