为什么渲染车削黑色

Question

我正在使用眼动仪在窗体上显示眼球运动。这些动作一直闪烁很多，所以我发现我可以使用BufferedGraphics，除了眼动开始之外，它们都可以正常工作，它将窗体从原始颜色变成黑色。这是代码。希望有人能帮助！

private void button2_Click(object sender, EventArgs e) 
{ 
    var host = new Host(); 
    var gazeStream = host.Streams.CreateGazePointDataStream(); 
    gazeStream.GazePoint((x, y, ts) 
     => drawCircle(new PointF((float)x, (float)y))); 
} 

delegate void SetCallback(PointF point); 

private void drawCircle(PointF point) 
{ 
    float x = point.X; 
    float y = point.Y; 

    if (this.InvokeRequired) 
    { 
     SetCallback d = new SetCallback(drawCircle); 
     this.Invoke(d, new object[] { point }); 
    } 
    else 
    { 
     SolidBrush semiTransBrush = new SolidBrush(Color.Coral); 
     Pen pen = new Pen(Color.Aquamarine, 2); 

     BufferedGraphicsContext currentContext; 
     BufferedGraphics myBuffer; 
     // Gets a reference to the current BufferedGraphicsContext 
     currentContext = BufferedGraphicsManager.Current; 
     // Creates a BufferedGraphics instance associated with Form1, and with 
     // dimensions the same size as the drawing surface of Form1. 
     myBuffer = currentContext.Allocate(this.CreateGraphics(),this.DisplayRectangle); 
     myBuffer.Graphics.DrawEllipse(pen, x, y, 100, 100); 
     myBuffer.Graphics.FillEllipse(semiTransBrush, x, y, 100, 100); 


     // Renders the contents of the buffer to the specified drawing surface. 
     myBuffer.Render(this.CreateGraphics()); 

     myBuffer.Dispose(); 
    } 

您可以在图片中看到的圆圈显示控件后面这似乎是形式没有了吗？

Answer 1

当您分配缓冲区时，它会使用您提供的图形创建兼容的渲染表面。但它不会复制它或任何东西，所以如果你只画一个圆圈，其余部分仍然是黑色的。

BufferedGraphics真的可以帮助您避免在特殊情况下闪烁（例如，系统双缓冲由于某种原因必须被禁用），但这里这是一个矫枉过正。

所以关键只是启用双缓冲，并在Paint事件（或OnPaint方法）中执行每个绘制。在你的代码中，你会立即进行绘制，它总是闪烁。相反，您应该使表单失效，并让系统执行定期重绘会话，如果您愿意，可以使用双重缓冲。

到构造函数：

SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.DoubleBuffer | ControlStyles.AllPaintingInWmPaint, true); 

然后修改Click事件：

private PointF lastGazePoint; 

private void button2_Click(object sender, EventArgs e) 
{ 
    var host = new Host(); 
    var gazeStream = host.Streams.CreateGazePointDataStream(); 
    gazeStream.GazePoint((x, y, ts) => 
     { 
      lastGazePoint = new PointF((float)x, (float)y); 
      Invalidate(); 
     }); 
} 

绘画本身：

protected override void OnPaint(PaintEventArgs e) 
{ 
    base.OnPaint(e); 
    DrawCircle(e.Graphics, lastGazePoint.X, lastGazePoint.Y); 
} 

最后，修改DrawCircle使用来自PaintEventArgs的Graphics ：

private void DrawCircle(Graphics g, float x, float y) 
{ 
    using (Brush semiTransBrush = new SolidBrush(Color.Coral)) 
    { 
     using (Pen pen = new Pen(Color.Aquamarine, 2)) 
     { 
      g.DrawEllipse(pen, x, y, 100, 100); 
      g.FillEllipse(semiTransBrush, x, y, 100, 100); 
     }   
    }   
}