制作印章来说，主要是如何让字均匀的显示在弧线段上，那么一般的印章要么以圆或者椭圆为底图，不过这两者的算法大致相同，为了方便说明，如下就用相对简单的圆来举例说明，如果需要做椭圆的话，可以在我的基础上进行扩展，因为核心算法是一样的，相对于圆来说，椭圆求弧长以及各个字符的位置，这两点相对麻烦些，但是这两者都可找到相应的数学公式。
这里首先提一点，我这篇文章部分借鉴了codeproject的一个例子，原文可以参看如下地址。
http://www.codeproject.com/vb/net/Text_on_Path_with_VBNET.asp
（说实话，这篇文章写得有些乱，而且对于buffer的操作近乎于疯狂）
由于印章的实现相对于这篇文章来说，相对简单多了，而且规律性很强，因此我自己考虑重新组织算法进行实现。
那么实现一个印章，大致步骤如下。
1． 计算字符串总长度，以及各个字符的长度；
2． 计算出字符串的起始角度；
3． 求出每个字符的所在的点，以及相对于中心的角度；
4． 绘制每个字符。
计算字符串总长度，以及各个字符的长度
这里需要用到“Graphics.MeasureString”和“Graphics.MeasureCharacterRanges”这两个方法，由于前者算出来的总长度有问题，所以需要后面进行重新计算（此外，这里我还考虑了字符最后显示方向）。
这部分的代码如下：
/// <summary>
/// Compute string total length and every char length
/// </summary>
/// <param name="sText"></param>
/// <param name="g"></param>
/// <param name="fCharWidth"></param>
/// <param name="fIntervalWidth"></param>
/// <returns></returns>
private float ComputeStringLength( string sText, Graphics g, float[] fCharWidth,
float fIntervalWidth,
Char_Direction Direction )
{
// Init string format
StringFormat sf = new StringFormat();
sf.Trimming = StringTrimming.None;
sf.FormatFlags = StringFormatFlags.NoClip | StringFormatFlags.NoWrap
| StringFormatFlags.LineLimit;
// Measure whole string length
SizeF size = g.MeasureString( sText, _font, (int)_font.Style );
RectangleF rect = new RectangleF( 0f,0f, size.Width, size.Height );
// Measure every character size
CharacterRange[] crs = new CharacterRange[sText.Length];
for( int i = 0; i < sText.Length; i++ )
crs[i] = new CharacterRange( i, 1 );
// Reset string format
sf.FormatFlags = StringFormatFlags.NoClip;
sf.SetMeasurableCharacterRanges( crs );
sf.Alignment = StringAlignment.Near;
// Get every character size
Region[] regs = g.MeasureCharacterRanges( sText,
_font, rect, sf );
// Re-compute whole string length with space interval width
float fTotalWidth = 0f;
for( int i = 0; i < regs.Length; i++ )
{
if( Direction == Char_Direction.Center || Direction == Char_Direction.OutSide )
fCharWidth[i] = regs[i].GetBounds( g ).Width;
else
fCharWidth[i] = regs[i].GetBounds( g ).Height;
fTotalWidth += fCharWidth[i] + fIntervalWidth;
}
fTotalWidth -= fIntervalWidth;//Remove the last interval width
return fTotalWidth;
}
计算出字符串的起始角度
为了更好地开展文章，那么首先说说在我这篇文章中，坐标的度数位置。详情参看如下图示。
对于图形角度分布有个概念后，那么对于整个字符串所跨的弧度以及起始弧度的计算，就相对比较简单了。具体如下：
// Compute arc's start-angle and end-angle
double fStartAngle, fSweepAngle;
fSweepAngle = fTotalWidth * 360 / ( _rectcircle.Width * Math.PI );
fStartAngle = 270 - fSweepAngle / 2;
求出每个字符的所在的点，以及相对于中心的角度
这一部分相对要麻烦些，大致步骤如下。
1． 通过字符长度，求出字符所跨的弧度；
2． 根据字符所跨的弧度，以及字符起始位置，算出字符的中心位置所对应的角度；
3． 由于相对中心的角度已知，根据三角公式很容易算出字符所在弧上的点，如下图所示；
4． 根据字符长度以及间隔距离，算出下一个字符的起始角度；
5． 重复1直至整个字符串结束。
那么这部分的具体代码如下。
/// <summary>
/// Compute every char position
/// </summary>
/// <param name="CharWidth"></param>
/// <param name="recChars"></param>
/// <param name="CharAngle"></param>
/// <param name="StartAngle"></param>
private void ComputeCharPos(
float[] CharWidth,
PointF[] recChars,
double[] CharAngle,
double StartAngle )
{
double fSweepAngle, fCircleLength;
//Compute the circumference
fCircleLength = _rectcircle.Width * Math.PI;
for( int i = 0; i < CharWidth.Length; i++ )
{
//Get char sweep angle
fSweepAngle = CharWidth[i] * 360 / fCircleLength;
//Set point angle
