C#中GDI+編程10個基本技巧二

5、漸層色填充

需要使用兩個刷子：

線性梯度刷子(LinearGradientBrush)

路徑梯度刷子(PathGuadientBrush)

private void button4_Click(object sender,System.EventArgs e)

{

//繪圖表面

Graphics g =this.pictureBoxII1.CreateGraphics();

g.FillRectangle(Brushes.White,this.pictureBoxII1.ClientRectangle);

//定義一個線性梯度刷子

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);

//用線性筆刷梯度效果的筆繪製一條直線段並填充一個矩形

g.DrawLine(pen, 10, 130, 500, 130);

g.FillRectangle(lgbrush, 10, 150, 370, 30);

//定義路徑並添加一個橢圓

GraphicsPath gp = new GraphicsPath();

gp.AddEllipse(10, 10, 200, 100);

//用該路徑定義路徑梯度刷子

PathGradientBrush brush =

new PathGradientBrush(gp);

//顏色數組

Color[] colors = {

Color.FromArgb(255, 0, 0),

Color.FromArgb(100, 100, 100),

Color.FromArgb(0, 255, 0),

Color.FromArgb(0, 0, 255)};

//定義色彩坡形比率

float[] r = {0.0f, 0.3f, 0.6f, 1.0f};

ColorBlend blend = new ColorBlend();

blend.Colors = colors;

blend.Positions = r;

brush.InterpolationColors = blend;

//在橢圓外填充一個矩形

g.FillRectangle(brush, 0, 0, 210, 110);

//用添加了橢圓的路徑定義第二個路徑梯度刷子

GraphicsPath gp2 = new GraphicsPath();

gp2.AddEllipse(300, 0, 200, 100);

PathGradientBrush brush2 = new PathGradientBrush(gp2);

//設定中心點位置和顏色

brush2.CenterPoint = new PointF(450, 50);

brush2.CenterColor = Color.FromArgb(0, 255, 0);

//設定邊界顏色

Color[] color2 = {Color.FromArgb(255, 0, 0)};

brush2.SurroundColors = color2;

//用第二個梯度刷填充橢圓

g.FillEllipse(brush2, 300, 0, 200, 100);

}

6、GDI+的座標系統

通用座標系——使用者自訂座標系。

頁面座標系——虛擬座標系。
裝置座標系——螢幕座標系。

當頁面座標系和裝置座標系的單位都是象素時，它們相同。

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)

{

//旋轉

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)

{

//縮小

Graphics g = this.pictureBoxII1.CreateGraphics();

g.Clear(Color.White);

g.ScaleTransform(0.8f, 0.8f);

this.Draw(g);

}

7、全域座標——變換對於繪圖表面上的每個圖元都會產生影響。通常用於設定通用座標系。

下程式將原定點移動到控制項中心，並且Y軸正向朝上。

//先畫一個圓

Graphics g = e.Graphics;

g.FillRectangle(Brushes.White, this.ClientRectangle);

g.DrawEllipse(Pens.Black, -100, -100, 200, 200);

//使y軸正向朝上，必須做相對於x軸鏡像

//變換矩陣為[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);

//以原點為中心，做一個半徑為100的圓

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、局部座標系——只對某些圖形進行變換，而其它圖形元素不變。

protected override void OnPaint(PaintEventArgs e)

{

Graphics g = e.Graphics;

//客戶區設定為白色

g.FillRectangle(Brushes.White, this.ClientRectangle);

//y軸朝上

Matrix mat = new Matrix(1, 0, 0, -1, 0, 0);

g.Transform = mat;

//移動座標原點到表單中心

Rectangle rect = this.ClientRectangle;

int w = rect.Width;

int h = rect.Height;

g.TranslateTransform(w/2, -h/2);

//在全域座標下繪製橢圓

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);

//建立一個橢圓然後在局部座標系中進行變換

GraphicsPath gp = new GraphicsPath();

gp.AddEllipse(-100, -100, 200, 200);

Matrix mat2 = new Matrix();

//平移

mat2.Translate(150, 150);

//旋轉

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的取值範圍從0到255。0表示完全透明，255完全不透明。

當前色＝前景色彩×alpha/255+背景色×（255－alpha）/255

protected override void OnPaint(PaintEventArgs e)

{

Graphics g = e.Graphics;

//建立一個填充矩形

SolidBrush brush = new SolidBrush(Color.BlueViolet);

g.FillRectangle(brush, 180, 70, 200, 150);

//建立一個位元影像，其中兩個位元影像之間有透明效果

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);

//建立一個位元影像，其中兩個位元影像之間沒有透明效果

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、反走樣

protected override void OnPaint(PaintEventArgs e)

{

Graphics g = e.Graphics;

//放大8倍

g.ScaleTransform(8, 8);

//沒有反走樣的圖形和文字

Draw(g);

//設定反走樣

g.SmoothingMode = SmoothingMode.AntiAlias;

//右移40

g.TranslateTransform(40, 0);

//再繪製就是反走樣之後的了

Draw(g);
//base.OnPaint (e);

}
private void Draw(Graphics g)

{

//繪製圖形和文字

g.DrawLine(Pens.Gray, 10, 10, 40, 20);

g.DrawEllipse(Pens.Gray, 20, 20, 30, 10);

string s = "反走樣測試";

Font font = new Font("宋體", 5);

SolidBrush brush = new SolidBrush(Color.Gray);

g.DrawString(s, font, brush, 10, 40);

}