关于Form.Paint事件绘制缓慢问题

[pywepe]

先上代码:

 private void Screenshot() {

            Image myImg = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
            Graphics g = Graphics.FromImage(myImg);
            g.CopyFromScreen(new Point(0, 0), new Point(0, 0), Screen.PrimaryScreen.Bounds.Size);
            //SendKeys.Send("{PRTSC}"); 

            //Form form = new MyForm();
            Form form = new Form();
            form.FormBorderStyle = FormBorderStyle.None;
            form.BackgroundImage = myImg;  // 截取的图片作为Form的背景图片
            form.Size = new System.Drawing.Size(myImg.Size.Width, myImg.Size.Height);
            
            form.Paint += new PaintEventHandler(delegate(object sender,PaintEventArgs args){
               Graphics gg = args.Graphics;

               Image offsetScr = new Bitmap(args.ClipRectangle.Width, args.ClipRectangle.Height);
               Graphics srcG = Graphics.FromImage(offsetScr);

               Color c = Color.FromArgb(150, 0, 0, 0);
               Brush brush = new SolidBrush(c);
               srcG.FillRectangle(brush, args.ClipRectangle);
               brush.Dispose();
               srcG.Dispose();

               gg.DrawImage(offsetScr, args.ClipRectangle);
               offsetScr.Dispose();

               Console.WriteLine("OnPaint");
           });

            form.KeyDown += new KeyEventHandler(delegate(object sender, KeyEventArgs args)
            {
                if (args.KeyCode == Keys.Escape)
                {
                    form.Hide();
                    form.Dispose();
                }
                else if (args.KeyCode == Keys.S && args.Control) {
                    SaveFileDialog sd = new SaveFileDialog();
                    sd.InitialDirectory = ".";
                    sd.Filter = "PNG图片|*.png";
                    DialogResult r = sd.ShowDialog();
                    if (r == DialogResult.OK)
                    {
                        myImg.Save(sd.FileName, System.Drawing.Imaging.ImageFormat.Png);

                    }
                }
            });
            
            form.Show();

            /*
            Panel p = new Panel();
            p.Dock = DockStyle.Fill;
            p.BackColor = Color.FromArgb(150, 0, 0, 0);
            p.Paint += new PaintEventHandler(delegate(object sender,PaintEventArgs args){
                Console.WriteLine("on paint");
            });
            form.Controls.Add(p);
             */
                 
        }

主要是这一段代码:

form.Paint += new PaintEventHandler(delegate(object sender,PaintEventArgs args){
               Graphics gg = args.Graphics;
               // 这里有一个双缓冲,不用又缓冲效果也是一样的

               Image offsetScr = new Bitmap(args.ClipRectangle.Width, args.ClipRectangle.Height);
               Graphics srcG = Graphics.FromImage(offsetScr);

               Color c = Color.FromArgb(150, 0, 0, 0);
               Brush brush = new SolidBrush(c);
               srcG.FillRectangle(brush, args.ClipRectangle);
               brush.Dispose();
               srcG.Dispose();

               gg.DrawImage(offsetScr, args.ClipRectangle);
               offsetScr.Dispose();
  
               Console.WriteLine("OnPaint");
           });

截取的图片作为Form的背景图片,然后再在背景图片之上绘制一个半透明的矩形,以达到类似QQ截图的效果.

可是,当程序显示这个Form时,半透明的矩形是从上到下慢慢绘制的,并不是一次性完全显示.
上一个图说明这个过程:








可以确定的是这个Paint事件在Form显示的时候只触发了一次,因数只打印了一次OnPaint.
为什么矩形不是一次性绘制完成的呢?
怎么样才能达到一次性绘制完成的效果呢?

请大家不吝赐教

[bdmh]

你在什么时候触发的OnPaint事件，或许跟你的触发条件有关系，如果矩形是逐步形成的，那肯定会多次调用OnPaint，你看看ClipRectangle这个东西是怎样的

[足球中国]

java代码书写方式弄到c#里看着特别。
args.ClipRectangle.Width, args.ClipRectangle.Height 应该这个地方有问题。

[pywepe]

问题已得到解决,谢谢大家.
是没有双缓冲导致的,Form.DoubleBuffered = true 就没问题了

[gomoku]

private void Screenshot()
{
    new MyScreenCapturer().ShowDialog();
}
class MyScreenCapturer : Form
{
    Bitmap myImg = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
    public MyScreenCapturer() 
    { 
        using (Graphics g = Graphics.FromImage(myImg))
        {
            g.CopyFromScreen(Point.Empty, Point.Empty, Screen.PrimaryScreen.Bounds.Size);
        }
        this.FormBorderStyle = FormBorderStyle.None;
        this.Size = Screen.PrimaryScreen.Bounds.Size;
    }
    protected override void OnPaintBackground(PaintEventArgs e){/* do nothing */}
    protected override void OnPaint(PaintEventArgs e)
    {
        e.Graphics.DrawImageUnscaled(myImg, Point.Empty);
        using (Brush brush = new SolidBrush(Color.FromArgb(150, 0, 0, 0)))
        {
            Region mask = new Region(this.Bounds); mask.Exclude(this.GetSelection());
            e.Graphics.Clip = mask;
            e.Graphics.FillRectangle(brush, 0, 0, myImg.Width, myImg.Height);
        }
    }
    protected override void OnMouseDown(MouseEventArgs e)
    {
        this.mouseDown = this.mouseMove = e.Location;
    }
    protected override void OnMouseMove(MouseEventArgs e)
    {
        if (this.Capture)
        {
            Rectangle last = GetSelection();
            mouseMove = e.Location;
            this.Invalidate(Rectangle.Union(last, GetSelection()));
        }
    }
    protected override void OnMouseUp(MouseEventArgs e)
    {
        Rectangle rect = this.GetSelection();
        if (rect.Size != Size.Empty)
        {
            SaveFileDialog sd = new SaveFileDialog() {Filter = "PNG图片|*.png"};
            if (sd.ShowDialog() == DialogResult.OK)
            {
                myImg.Clone(rect, myImg.PixelFormat).Save(sd.FileName, System.Drawing.Imaging.ImageFormat.Png);
            }
            this.Close();
        }
    }
    private Rectangle GetSelection()
    {
        Point location = new Point(Math.Min(mouseDown.X, mouseMove.X), Math.Min(mouseDown.Y, mouseMove.Y));
        Size size = new Size(Math.Abs(mouseDown.X - mouseMove.X), Math.Abs(mouseDown.Y - mouseMove.Y));
        return new Rectangle(location, size);
    }
    Point mouseDown, mouseMove;
}

[orochiheart]

[Quote=引用 3 楼 的回复:]
问题已得到解决,谢谢大家.
是没有双缓冲导致的,Form.DoubleBuffered = true 就没问题了
[/Quote]
留个痕迹

[pywepe]

[Quote=引用 4 楼 的回复:]

C# code

private void Screenshot()
{
new MyScreenCapturer().ShowDialog();
}
class MyScreenCapturer : Form
{
Bitmap myImg = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.……
[/Quote]

同样有问题