GDI+编程的10个基本技巧（转）

创建绘图表面 

创建绘图表面有两种常用的方法。下面设法得到PictureBox的绘图表面。 

private void Form1_Load(object sender, System.EventArgs e) 
{ 
//得到pictureBox1的绘图表面 
Graphics g = this.pictureBox1.CreateGraphics(); 
} 

private void pictureBox1_Paint(object sender, System.Windows.Forms.PaintEventArgs e) 
{ 
//得到pictureBox1的绘图表面 
Graphics g = e.Graphics; 
} 

可以利用Graphics对象绘制出各种图形图案。控件的Paint事件和OnPaint方法都可以绘图都是好时机。
在OnPaint方法里绘制图案一定从参数e里面得到Graphics属性。下面是两个例子。 
protected override void OnPaint(PaintEventArgs e) 
{ 
e.Graphics.Clear(Color.White); 
float x, y, w, h; 
x = this.Left+2; 
y = this.Top+2; 
w = this.Width-4; 
h = this.Height-4; 
Pen pen = new Pen(Color.Red, 2); 
e.Graphics.DrawRectangle(pen, x, y, w, h); 
base.OnPaint (e); 
} 

private void PictureBoxII_Resize(object sender, EventArgs e) 
{ 
this.Invalidate(); 
} 

private void button1_Click(object sender, System.EventArgs e) 
{ 
this.pictureBoxII1.CreateGraphics().FillEllipse( 
Brushes.Blue, 10, 20, 50, 100); 
} 

和文本有关的三个类： 
FontFamily——定义有着相似的基本设计但在形式上有某些差异的一组字样。无法继承此类。 
Font——定义特定的文本格式，包括字体、字号和字形属性。无法继承此类。 
StringFormat——封装文本布局信息（如对齐方式和行距），显示操作（如省略号插入和国家标准 (National) 数字位替换）和 OpenType 功能。无法继承此类。 
下面的程序显示了一段文字。 

private void button2_Click(object sender, System.EventArgs e) 
{ 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
g.FillRectangle(Brushes.White, this.pictureBoxII1.ClientRectangle); 

string s = "aaaaaaaaaaaaaaaaaaaaaaaaaa"; 
FontFamily fm = new FontFamily("ËÎÌå"); 
Font f = new Font(fm, 20, FontStyle.Bold, GraphicsUnit.Point); 
RectangleF rectF = new RectangleF(30, 20, 180, 205); 
StringFormat sf = new StringFormat(); 
SolidBrush sbrush = new SolidBrush(Color.FromArgb(255, 0, 0, 255)); 
sf.LineAlignment = StringAlignment.Center; 
sf.FormatFlags = StringFormatFlags.DirectionVertical; 
g.DrawString(s, f, sbrush, rectF, sf); 
} 

GDI+的路径——GraphicsPath类 

GraphicsPath类提供了一系列属性和方法，利用它可以获取路径上的关键点，可以添加直线段、圆等几何元素。可以获得包围矩形，进行拾取测试。这些功能都怎么用，要仔细看一下。 

private void button3_Click(object sender, System.EventArgs e) 
{ 
//绘图表面 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
//填充成白色 
g.FillRectangle(Brushes.White, this.ClientRectangle); 
//弄一个绘图路径¶ 
GraphicsPath gp = new GraphicsPath(); 
//添加一些集合图形 
gp.AddEllipse(20, 20, 300, 200); 
gp.AddPie(50, 100, 300, 100, 45, 200); 
gp.AddRectangle(new Rectangle(100, 30, 100, 80)); 
//在绘图表面上绘制绘图路径 
g.DrawPath(Pens.Blue, gp); 
//平移 
g.TranslateTransform(200, 20); 

//填充绘图路径¶ 
g.FillPath(Brushes.GreenYellow, gp); 
gp.Dispose(); 
} 

区域——Region类 

从已有的矩形和路径可以创建Region。使用Graphics.FillRegion方法绘制Region。该类指示由矩形和由路径构成的图形形状的内部。无法继承此类。 
渐变色填充 

需要使用两个刷子： 
线性梯度刷子(LinearGradientBrush) 
路径梯度刷子(PathGuadientBrush) 

private void button4_Click(object sender, System.EventArgs e) 
{
//绘图表面 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
g.FillRectangle(Brushes.White, this.pictureBoxII1.ClientRectangle); 

//定义一个线性梯度刷子 

LinearGradientBrush lgbrush = 
new LinearGradientBrush( 
new Point(0, 10), 
new Point(150, 10), 
Color.FromArgb(255, 0, 0), 
Color.FromArgb(0, 255, 0)); 
Pen pen = new Pen(lgbrush); 

