GDI+编程的10个基本技巧
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); }