CharAngle[i] = StartAngle + fSweepAngle / 2;
//Get char position
if( CharAngle[i] < 270f )
recChars[i] = new PointF(
_rectcircle.X + _rectcircle.Width / 2
-(float)( _rectcircle.Width / 2 *
Math.Sin( Math.Abs( CharAngle[i] - 270 ) * Math.PI / 180 ) ) ,
_rectcircle.Y + _rectcircle.Width / 2
-(float)( _rectcircle.Width / 2 * Math.Cos(
Math.Abs( CharAngle[i] - 270 ) * Math.PI / 180 ) ) );
else
recChars[i] = new PointF(
_rectcircle.X + _rectcircle.Width / 2
+(float)( _rectcircle.Width / 2 *
Math.Sin( Math.Abs( CharAngle[i] - 270 ) * Math.PI / 180 ) ) ,
_rectcircle.Y + _rectcircle.Width / 2
-(float)( _rectcircle.Width / 2 * Math.Cos(
Math.Abs( CharAngle[i] - 270 ) * Math.PI / 180 ) ) );
//Get total sweep angle with interval space
fSweepAngle = ( CharWidth[i] + _letterspace ) * 360 / fCircleLength;
StartAngle += fSweepAngle;
}
}
绘制每个字符
由于每个字符所在的点以及相对于圆心的角度都已经计算出来，那么进行绘制就相对简单多了，这里只是通过Matrix来转换一下坐标而已。
具体代码如下。
/// <summary>
/// Draw every rotated character
/// </summary>
/// <param name="g"></param>
/// <param name="_text"></param>
/// <param name="_angle"></param>
/// <param name="_PointCenter"></param>
private void DrawRotatedText( Graphics g, string _text, float _angle, PointF _PointCenter )
{
// Init format
StringFormat sf = new StringFormat();
sf.Alignment = StringAlignment.Center;
sf.LineAlignment = StringAlignment.Center;
// Create graphics path
GraphicsPath gp = new GraphicsPath( System.Drawing.Drawing2D.FillMode.Winding );
int x = (int)_PointCenter.X;
int y = (int)_PointCenter.Y;
// Add string
gp.AddString( _text, _font.FontFamily, (int)_font.Style,
_font.Size, new Point( x, y ), sf );
// Rotate string and draw it
Matrix m = new Matrix();
m.RotateAt( _angle, new PointF( x,y ) );
g.Transform = m;
g.DrawPath( new Pen( _color), gp );
g.FillPath( new SolidBrush( _fillcolor ), gp );
}
以上就是绘制印章的核心算法。对于这个类的调用，如下即可。
TextOnSeal _top = new TextOnSeal();
_top.TextFont = new Font("宋体", 16, FontStyle.Regular);
_top.FillColor = Color.Red;
_top.ColorTOP = Color.Black;
_top.Text = "中华人民共和国";
_top.BaseString = "愚翁专用章";
_top.ShowPath = true;
_top.LetterSpace = 20;
_top.SealSize = 180;
_top.CharDirection = Char_Direction.Center;
_top.SetIndent( 20 );
Graphics g = this.CreateGraphics();
g.DrawImage( _top.TextOnPathBitmap(), 0, 0 );
_top.CharDirection = Char_Direction.ClockWise;
g.DrawImage( _top.TextOnPathBitmap(), 180, 0 );
_top.CharDirection = Char_Direction.AntiClockWise;
g.DrawImage( _top.TextOnPathBitmap(), 0, 180 );
_top.SetIndent( 20 );
_top.CharDirection = Char_Direction.OutSide;
g.DrawImage( _top.TextOnPathBitmap(), 180, 180 );
通过如上的代码，可以得到如下的效果。
其实如果做印章来说，还有很多地方需要细化，那么如果网友对此有兴趣，可以在我的基础上进行扩展，在此我就不一一述说。
如下是整个类的完整代码。
//--------------------------- TextOnSeal class ---------------------------------------
//------------------------------------------------------------------------------------
//---File: TextOnSeal
//---Description: The class file to create seal bitmap with text
//---Author: Knight
//---Date: Nov.3, 2006
//------------------------------------------------------------------------------------
//---------------------------{TextOnSeal class}---------------------------------------
namespace Seal
{
using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Diagnostics;
/// <summary>
/// Summary description for TextOnSeal.