//用线性笔刷梯度效果的笔绘制一条直线段并填充一个矩形 

g.DrawLine(pen, 10, 130, 500, 130); 
g.FillRectangle(lgbrush, 10, 150, 370, 30); 

//定义路径并添加一个椭圆 
GraphicsPath gp = new GraphicsPath(); 
gp.AddEllipse(10, 10, 200, 100); 

//用该路径定义路径梯度刷子 
PathGradientBrush brush = 
new PathGradientBrush(gp); 

//颜色数组 
Color[] colors = { 
Color.FromArgb(255, 0, 0), 
Color.FromArgb(100, 100, 100), 
Color.FromArgb(0, 255, 0), 
Color.FromArgb(0, 0, 255)}; 

//定义颜色渐变比率 
float[] r = {0.0f, 0.3f, 0.6f, 1.0f}; 
ColorBlend blend = new ColorBlend(); 
blend.Colors = colors; 
blend.Positions = r; 
brush.InterpolationColors = blend; 

//在椭圆外填充一个矩形 
g.FillRectangle(brush, 0, 0, 210, 110); 

//用添加了椭圆的路径定义第二个路径梯度刷子 
GraphicsPath gp2 = new GraphicsPath(); 
gp2.AddEllipse(300, 0, 200, 100); 
PathGradientBrush brush2 = new PathGradientBrush(gp2); 

//设置中心点位置和颜色 
brush2.CenterPoint = new PointF(450, 50); 
brush2.CenterColor = Color.FromArgb(0, 255, 0); 

//设置边界颜色 
Color[] color2 = {Color.FromArgb(255, 0, 0)}; 
brush2.SurroundColors = color2; 

//用第二个梯度刷填充椭圆 
g.FillEllipse(brush2, 300, 0, 200, 100); 
}

GDI+的坐标系统
通用坐标系——用户自定义坐标系。
页面坐标系——虚拟坐标系。
设备坐标系——屏幕坐标系。
当页面坐标系和设备坐标系的单位都是象素时，它们相同。

private void button10_Click(object sender, System.EventArgs e) 
{ 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
g.Clear(Color.White); 
this.Draw(g); 
} 
private void Draw(Graphics g) 
{ 
g.DrawLine(Pens.Black, 10, 10, 100, 100); 
g.DrawEllipse(Pens.Black, 50, 50, 200, 100); 
g.DrawArc(Pens.Black, 100, 10, 100, 100, 20, 160); 
g.DrawRectangle(Pens.Green, 50, 200, 150, 100); 
}

private void button5_Click(object sender, System.EventArgs e) 
{
//左移 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
g.Clear(Color.White); 
g.TranslateTransform(-50, 0); 
this.Draw(g); 
} 

private void button6_Click(object sender, System.EventArgs e) 
{ 
//右移 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
g.Clear(Color.White); 
g.TranslateTransform(50, 0); 
this.Draw(g); 
} 

private void button7_Click(object sender, System.EventArgs e) 
{ 
//旋转 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
g.Clear(Color.White); 
g.RotateTransform(-30); 
this.Draw(g); 
} 

private void button8_Click(object sender, System.EventArgs e) 
{ 
//放大 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
g.Clear(Color.White); 
g.ScaleTransform(1.2f, 1.2f); 
this.Draw(g); 
} 

private void button9_Click(object sender, System.EventArgs e) 
{ 
//缩小 
Graphics g = this.pictureBoxII1.CreateGraphics(); 
g.Clear(Color.White); 
g.ScaleTransform(0.8f, 0.8f); 
this.Draw(g); 
} 

全局坐标——变换对于绘图表面上的每个图元都会产生影响。通常用于设定通用坐标系。

一下程序将原定移动到控件中心，并且Y轴正向朝上。

//先画一个圆 

Graphics g = e.Graphics; 
g.FillRectangle(Brushes.White, this.ClientRectangle); 
g.DrawEllipse(Pens.Black, -100, -100, 200, 200); 

//使y轴正向朝上，必须做相对于x轴镜像 
//变换矩阵为[1,0,0,-1,0,0] 
Matrix mat = new Matrix(1, 0, 0, -1, 0, 0); 
g.Transform = mat; 
Rectangle rect = this.ClientRectangle; 
int w = rect.Width; 
int h = rect.Height; 
g.TranslateTransform(w/2, -h/2);

//以原点为中心，做一个半径为100的圆 
g.DrawEllipse(Pens.Red, -100, -100, 200, 200); 
g.TranslateTransform(100, 100); 
g.DrawEllipse(Pens.Green, -100, -100, 200, 200); 
g.ScaleTransform(2, 2); 
g.DrawEllipse(Pens.Blue, -100, -100, 200, 200); 

