实现方案：
实现并不是特别复杂，每条显示的字符串都作为一个WordInfo对象，该对象包含了速度、颜色、字体大小、字符个数等属性。在控件类WordRain中在该项目中，定义了两个Timer，一个是m_timer用来定时重绘控件，一个是m_newtimer用来定时创建新的WordInfo对象。在WordRain中还维持了两个ArrayList，一个是m_selectlist用来显示要绘制的字符（每次重绘控件的时候都会随机获取m_charlist中的一个字符用于显示），一个是m_charlist用来保存当前显示在控件中的WordInfo对象（超出控件范围的对象要及时删除）。
注意点和相关处理如下：
1. 字体较大字符串的必需在字体小的字符串之后画，避免字体小的字符串遮住字体大的字符串，影响效果。
要达到这样的效果必须在每次重绘的时候，对m_charlist中的所有WordInfo对象按字体大小从小到大排序。实现如下：
public class WordInfoSorter : IComparer
{
int IComparer.Compare(object x, object y)
{
if (((WordInfo)x).m_fontsize < ((WordInfo)y).m_fontsize) return -1;
else if (((WordInfo)x).m_fontsize == ((WordInfo)y).m_fontsize) return 0;
else return 1;
}
}
public partial class WordRain : UserControl
{
//...
private WordInfoSorter m_sorter;
//...
public WordRain()
{
//...
m_sorter = new WordInfoSorter();
//...
}
//...
private void WordRain_Paint(object sender, PaintEventArgs e)
{
//...
m_charlist.Sort(m_sorter);
//...
}
2. 为了保证效果，字体较大的字符串颜色要接近前景色m_min_charcolor，字体较小的字符串颜色要更接近背景色m_max_charcolor。颜色根据字体的最大值和最小值来计算）。详见类WordInfo的SetFontAndColor()方法。
3. 同样为了保证效果，每个字符串有 m_count个字符，显示在最下面的字符颜色100%不透明，显示在最上面的字符颜色最接近透明。详见类WordInfo的GetColor()方法。
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Data;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Collections;
using System.Runtime.InteropServices;
namespace myControl
{
public partial class WordRain : UserControl
{
private Timer m_timer; //重绘定时器
private Timer m_newtimer; //新建字符定时器
private Graphics m_g; //画布
private ArrayList m_charlist;
private ArrayList m_selectlist;
private WordInfoSorter m_sorter;
private Random m_random;
public WordRain()
{
InitializeComponent();
this.SetStyle(ControlStyles.UserPaint, true);
this.SetStyle(ControlStyles.AllPaintingInWmPaint, true);
this.SetStyle(ControlStyles.OptimizedDoubleBuffer, true);
this.SetStyle(ControlStyles.ResizeRedraw, true);
this.SetStyle(ControlStyles.Selectable, true);
this.BackColor = Color.Black;
m_charlist = new ArrayList();
WordInfo wordinfo = new WordInfo();
wordinfo.SetValue();
m_charlist.Add(wordinfo);
m_sorter = new WordInfoSorter();
string[] arr = new string[] {"0","1","2","3","4","5","6","7","8","9"};
m_selectlist = new ArrayList(arr);
m_random = new Random();
m_timer = new Timer();
m_newtimer = new Timer();
m_timer.Interval = 10;
m_newtimer.Interval = 50;
m_timer.Enabled = true;
m_newtimer.Enabled = true;
m_timer.Tick += new EventHandler(m_timer_Tick);
m_newtimer.Tick += new EventHandler(m_newtimer_Tick);
}
private string GetStringFromArrayList()
{
return (string)m_selectlist[m_random.Next(m_selectlist.Count)];
}
void m_newtimer_Tick(object sender, EventArgs e)
{
WordInfo wordinfo = new WordInfo();
wordinfo.SetValue();
m_charlist.Add(wordinfo);
}
void m_timer_Tick(object sender, EventArgs e)
{
this.Invalidate();
ArrayList ObjToDel = new ArrayList();
foreach (WordInfo temp in m_charlist)
{
temp.m_posy += temp.m_runspeed;
if (temp.m_posy > this.Height + temp.m_fontsize * temp.m_count)
ObjToDel.Add(temp);
}
