C# 双缓冲有负面影响

Question

我编写了下面的简单程序，每 100 毫秒在屏幕上画一条线（由计时器 1 触发）。我注意到绘图有点闪烁（也就是说，窗口并不总是完全蓝色，而是透出一些灰色）。所以我的想法是使用双缓冲。但当我这样做时，事情变得更糟了。现在屏幕几乎总是灰色的，只有偶尔出现蓝色（由timer2 演示，每 2000 毫秒切换一次 DoubleBuffered 属性）。

对此有何解释？

using System;
using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApplication1 {
    public partial class Form1 : Form {
        public Form1() {
            InitializeComponent();
        }

        private void Form1_Paint(object sender, PaintEventArgs e) {
            Graphics g = CreateGraphics();
            Pen pen = new Pen(Color.Blue, 1.0f);
            Random rnd = new Random();
            for (int i = 0; i < Height; i++)
                g.DrawLine(pen, 0, i, Width, i);
        }

        // every 100 ms
        private void timer1_Tick(object sender, EventArgs e) {
            Invalidate();
        }

        // every 2000 ms
        private void timer2_Tick(object sender, EventArgs e) {
            DoubleBuffered = !DoubleBuffered;
            this.Text = DoubleBuffered ? "yes" : "no";
        }
    }
}

Answer 1

我会将所有项目绘制到您自己的缓冲区中，然后立即将其全部复制进去。我在许多应用程序中将其用于图形，并且它对我来说一直非常有效：

    public Form1()
    {
        InitializeComponent();
    }
    private void timer1_Tick(object sender, EventArgs e)
    {
        Invalidate();// every 100 ms
    }
    private void Form1_Load(object sender, EventArgs e)
    {
        DoubleBuffered = true;
    }
    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        Bitmap buffer = new Bitmap(Width, Height);
        Graphics g = Graphics.FromImage(buffer);
        Pen pen = new Pen(Color.Blue, 1.0f);
        //Random rnd = new Random();
        for (int i = 0; i < Height; i++)
            g.DrawLine(pen, 0, i, Width, i);
        BackgroundImage = buffer;
    }

编辑：经过进一步调查，看来您的问题在于您将 Graphics 对象设置为：

Graphics g = CreateGraphics();

需要是：

Graphics g = e.Graphics();

所以你的问题可以通过像我上面那样创建一个手动缓冲区，或者简单地改变你的 Graphics 对象来解决。我已经测试了两者并且它们都有效。

Answer 2

无需使用多个缓冲区或位图对象或任何东西。

为什么不使用Paint事件提供的Graphics对象呢？像这样：

private void Form1_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;
    Pen pen = new Pen(Color.Blue, 1.0f);
    Random rnd = new Random();
    for (int i = 0; i < Height; i++)
        g.DrawLine(pen, 0, i, Width, i);
}

Answer 3

测试时，尝试在构造函数中将双缓冲属性设置为 true 一次。

您需要利用后台缓冲区。试试这个：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace DoubleBufferTest
{
    public partial class Form1 : Form
    {
        private BufferedGraphicsContext context;
        private BufferedGraphics grafx;

        public Form1()
        {
            InitializeComponent();

            this.Resize += new EventHandler(this.OnResize);
            DoubleBuffered = true;

            // Retrieves the BufferedGraphicsContext for the 
            // current application domain.
            context = BufferedGraphicsManager.Current;

            UpdateBuffer();
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            this.Refresh();

        }

        private void OnResize(object sender, EventArgs e)
        {
            UpdateBuffer();
            this.Refresh();
        }

        private void UpdateBuffer()
        {
            // Sets the maximum size for the primary graphics buffer
            // of the buffered graphics context for the application
            // domain.  Any allocation requests for a buffer larger 
            // than this will create a temporary buffered graphics 
            // context to host the graphics buffer.
            context.MaximumBuffer = new Size(this.Width + 1, this.Height + 1);

            // Allocates a graphics buffer the size of this form
            // using the pixel format of the Graphics created by 
            // the Form.CreateGraphics() method, which returns a 
            // Graphics object that matches the pixel format of the form.
            grafx = context.Allocate(this.CreateGraphics(),
                 new Rectangle(0, 0, this.Width, this.Height));

            // Draw the first frame to the buffer.
            DrawToBuffer(grafx.Graphics);
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            grafx.Render(e.Graphics);
        }

        private void DrawToBuffer(Graphics g)
        {
            //Graphics g = grafx.Graphics;
            Pen pen = new Pen(Color.Blue, 1.0f);
            //Random rnd = new Random();
            for (int i = 0; i < Height; i++)
                g.DrawLine(pen, 0, i, Width, i);
        }
    }
}

这是一个稍微修改过的版本 双缓冲示例在 MSDN 上。