局部坐标系——只对某些图形进行变换，而其它图形元素不变。

protected override void OnPaint(PaintEventArgs e) 
{ 
Graphics g = e.Graphics; 
//客户区设置为白色 
g.FillRectangle(Brushes.White, this.ClientRectangle); 

//y轴朝上 
Matrix mat = new Matrix(1, 0, 0, -1, 0, 0); 
g.Transform = mat; 

//移动坐标原点到窗体中心 
Rectangle rect = this.ClientRectangle; 
int w = rect.Width; 
int h = rect.Height; 
g.TranslateTransform(w/2, -h/2);

 
//在全局坐标下绘制椭圆 
g.DrawEllipse(Pens.Red, -100, -100, 200, 200); 
g.FillRectangle(Brushes.Black, -108, 0, 8, 8); 
g.FillRectangle(Brushes.Black, 100, 0, 8, 8); 
g.FillRectangle(Brushes.Black, 0, 100, 8, 8); 
g.FillRectangle(Brushes.Black, 0, -108, 8, 8); 

//创建一个椭圆然后在局部坐标系中进行变换 
GraphicsPath gp = new GraphicsPath(); 
gp.AddEllipse(-100, -100, 200, 200); 
Matrix mat2 = new Matrix(); 

//平移 
mat2.Translate(150, 150); 

//旋转 
mat2.Rotate(30); 
gp.Transform(mat2); 
g.DrawPath(Pens.Blue, gp); 
PointF[] p = gp.PathPoints; 
g.FillRectangle(Brushes.Black, p[0].X-2, p[0].Y+2, 4, 4); 
g.FillRectangle(Brushes.Black, p[3].X-2, p[3].Y+2, 4, 4); 
g.FillRectangle(Brushes.Black, p[6].X-4, p[6].Y-4, 4, 4); 
g.FillRectangle(Brushes.Black, p[9].X-4, p[9].Y-4, 4, 4); 
gp.Dispose(); 
//base.OnPaint (e); 
}

Alpha混合

Color.FromArgb()的A就是Alpha。Alpha的取值范围从0到255。0表示完全透明，255完全不透明。

当前色＝前景色×alpha/255+背景色×（255－alpha）/255

protected override void OnPaint(PaintEventArgs e) 
{ 
Graphics g = e.Graphics; 
//创建一个填充矩形 
SolidBrush brush = new SolidBrush(Color.BlueViolet); 
g.FillRectangle(brush, 180, 70, 200, 150); 

//创建一个位图，其中两个位图之间有透明效果 
Bitmap bm1 = new Bitmap(200, 100); 
Graphics bg1 = Graphics.FromImage(bm1); 
SolidBrush redBrush = new SolidBrush(Color.FromArgb(210, 255, 0, 0)); 
SolidBrush greenBrush = new SolidBrush(Color.FromArgb(210, 0, 255, 0)); 
bg1.FillRectangle(redBrush, 0, 0, 150, 70); 
bg1.FillRectangle(greenBrush, 30, 30, 150, 70); 
g.DrawImage(bm1, 100, 100); 

//创建一个位图，其中两个位图之间没有透明效果 
Bitmap bm2 = new Bitmap(200, 100); 
Graphics bg2 = Graphics.FromImage(bm2); 
bg2.CompositingMode = CompositingMode.SourceCopy; 
bg2.FillRectangle(redBrush, 0, 0, 150, 170); 
bg2.FillRectangle(greenBrush, 30, 30, 150, 70); 
g.CompositingQuality = CompositingQuality.GammaCorrected; 
g.DrawImage(bm2, 300, 200); 
//base.OnPaint (e); 
} 

反走样

protected override void OnPaint(PaintEventArgs e) 
{ 
Graphics g = e.Graphics; 
//放大8倍 
g.ScaleTransform(8, 8); 
//没有反走样的图形和文字 
Draw(g); 
//设置反走样 
g.SmoothingMode = SmoothingMode.AntiAlias; 
//右移40 
g.TranslateTransform(40, 0); 
//再绘制就是反走样之后的了 
Draw(g); 
//base.OnPaint (e); 
} 
private void Draw(Graphics g) 
{ 
//绘制图形和文字 
g.DrawLine(Pens.Gray, 10, 10, 40, 20); 
g.DrawEllipse(Pens.Gray, 20, 20, 30, 10); 
string s = "反走样测试";
Font font = new Font("宋体", 5); 
SolidBrush brush = new SolidBrush(Color.Gray); 
g.DrawString(s, font, brush, 10, 40); 
}