GDI+編程10個基本技巧

創建繪圖表面

創建繪圖表面有兩種常用的方法。下面設法得到PictureBox的繪圖表面。
private void Form1_Load(object sender, System.EventArgs e)
{
//得到pictureBox1的繪圖表面
Graphics g = this.pictureBox1.CreateGraphics();
}

private void pictureBox1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
//得到pictureBox1的繪圖表面

Graphics g = e.Graphics;

}

可以利用Graphics對象繪製出各種圖形圖案。控件的Paint事件和OnPaint方法都可以繪圖都是好時機。在OnPaint方法裏繪製圖案一定從參數e裏面得到Graphics屬性。下面是兩個例子。

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);
}

和文本有關的三個類：
FontFamily——定義有着相似的基本設計但在形式上有某些差異的一組字樣。無法繼承此類。

Font——定義特定的文本格式，包括字體、字號和字形屬性。無法繼承此類。

StringFormat——封裝文本佈局信息（如對齊方式和行距），顯示操作（如省略號插入和國家標準 (National) 數字位替換）和 OpenType 功能。無法繼承此類。

下面的程序顯示了一段文字。
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+的路徑——GraphicsPath類

GraphicsPath類提供了一系列屬性和方法，利用它可以獲取路徑上的關鍵點，可以添加直線段、圓等幾何元素。可以獲得包圍矩形，進行拾取測試。這些功能都怎麼用，要仔細看一下。

private void button3_Click(object sender, System.EventArgs e)
{
//繪圖表面

Graphics g = this.pictureBoxII1.CreateGraphics();

//填充成白色

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

//弄一個繪圖路徑¶

GraphicsPath gp = new GraphicsPath();

//添加一些集合圖形

gp.AddEllipse(20, 20, 300, 200);

gp.AddPie(50, 100, 300, 100, 45, 200);

gp.AddRectangle(new Rectangle(100, 30, 100, 80));

//在繪圖表面上繪製繪圖路徑

g.DrawPath(Pens.Blue, gp);

//平移

g.TranslateTransform(200, 20);

//填充繪圖路徑¶

g.FillPath(Brushes.GreenYellow, gp);

gp.Dispose();
}

區域——Region類

從已有的矩形和路徑可以創建Region。使用Graphics.FillRegion方法繪製Region。該類指示由矩形和由路徑構成的圖形形狀的內部。無法繼承此類。

漸變色填充

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)};

//定義顏色漸變比率

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);

//設置中心點位置和顏色

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

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

//設置邊界顏色

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);

}

GDI+的座標系統

通用座標系——用戶自定義座標系。

頁面座標系——虛擬座標系。

設備座標系——屏幕座標系。

當頁面座標系和設備座標系的單位都是象素時，它們相同。

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);

}

全局座標——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。

一下程序將原定移動到控件中心，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

//變換矩陣爲[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);

//以原點爲中心，做一個半徑爲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);

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;

//客戶區設置爲白色

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

//y軸朝上

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

g.Transform = mat;

//移動座標原點到窗體中心

Rectangle rect = this.ClientRectangle;

int w = rect.Width;

int h = rect.Height;

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

//在全局座標下繪製橢圓

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);

//創建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);

}

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×alpha/255+背景色×（255－alpha）/255

protected override void OnPaint(PaintEventArgs e)
{
Graphics g = e.Graphics;

//創建一個填充矩形

SolidBrush brush = new SolidBrush(Color.BlueViolet);

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

//創建一個位圖，其中兩個位圖之間有透明效果

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);

//創建一個位圖，其中兩個位圖之間沒有透明效果

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);

}

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);

//設置反走樣

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);

}

完了。暫時先總結那麼多。以後發現必要的可以再補充。

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