摘要

在C#开发中，使用GDI+（Graphics Device Interface Plus）库可以轻松地实现图形绘制功能，包括绘制线条。本文将介绍GDI+中常用的绘制线的方法与属性，并提供一些实际应用的示例。

正文

GDI+是Windows平台上用于图形绘制的API，它提供了丰富的功能来绘制图像、文本、形状等元素。要使用GDI+进行线条绘制，首先需要引入System.Drawing命名空间。

常用方法与属性

Pen类的常用属性

• Color：设置或获取画笔的颜色。
• Width：设置或获取画笔的宽度。
• DashStyle：设置或获取线条的样式（实线、虚线等）。
• StartCap和EndCap：设置或获取线条的起始和结束端点样式。
• LineJoin：设置或获取线条的连接方式。

Graphics类的常用方法

• DrawLine：绘制线条。
• DrawLines：绘制多条线条。
• DrawArc：绘制弧线。

1. 绘制一个简单的直角三角形

C#
protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);
    Graphics graphics = e.Graphics;
    Pen pen = new Pen(Color.Blue, 3);

    Point point1 = new Point(50, 50);
    Point point2 = new Point(50, 150);
    Point point3 = new Point(150, 150);

    graphics.DrawLine(pen, point1, point2);
    graphics.DrawLine(pen, point2, point3);
    graphics.DrawLine(pen, point3, point1);

    graphics.Dispose();
    pen.Dispose();

}

2. 绘制一个彩虹

C#
protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);
    Graphics graphics = e.Graphics;
    string[] colors = { "Violet", "Indigo", "Blue", "Green", "Yellow", "Orange", "Red" };

    for (int i = 0; i < colors.Length; i++)
    {
        Color color = Color.FromName(colors[i]);
        Pen pen = new Pen(color, 20);
        graphics.DrawLine(pen, i * 50 + 20, 100, i * 50 + 70, 100);
        pen.Dispose();
    }

}

3. 用DrawArc绘制一个彩虹

C#
protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);
    Graphics graphics = e.Graphics;
    // 启用抗锯齿效果
    graphics.SmoothingMode = SmoothingMode.AntiAlias;
    int centerX = this.ClientSize.Width / 2;
    int centerY = this.ClientSize.Height / 2;

    string[] colors = { "Violet", "Indigo", "Blue", "Green", "Yellow", "Orange", "Red" };
    float startAngle = 180.0f; // 起始角度
    float sweepAngle = 180.0f; // 扫描角度

    for (int i = 0; i < colors.Length; i++)
    {
        Color color = Color.FromName(colors[i]);
        Pen pen = new Pen(color, 30);
        RectangleF arcRect = new RectangleF(centerX - i * 30, centerY - i * 30, (i+1) * 60, (i + 1) * 60);

        graphics.DrawArc(pen, arcRect, startAngle, sweepAngle);
        pen.Dispose();
    }
}

protected override void OnResize(EventArgs e)
{
    base.OnResize(e);
    this.Refresh();
}

4. 绘制一个正玄函数

C#
public Form1()
{
    InitializeComponent();

    this.DoubleBuffered = true;
    this.Paint += new PaintEventHandler(SineWavePlot_Paint);
}

private void SineWavePlot_Paint(object sender, PaintEventArgs e)
{
    Graphics graphics = e.Graphics;

    int width = this.ClientSize.Width;
    int height = 400;

    Pen pen = new Pen(Color.Blue, 2);

    graphics.SmoothingMode= SmoothingMode.AntiAlias;

    // 绘制坐标轴
    graphics.DrawLine(pen, 50, height - 50, width - 50, height - 50); // x轴
    graphics.DrawLine(pen, 50, 50, 50, height - 50); // y轴

    // 绘制平滑的正弦函数曲线
    PointF[] dataPoints = new PointF[10001];
    double step = (2 * Math.PI) / 10000; // 步长为2π/10000，表示0到2π之间的弧度范围

    for (int i = 0; i <= 10000; i++)
    {
        double x = i * step;
        double y = Math.Sin(x); // 正弦函数
        int plotX = (int)(x * 100 + width / 10);
        int plotY = (int)(y * 100 + height / 2);
        dataPoints[i] = new PointF(plotX, plotY);
    }

    graphics.DrawLines(pen, dataPoints);

    pen.Dispose();
}

protected override void OnResize(EventArgs e)
{
    base.OnResize(e);
    this.Refresh();
}