/// </summary>
public class TextOnSeal
{
private string _text;
private Font _font;
private Color _pathcolor = Color.Red;
private Color _color = Color.Black;
private Color _fillcolor = Color.Black;
private int _letterspace = 10;
private bool _showpath = true;
private Rectangle _rectcircle;
private Rectangle _rect;
private int _intentlength = 10;
private Char_Direction _chardirect = Char_Direction.Center;
private int _degree = 90;
private string _basestring;
#region Class_Properties
public Char_Direction CharDirection
{
get{ return _chardirect;}
set{
if( _chardirect != value )
{
_chardirect = value;
switch( _chardirect )
{
case Char_Direction.Center:
_degree = 90;
break;
case Char_Direction.ClockWise:
_degree = 0;
break;
case Char_Direction.OutSide:
_degree = -90;
break;
case Char_Direction.AntiClockWise:
_degree = 180;
break;
}
}
}
}
public string BaseString
{
get{ return _basestring;}
set{ _basestring = value; }
}
public string Text
{
get{ return _text;}
set{ _text = value;}
}
public Font TextFont
{
get{ return _font;}
set{ _font = value;}
}
public Color PathColor
{
get{ return _pathcolor;}
set{ _pathcolor = value; }
}
public Color ColorTOP
{
get{ return _color;}
set{ _color = value;}
}
public Color FillColor
{
get{ return _fillcolor;}
set{ _fillcolor = value;}
}
public int LetterSpace
{
get{ return _letterspace;}
set{ _letterspace = value;}
}
public bool ShowPath
{
get{ return _showpath;}
set{ _showpath = value;}
}
public int SealSize
{
set{
_rect = new Rectangle( 0, 0, value, value );
_rectcircle = new Rectangle(
new Point( _rect.X + _intentlength, _rect.Y + _intentlength ),
new Size( _rect.Width - 2 * _intentlength, _rect.Height - 2 * _intentlength ) ) ;
}
}
#endregion {Class_Properties}
public void SetIndent( int IntentLength )
{
_intentlength = IntentLength;
_rectcircle = new Rectangle( _intentlength, _intentlength,
_rect.Width - _intentlength * 2, _rect.Height - _intentlength * 2 );
}
public TextOnSeal()
{
//
// TODO: Add constructor logic here
//
}
public Bitmap TextOnPathBitmap(
Rectangle rectCircle,
string strText,
Font fntText,
Color clrColor,
Color clrFill,
int nPercentage )
{
_rect = rectCircle;
_rectcircle = new Rectangle(
new Point( _rect.X + _intentlength, _rect.Y + _intentlength ),
new Size( _rect.Width - 2 * _intentlength, _rect.Height - 2 * _intentlength ) ) ;
_text = strText;
_font = fntText;
_color = clrColor;
_fillcolor = clrFill;
_letterspace = nPercentage;
return TextOnPathBitmap();
}
/// <summary>
/// Compute string total length and every char length
/// </summary>
/// <param name="sText"></param>
/// <param name="g"></param>
/// <param name="fCharWidth"></param>
/// <param name="fIntervalWidth"></param>
/// <returns></returns>
private float ComputeStringLength( string sText, Graphics g, float[] fCharWidth,
float fIntervalWidth,
Char_Direction Direction )
{
// Init string format
StringFormat sf = new StringFormat();
sf.Trimming = StringTrimming.None;
sf.FormatFlags = StringFormatFlags.NoClip | StringFormatFlags.NoWrap
| StringFormatFlags.LineLimit;
// Measure whole string length
SizeF size = g.MeasureString( sText, _font, (int)_font.Style );
RectangleF rect = new RectangleF( 0f,0f, size.Width, size.Height );
// Measure every character size
CharacterRange[] crs = new CharacterRange[sText.Length];
for( int i = 0; i < sText.Length; i++ )
crs[i] = new CharacterRange( i, 1 );
// Reset string format
sf.FormatFlags = StringFormatFlags.NoClip;
sf.SetMeasurableCharacterRanges( crs );
sf.Alignment = StringAlignment.Near;
// Get every character size
Region[] regs = g.MeasureCharacterRanges( sText,
_font, rect, sf );
// Re-compute whole string length with space interval width
float fTotalWidth = 0f;
for( int i = 0; i < regs.Length; i++ )
{
if( Direction == Char_Direction.Center || Direction == Char_Direction.OutSide )
fCharWidth[i] = regs[i].GetBounds( g ).Width;
else
fCharWidth[i] = regs[i].GetBounds( g ).Height;
fTotalWidth += fCharWidth[i] + fIntervalWidth;
}
fTotalWidth -= fIntervalWidth;//Remove the last interval width
