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c#,gdi+,画函数图形,坐标系,如f(x)=sin(x)

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// Expression.cs - 动态生成数学表达式并计算其值

// 表达式使用 C# 语法，可带一个的自变量(x)。

// 表达式的自变量和值均为(double)类型。

// 使用举例:

// Expression expression = new Expression("Math.Sin(x)");

// Console.WriteLine(expression.Compute(Math.PI / 2));

// expression = new Expression("double u = Math.PI - x;" +

// "double pi2 = Math.PI * Math.PI;" +

// "return 3 * x * x + Math.Log(u * u) / pi2 / pi2 + 1;");

// Console.WriteLine(expression.Compute(0));
using System;

using System.CodeDom.Compiler;

using Microsoft.CSharp;

using System.Reflection;

using System.Text;
namespace Skyiv.Util

{

sealed class Expression

{

object instance;

MethodInfo method;
public Expression(string expression)

{

if (expression.IndexOf("return") < 0) expression = "return " + expression + ";";

string className = "Expression";

string methodName = "Compute";

CompilerParameters p = new CompilerParameters();

p.GenerateInMemory = true;

CompilerResults cr = new CSharpCodeProvider().CompileAssemblyFromSource(p, string.

Format("using System;sealed class {0}{{public double {1}(double x){{{2}}}}}",

className, methodName, expression));

if (cr.Errors.Count > 0)

{

string msg = "Expression(\"" + expression + "\"): \n";

foreach (CompilerError err in cr.Errors) msg += err.ToString() + "\n";

throw new Exception(msg);

}

instance = cr.CompiledAssembly.CreateInstance(className);

method = instance.GetType().GetMethod(methodName);

}
public double Compute(double x)

{

return (double)method.Invoke(instance, new object[] { x });

}

}

}
// plot.cs: 画函数图形, 编译方法: csc /t:winexe plot.cs Expression.cs

using System;

using System.Drawing;

using System.Windows.Forms;

using Skyiv.Util;
namespace Skyiv.Ben.Plot

{

sealed class PlotForm : Form

{

const int yBase = 24; // 屏幕保留区域的高度
TextBox tbxX0, tbxX1; // 函数自变量的取值范围

TextBox tbxExpression; // 函数的表达式
PlotForm()

{

SuspendLayout();
Button btnSubmit = new Button();

btnSubmit.Text = "刷新";

btnSubmit.Location = new Point(0, 0);

btnSubmit.Size = new Size(48, 24);

btnSubmit.Click += new EventHandler(BtnSubmit_Click);
tbxX0 = new TextBox();

tbxX0.Text = "-Math.PI";

tbxX0.Location = new Point(55, 3);

tbxX0.Size = new Size(100, 20);
tbxX1 = new TextBox();

tbxX1.Text = "Math.PI";

tbxX1.Location = new Point(160, 3);

tbxX1.Size = new Size(100, 20);
tbxExpression = new TextBox();

tbxExpression.Text = "Math.Sin(x)";

tbxExpression.Location = new Point(265, 3);

tbxExpression.Size = new Size(335, 20);

tbxExpression.Anchor = (AnchorStyles.Top | AnchorStyles.Left | AnchorStyles.Right);
Controls.AddRange(new Control[] { btnSubmit, tbxX0, tbxX1, tbxExpression });

Text = "Plot";

BackColor = Color.White;

ClientSize = new Size(600, 600 + yBase);

// WindowState = FormWindowState.Maximized;
ResumeLayout(false);

}
// 点击“刷新”按钮时重绘程序主窗口

void BtnSubmit_Click(object sender, EventArgs e)

{

Invalidate();

}
/*

// 因为本程序使用 C# 的反射功能动态生成数学表达式并计算其值

// 所以重画时有点慢，如果你的计算机的速度不是非常快的，

// 就不要在窗口改变大小时强制重绘，而是通过点击发“刷新”按钮重绘。

protected override void OnSizeChanged(EventArgs e)

{

Invalidate();

base.OnSizeChanged(e);

}

*/
protected override void OnPaint(PaintEventArgs e)

{

Graphics gc = e.Graphics;

try

{

double x0 = new Expression(tbxX0.Text).Compute(0);

double x1 = new Expression(tbxX1.Text).Compute(0);

Size size = ClientSize;

int i0 = 0;

int i1 = size.Width - 1;

int j0 = yBase;

int j1 = size.Height - 1;

Pen pen = new Pen(Color.Black, 1);

gc.DrawLine(pen, i0, j0, i1, j0); // 画图区和保留区的分界线

double rx = (x1 - x0) / (i1 - i0);

double y0, y1;

Expression fx = new Expression(tbxExpression.Text);

GetFunctionValueRange(fx, x0, rx, i0, i1, out y0, out y1);

double ry = (y1 - y0) / (j1 - j0);

Out(gc, 0, "ClientSize: {0}x{1}", i1 - i0 + 1, j1 - j0 + 1);

Out(gc, 1, "f(x): " + tbxExpression.Text);

Out(gc, 2, "x:[{0}, {1}] range:{2}", x0, x1, x1 - x0);

Out(gc, 3, "y:[{0}, {1}] range:{2}", y0, y1, y1 - y0);

Out(gc, 4, "rx:{0}", 1 / rx); // 函数自变量每单位值用多少个象素表示

Out(gc, 5, "ry:{0}", 1 / ry); // 函数的值每单位值用多少个象素表示

Out(gc, 6, "r :{0}", rx / ry); // 该值如果小于1表示图形纵向被压扁，反之则被拉伸

pen.Color = Color.Green;

int j = j1 + (int)(y0 / ry);

if (j >= j0 && j <= j1) gc.DrawLine(pen, i0, j, i1, j); // x坐标轴

int i = i0 - (int)(x0 / rx);

if (i >= i0 && i <= i1) gc.DrawLine(pen, i, j0, i, j1); // y坐标轴

pen.Color = Color.Red;

for (i = i0; i <= i1; i++)

{

double x = x0 + (i - i0) * rx;

double y = fx.Compute(x);

if (double.IsInfinity(y) || double.IsNaN(y)) continue;

j = j1 - (int)((y - y0) / ry);

if (j > j1 || j < j0) continue;

gc.DrawLine(pen, i, j, i + 1, j); // 画函数的图形

}

}

catch (Exception ex)

{

Out(gc, 0, ex.Message);

}

base.OnPaint(e);

}
// 函数值的取值范围

void GetFunctionValueRange(Expression fx, double x0, double rx, int i0, int i1, out double y0, out double y1)

{

y0 = double.MaxValue;

y1 = double.MinValue;

for (int i = i0; i <= i1; i++)

{

double x = x0 + (i - i0) * rx;

double y = fx.Compute(x);

if (double.IsInfinity(y) || double.IsNaN(y)) continue;

if (y0 > y) y0 = y;

if (y1 < y) y1 = y;

}

}
// 在指定的位置写字符串

void Out(Graphics gc, int line, string fmt, params object[] args)

{

gc.DrawString(string.Format(fmt, args), new Font("Courier New", 10), Brushes.Blue, new PointF(5, yBase + 15 * line));

}
static void Main()

{

Application.Run(new PlotForm());

}

}

}

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