Question

C#中如何画函数图

已知一个指数函数，如何用C#画出其图形，代码最好

Answer 1

下面就是源程序：

// 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());
}
}
}

原文：http://www.cnblogs.com/skyivben/archive/2005/11/01/266649.html

Answer 2

其实，以前老师教过我们也画过，现在忘了！用代码比画的更好！如果你有《.net framework2.0程序设计》的话，上面就有怎么画的，还有代码呢

Answer 3

DrawLines
做一个循环从0到N然后把值赋给函数然后得到返回值然后将返回值和之前这个值做成一个POINT装入一个POINT数组，之后用DrawLines

Answer 4

DrawLines
做一个循环从0到N然后把值赋给函数然后得到返回值然后将返回值和之前这个值做成一个POINT装入一个POINT数组，之后用DrawLines

Answer 5

就那么画呗，根据你的线是直线还是曲线。然后根据预设的坐标轴的单位。
简单流程就是
1设置个画布Graphics
2在画布上铺上背景
3画坐标轴
4根据你的函数画线Graphics的Draw...方法。