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C#对一个矩形进行旋转GDI绘图，可以指定任意角度进行旋转

我们可以认为一张图片Image，本质就是一个矩形Rectangle,旋转矩形也就是旋转图片

在画图密封类 System.Drawing.Graphics中，

矩形旋转的两个关键方法

//设置旋转的中心点

public void TranslateTransform(float dx, float dy);

//旋转指定的角度【单位°】：旋转角度 从 X+ 到 Y+之间的旋转角度认为是正数

public void RotateTransform(float angle);

矩形旋转WindowsForms应用程序

新建窗体应用程序RotatedRectangleDemo，将默认的Form1重命名为FormRotatedRectangle

窗体FormRotatedRectangle设计如图：

窗体设计FormRotatedRectangle设计器代码如下：

文件FormRotatedRectangle.Designer.cs

namespace RotatedRectangleDemo
{partial class FormRotatedRectangle{/// <summary>/// 必需的设计器变量。/// </summary>private System.ComponentModel.IContainer components = null;/// <summary>/// 清理所有正在使用的资源。/// </summary>/// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>protected override void Dispose(bool disposing){if (disposing && (components != null)){components.Dispose();}base.Dispose(disposing);}#region Windows 窗体设计器生成的代码/// <summary>/// 设计器支持所需的方法 - 不要修改/// 使用代码编辑器修改此方法的内容。/// </summary>private void InitializeComponent(){this.btnRotate = new System.Windows.Forms.Button();this.label1 = new System.Windows.Forms.Label();this.numRotate = new System.Windows.Forms.NumericUpDown();((System.ComponentModel.ISupportInitialize)(this.numRotate)).BeginInit();this.SuspendLayout();// // btnRotate// this.btnRotate.Font = new System.Drawing.Font("宋体", 13F);this.btnRotate.Location = new System.Drawing.Point(271, 7);this.btnRotate.Name = "btnRotate";this.btnRotate.Size = new System.Drawing.Size(75, 33);this.btnRotate.TabIndex = 0;this.btnRotate.Text = "旋转";this.btnRotate.UseVisualStyleBackColor = true;this.btnRotate.Click += new System.EventHandler(this.btnRotate_Click);// // label1// this.label1.AutoSize = true;this.label1.Location = new System.Drawing.Point(25, 20);this.label1.Name = "label1";this.label1.Size = new System.Drawing.Size(119, 12);this.label1.TabIndex = 1;this.label1.Text = "旋转角度(0°~360°)";// // numRotate// this.numRotate.DecimalPlaces = 2;this.numRotate.Location = new System.Drawing.Point(150, 16);this.numRotate.Maximum = new decimal(new int[] {360,0,0,0});this.numRotate.Name = "numRotate";this.numRotate.Size = new System.Drawing.Size(97, 21);this.numRotate.TabIndex = 2;this.numRotate.Value = new decimal(new int[] {30,0,0,0});// // FormRotatedRectangle// this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;this.ClientSize = new System.Drawing.Size(945, 508);this.Controls.Add(this.numRotate);this.Controls.Add(this.label1);this.Controls.Add(this.btnRotate);this.Name = "FormRotatedRectangle";this.Text = "GDI旋转示例：矩形旋转任意角度";((System.ComponentModel.ISupportInitialize)(this.numRotate)).EndInit();this.ResumeLayout(false);this.PerformLayout();}#endregionprivate System.Windows.Forms.Button btnRotate;private System.Windows.Forms.Label label1;private System.Windows.Forms.NumericUpDown numRotate;}
}

旋转矩形示例代码如下：

文件FormRotatedRectangle.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;namespace RotatedRectangleDemo
{public partial class FormRotatedRectangle : Form{public FormRotatedRectangle(){InitializeComponent();/* 定义了一个名为FormRotatedRectangle的窗体类，* 它覆盖(override)了OnPaint方法来绘制旋转的矩形。* 在OnPaint方法中，我们首先设置矩形的位置和大小，然后保存图形状态，* 接着设置旋转变换的中心点，通过RotateTransform方法设置旋转角度，并绘制旋转后的矩形，最后恢复图形状态。* 程序运行时，会显示一个旋转了30度的矩形。*/}/// <summary>/// 窗体重绘事件/// </summary>/// <param name="e"></param>protected override void OnPaint(PaintEventArgs e){base.OnPaint(e);Graphics g = e.Graphics;// 设置矩形的位置和大小Rectangle rect = new Rectangle(100, 100, 200, 100);RotateRectangle(g, rect, (float)numRotate.Value);}/// <summary>/// 将初始矩形旋转指定的角度数/// </summary>/// <param name="g">窗体画图对象</param>/// <param name="rect">初始矩形对象(x,y,width,height)</param>/// <param name="rotateAngle">旋转角度，单位°</param>private void RotateRectangle(Graphics g, Rectangle rect, float rotateAngle) {// 保存原始状态GraphicsState state = g.Save();// 设置旋转的中心点为矩形的中心g.TranslateTransform(rect.X + rect.Width / 2, rect.Y + rect.Height / 2);// 旋转矩形：旋转角度 从 X+ 到 Y+之间的旋转角度认为是正数g.RotateTransform(rotateAngle);// 恢复变换的中心点g.TranslateTransform(-(rect.X + rect.Width / 2), -(rect.Y + rect.Height / 2));// 绘制矩形g.DrawRectangle(Pens.Black, rect);// 恢复图形状态g.Restore(state);}private void btnRotate_Click(object sender, EventArgs e){this.Invalidate();//引起触发重绘OnPaint事件}}
}

程序运行如图：

旋转45°【π/4】

旋转90°【π/2】