C#中GDI+编程10个基本技巧二

5、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);

}

6、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.EventArgse)

{

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);

}

7、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。

下程序将原定点移动到控件中心，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);

8、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);

}

9、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);

}

10、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);

}

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