C#使用BufferedGraphics实现GDI-双缓冲绘图.doc

      使用双缓冲的图形可以减少或消除重绘显示图面时产生的闪烁。使用双缓冲时，更新的图形首先被绘制到内存的缓冲区中，然后，此缓冲区的内容被迅速写入某些或所有显示的图面中。显示图形的重写相对简短，这通常可以减少或消除有时在更新图形时出现的闪烁。

    使用C# GDI+绘图，实现双缓冲绘图有几种方法，在这篇文章中，将介绍其中的一种——使用BufferedGraphics实现GDI+双缓冲绘图。

    下面的代码示例演示如何使用 BufferedGraphics 对象绘制以下图形，这些图形使用几种类型的缓冲实现。单击窗体将启动或停止一个计时器，该计时器将引起绘制更新。绘制更新使您可以观察双缓冲的效果。右击窗体将循环使用下列绘制模式：
· 对于 Form，直接绘制到 Handle。
· 对使用 OptimizedDoubleBuffer 控件样式的 OnPaint 方法进行重写，以进行绘制
· 对于不使用 OptimizedDoubleBuffer 控件样式的窗体方法，重写 OnPaint 方法以进行绘制。
    在每种模式下都将绘制文本，以标识当前模式并描述按下每个鼠标按钮时发生的行为。
using System;

using System.ComponentModel;

using System.Drawing;

using System.Windows.Forms;

namespace BufferingExample

{

public class BufferingExample : Form

{

private BufferedGraphicsContext context;

private BufferedGraphics grafx;

private byte bufferingMode;

private string[] bufferingModeStrings =

{ "Draw to Form without OptimizedDoubleBufferring control style",

"Draw to Form using OptimizedDoubleBuffering control style",

"Draw to HDC for form" };

private System.Windows.Forms.Timer timer1;

private byte count;

public BufferingExample() : base()

{

// Configure the Form for this example.

this.Text = "User double buffering";

this.MouseDown += new MouseEventHandler(this.MouseDownHandler);

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

this.SetStyle( ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint, true );

// Configure a timer to draw graphics updates.

timer1 = new System.Windows.Forms.Timer();

timer1.Interval = 200;

timer1.Tick += new EventHandler(this.OnTimer);

bufferingMode = 2;

count = 0;

// Retrieves the BufferedGraphicsContext for the

// current application domain.

context = BufferedGraphicsManager.Current;

// 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);

}

private void MouseDownHandler(object sender, MouseEventArgs e)

{

if( e.Button == MouseButtons.Right )

{

// Cycle the buffering mode.

if( ++bufferingMode > 2 )

bufferingMode = 0;

// If the previous buffering mode used

// the OptimizedDoubleBuffering ControlStyle,

// disable the control style.

if( bufferingMode == 1 )

this.SetStyle( ControlStyles.OptimizedDoubleBuffer, true );

// If the current buffering mode uses

// the OptimizedDoubleBuffering ControlStyle,

// enabke the control style.

if( bufferingMode == 2 )

this.SetStyle( ControlStyles.OptimizedDoubleBuffer, false );

// Cause the background to be cleared and redraw.

count = 6;

DrawToBuffer(grafx.Graphics);

this.Refresh();

}

else

{

// Toggle whether the redraw timer is active.

if( timer1.Enabled )

timer1.Stop();

else

timer1.Start();

}

}

private void OnTimer(object sender, EventArgs e)

{

// Draw randomly positioned ellipses to the buffer.

DrawToBuffer(grafx.Graphics);

// If in bufferingMode 2, draw to the form's HDC.

if( bufferingMode == 2 )

// Render the graphics buffer to the form's HDC.

grafx.Render(Graphics.FromHwnd(this.Handle));

// If in bufferingMode 0 or 1, draw in the paint method.

else

this.Refresh();

}

private void OnResize(object sender, EventArgs e)

{

// Re-create the graphics buffer for a new window size.

context.MaximumBuffer = new Size(this.Width+1, this.Height+1);

if( grafx != null )

{

grafx.Dispose();

grafx = null;

}

grafx = context.Allocate(this.CreateGraphics(),

new Rectangle( 0, 0, this.Width, this.Height ));

// Cause the background to be cleared and redraw.

count = 6;

DrawToBuffer(grafx.Graphics);

this.Refresh();

}

private void DrawToBuffer(Graphics g)

{

// Clear the graphics buffer every five updates.

if( ++count > 5 )

{

count = 0;

grafx.Graphics.FillRectangle(Brushes.Black, 0, 0, this.Width, this.Height);

}

// Draw randomly positioned and colored ellipses.

Random rnd = new Random();

for( int i=0; i<20; i++ )

{

int px = rnd.Next(20,this.Width-40);

int py = rnd.Next(20,this.Height-40);

g.DrawEllipse(new Pen(Color.FromArgb(rnd.Next(0, 255), rnd.Next(0,255), rnd.Next(0,255)), 1),

px, py, px+rnd.Next(0 this.Width-px-20), py+rnd.Next(0, this.Height-py-20));

}

// Draw information strings.

g.DrawString("Buffering Mode: "+bufferingModeStrings[bufferingMode], new Font("Arial", 8), Brushes.White, 10, 10);

g.DrawString("Right-click to cycle buffering mode", new Font("Arial", 8), Brushes.White, 10, 22);

g.DrawString("Left-click to toggle timed display refresh", new Font("Arial", 8), Brushes.White, 10, 34);

}

protected override void OnPaint(PaintEventArgs e)

{

grafx.Render(e.Graphics);

}

[STAThread]

public static void Main(string[] args)

{

Application.Run(new BufferingExample());

}

}

}