Im doing a Game in Xaml WPF, I didn't really choose the tools and languages. It's to be hidden in a really big app with a lot of codes.

The whole snake take place in a simple xaml canvas and xaml.cs file here

https://github.com/Jebik/XAMLSnake/blob/master/XAMLSnake/XAMLSnake/XAMLSnakeWindow.xaml.cs

But.. Actually the snake became really laggy after being taller than 20 part. And even before the speed is absolutly not constant.

I don't know a lot about game programation i'm doing software for a while now.

How can i improve this game? Make speed less dependend to snake size? Make it lagging way less with same computer perf?

First post on code Review feel free to comment if i must change the topic message ..

I think the more important is paintSnake Method called every timer Tick

 private void paintSnake(Point currentposition)
        {
            cleanSnake();
            paintSnakeHead(currentposition);
            paintSnakeBody(currentposition);
        }
        private void cleanSnake()
        {
            var count = paintCanvas.Children.Count;
            var toDel = count - (NbBonus + 1);
            paintCanvas.Children.RemoveRange(NbBonus + 1, toDel);
        }
        private void paintSnakeHead(Point currentposition)
        {
            var rot = GetRotation();
            RotateTransform aRotateTransform = new RotateTransform();
            aRotateTransform.CenterX = 0.5;
            aRotateTransform.CenterY = 0.5;
            aRotateTransform.Angle = rot;
            _headBrush.RelativeTransform = aRotateTransform;
            Rectangle headRect = new Rectangle();
            headRect.Fill = _headBrush;
            headRect.Height = headSize;
            headRect.Width = headSize;
            Canvas.SetTop(headRect, currentposition.Y);
            Canvas.SetLeft(headRect, currentposition.X);
            //On decale tout les point du snake
            snakePoints.Insert(0, currentposition);
            paintCanvas.Children.Add(headRect);
            int count = snakePoints.Count;
            // Restrict the tail of the snake
            if (count > length)
            {
                snakePoints.RemoveAt(length);
            }
        }
        private int GetRotation()
        {
            switch (direction)
            {
                case (int)MOVINGDIRECTION.DOWNWARDS:
                    return 180;
                case (int)MOVINGDIRECTION.UPWARDS:
                    return 0;
                case (int)MOVINGDIRECTION.TOLEFT:
                    return 270;
                case (int)MOVINGDIRECTION.TORIGHT:
                    return 90;
                default:
                    return 0;
            }
        }
        private void paintSnakeBody(Point currentposition)
        {
            for (int i = 1; i < snakePoints.Count; i++)
            {
                //On ne dessinne un cercle que tout les headsize position
                if (i % headSize == 0)
                {
                    Rectangle bodyRect = new Rectangle();
                    bodyRect.Fill = _bodyBrush;
                    bodyRect.Height = headSize;
                    bodyRect.Width = headSize;
                    Canvas.SetTop(bodyRect, snakePoints[i].Y);
                    Canvas.SetLeft(bodyRect, snakePoints[i].X);
                    paintCanvas.Children.Add(bodyRect);
                }
            }
        }