foreach (WordInfo temp in ObjToDel)
{
m_charlist.Remove(temp);
}
ObjToDel.Clear();
}
private void WordRain_Paint(object sender, PaintEventArgs e)
{
m_g = e.Graphics;
m_charlist.Sort(m_sorter);
SetXRange(this.Width);
foreach (WordInfo temp in m_charlist)
{
using (Font font = new Font("Arial", temp.m_fontsize, GraphicsUnit.Pixel))
{
using(SolidBrush brush = new SolidBrush(temp.m_charcolor))
{
for (int i = 0; i < temp.m_count; i++)
{
brush.Color = temp.GetColor(i);
m_g.DrawString(GetStringFromArrayList(), font, brush, temp.m_posx, temp.m_posy-temp.m_fontsize*i);
}
}
}
}
}
//设置字体大小范围
public void SetFontSizeRange(int minsize, int maxsize)
{
if (minsize > maxsize)
{
throw new ArgumentException("参数minsize必须小于等于参数maxsize");
}
if (minsize < 1 || maxsize > 50)
{
throw new ArgumentException("参数minsize和maxsize必须在区间[1,50]内");
}
WordInfo.m_min_fontsize = minsize;
WordInfo.m_max_fontsize = maxsize;
}
//设置字体渐变颜色范围
public void SetFontColorRange(Color firstColor, Color lastColor)
{
WordInfo.m_min_charcolor = firstColor;
WordInfo.m_max_charcolor = lastColor;
}
//设置X轴所能到达的最大长度(即控件的宽度)
public void SetXRange(int value)
{
WordInfo.m_max_xpos = value;
}
//设置速度
public void SetSpeedRange(float minspeed, float maxspeed)
{
if (minspeed > maxspeed)
{
throw new ArgumentException("参数minspeed必须小于等于参数maxspeed");
}
if (minspeed < 0.1 || maxspeed > 100.0)
{
throw new ArgumentException("参数minspeed和maxspeed必须在区间[0.1,100.0]内");
}
WordInfo.m_min_runspeed = minspeed;
WordInfo.m_min_runspeed = maxspeed;
}
//设置字符个数范围
public void SetCountRange(int mincount, int maxcount)
{
if (mincount > maxcount)
{
throw new ArgumentException("参数mincount必须小于等于参数maxcount");
}
if (mincount < 1 || maxcount > 100)
{
throw new ArgumentException("参数mincount和maxcount必须在区间[1,100]内");
}
WordInfo.m_min_count = mincount;
WordInfo.m_max_count = maxcount;
}
//设置字符列表
public void SetArrayValue(ArrayList list)
{
if (list.Count == 0)
{
throw new ArgumentException("参数list中的元素个数不能为0");
}
m_selectlist.Clear();
m_selectlist = list;
}
}
public class WordInfoSorter : IComparer
{
int IComparer.Compare(object x, object y)
{
if (((WordInfo)x).m_fontsize < ((WordInfo)y).m_fontsize) return -1;
else if (((WordInfo)x).m_fontsize == ((WordInfo)y).m_fontsize) return 0;
else return 1;
}
}
public class WordInfo
{
public int m_fontsize; //字体大小
public float m_runspeed; //移动速度
public Color m_charcolor; //最下面的字的颜色，最上面的字的颜色为背景色
public float m_posx; //横坐标
public float m_posy; //纵坐标
public int m_count; //字符个数
public ArrayList m_charList; //要显示的字符列表
public static int m_max_xpos = 600;
public static int m_min_count = 10;
public static int m_max_count = 20;
public static int m_min_fontsize = 4;
public static int m_max_fontsize = 20;
public static float m_min_runspeed = 0.6F;
public static float m_max_runspeed = 4.2F;
public static Color m_min_charcolor = Color.FromArgb(0, 255, 0);
public static Color m_max_charcolor = Color.FromArgb(0, 55, 0);
public static Random m_random = new Random();
public WordInfo()
{
this.m_count = 1;
