C#使用BufferedGraphics实现GDI+双缓冲绘图 转
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 DoubleBufferShown
{
public partial 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);
}
}
}