this.m_fontsize = 0;
this.m_runspeed = 0;
this.m_posx = 0;
this.m_posy = 0;
this.m_charcolor = Color.FromArgb(0, 255, 0);
}
//获取字体大小的随机值
private int GetFontSize()
{
int i = m_random.Next();
return i % (m_max_fontsize - m_min_fontsize) + m_min_fontsize;
}
//获取速度的随机值
private float GetSpeed()
{
int i = m_random.Next();
int j = m_random.Next();
return i % (m_max_runspeed - m_min_runspeed) + m_min_runspeed+ (j%10)/10.0F;
}
//获取颜色的随机值
private Color GetColor()
{
int min_r = m_min_charcolor.R;
int min_g = m_min_charcolor.G;
int min_b = m_min_charcolor.B;
int max_r = m_max_charcolor.R;
int max_g = m_max_charcolor.G;
int max_b = m_max_charcolor.B;
int r = m_random.Next((min_r > max_r ? max_r : min_r), (min_r < max_r ? max_r : min_r));
int g = m_random.Next((min_g > max_g ? max_g : min_g), (min_g < max_g ? max_g : min_g));
int b = m_random.Next((min_b > max_b ? max_b : min_b), (min_b < max_b ? max_b : min_b));
return Color.FromArgb(r, g, b);
}
//设置字体和颜色(字体越小，颜色越接近m_max_charcolor)
private void SetFontAndColor()
{
int i = m_random.Next();
int fontpart = i % (m_max_fontsize - m_min_fontsize);
this.m_fontsize = m_min_fontsize + fontpart;
float percent = ((float)fontpart) / ((float)(m_max_fontsize - m_min_fontsize));
int min_r = m_min_charcolor.R;
int min_g = m_min_charcolor.G;
int min_b = m_min_charcolor.B;
int max_r = m_max_charcolor.R;
int max_g = m_max_charcolor.G;
int max_b = m_max_charcolor.B;
int rpart = (int)(Math.Abs(min_r - max_r) * percent);
int gpart = (int)(Math.Abs(min_g - max_g) * percent);
int bpart = (int)(Math.Abs(min_b - max_b) * percent);
int r = min_r > max_r ? (max_r + rpart) : (max_r - rpart);
int g = min_g > max_g ? (max_g + gpart) : (max_g - gpart);
int b = min_b > max_b ? (max_b + bpart) : (max_b - bpart);
this.m_charcolor = Color.FromArgb(r, g, b);
}
//获取x轴坐标
private float GetXPos()
{
int i = m_random.Next(m_max_xpos-1);
return (float)(i + m_random.Next(10) / 10.0F);
}
//获取随机个数
private int GetCount()
{
return m_random.Next(m_min_count, m_max_count);
}
//设置相关值
public void SetValue()
{
this.m_count = this.GetCount();
this.SetFontAndColor();
this.m_runspeed = this.GetSpeed();
this.m_posy = m_count*m_fontsize*(-1.0F);
this.m_posx = this.GetXPos();
}
//获取颜色
public Color GetColor(int index)
{
if (this.m_count == 1)
return this.m_charcolor;
if (index == 0)
return this.m_charcolor;
int rpart = (Math.Abs(m_charcolor.R - m_max_charcolor.R)) / m_count * index;
int gpart = (Math.Abs(m_charcolor.G - m_max_charcolor.G)) / m_count * index;
int bpart = (Math.Abs(m_charcolor.B - m_max_charcolor.B)) / m_count * index;
int r = m_charcolor.R > m_max_charcolor.R ? (m_charcolor.R - rpart) : (m_charcolor.R + rpart);
int g = m_charcolor.G > m_max_charcolor.G ? (m_charcolor.G - gpart) : (m_charcolor.G + gpart);
int b = m_charcolor.B > m_max_charcolor.B ? (m_charcolor.B - bpart) : (m_charcolor.B + bpart);
return Color.FromArgb(255-index*255/m_count, m_charcolor);
}
}
}
原文：http://blog.csdn.net/qian_f/article/details/19285075