return fTotalWidth;
}
/// <summary>
/// Compute every char position
/// </summary>
/// <param name="CharWidth"></param>
/// <param name="recChars"></param>
/// <param name="CharAngle"></param>
/// <param name="StartAngle"></param>
private void ComputeCharPos(
float[] CharWidth,
PointF[] recChars,
double[] CharAngle,
double StartAngle )
{
double fSweepAngle, fCircleLength;
//Compute the circumference
fCircleLength = _rectcircle.Width * Math.PI;
for( int i = 0; i < CharWidth.Length; i++ )
{
//Get char sweep angle
fSweepAngle = CharWidth[i] * 360 / fCircleLength;
//Set point angle
CharAngle[i] = StartAngle + fSweepAngle / 2;
//Get char position
if( CharAngle[i] < 270f )
recChars[i] = new PointF(
_rectcircle.X + _rectcircle.Width / 2
-(float)( _rectcircle.Width / 2 *
Math.Sin( Math.Abs( CharAngle[i] - 270 ) * Math.PI / 180 ) ) ,
_rectcircle.Y + _rectcircle.Width / 2
-(float)( _rectcircle.Width / 2 * Math.Cos(
Math.Abs( CharAngle[i] - 270 ) * Math.PI / 180 ) ) );
else
recChars[i] = new PointF(
_rectcircle.X + _rectcircle.Width / 2
+(float)( _rectcircle.Width / 2 *
Math.Sin( Math.Abs( CharAngle[i] - 270 ) * Math.PI / 180 ) ) ,
_rectcircle.Y + _rectcircle.Width / 2
-(float)( _rectcircle.Width / 2 * Math.Cos(
Math.Abs( CharAngle[i] - 270 ) * Math.PI / 180 ) ) );
//Get total sweep angle with interval space
fSweepAngle = ( CharWidth[i] + _letterspace ) * 360 / fCircleLength;
StartAngle += fSweepAngle;
}
}
/// <summary>
/// Generate seal bitmap
/// </summary>
/// <returns></returns>
public Bitmap TextOnPathBitmap()
{
// Create bitmap and graphics
Bitmap bit = new Bitmap( _rect.Width, _rect.Height );
Graphics g = Graphics.FromImage( bit );
// Compute string length in graphics
float[] fCharWidth = new float[_text.Length];
float fTotalWidth = ComputeStringLength( _text, g, fCharWidth,
_letterspace, _chardirect );
// Compute arc's start-angle and end-angle
double fStartAngle, fSweepAngle;
fSweepAngle = fTotalWidth * 360 / ( _rectcircle.Width * Math.PI );
fStartAngle = 270 - fSweepAngle / 2;
// Compute every character's position and angle
PointF[] pntChars = new PointF[ _text.Length ];
double[] fCharAngle = new double[ _text.Length ];
ComputeCharPos( fCharWidth, pntChars, fCharAngle, fStartAngle );
g.SmoothingMode = SmoothingMode.HighQuality;
g.CompositingQuality = CompositingQuality.HighQuality;
g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;
DrawSealBase( g );
// Draw every character
for( int i = 0; i < _text.Length; i++ )
DrawRotatedText( g, _text[i].ToString(), (float)(fCharAngle[i] + _degree), pntChars[i] );
g.Dispose();
// Return bitmap
return bit;
}
/// <summary>
/// Draw seal base
/// </summary>
/// <param name="g"></param>
private void DrawSealBase( Graphics g )
{
// Draw background
g.FillRectangle( Brushes.Black, _rect );
g.FillEllipse( new SolidBrush( _fillcolor ),
new Rectangle( 1,1, _rect.Width - 2, _rect.Height - 2 ) );
g.FillEllipse( Brushes.White,
new Rectangle( 4, 4, _rect.Width - 8, _rect.Height - 8 ) );
// Draw start signal
StringFormat sf = new StringFormat();
string strStar = "★";
Font fnt = new Font( _font.FontFamily, _font.Size * 3 );
sf.Alignment = StringAlignment.Center;
sf.LineAlignment = StringAlignment.Center;
SizeF siz = g.MeasureString( strStar, fnt );
g.DrawString( strStar, fnt, new SolidBrush( _fillcolor ),
new RectangleF( _rect.Width / 2 - siz.Width / 2,
_rect.Height / 2 - siz.Height/ 2,
siz.Width, siz.Height ), sf );
// Draw base string
float[] fCharWidth = new float[_basestring.Length];
float fTotalWidths = ComputeStringLength( _basestring, g, fCharWidth, 0,
Char_Direction.Center );
float fLeftPos = ( _rect.Width - fTotalWidths ) / 2;
PointF pt;
for( int i = 0; i < _basestring.Length; i++ )
{
pt = new PointF( fLeftPos + fCharWidth[i] / 2,
_rect.Height / 2 + siz.Height / 2 + 10 );
DrawRotatedText( g, _basestring[i].ToString(), 0, pt );
fLeftPos += fCharWidth[i];
}
}
/// <summary>
/// Draw every rotated character
/// </summary>
/// <param name="g"></param>
/// <param name="_text"></param>
/// <param name="_angle"></param>
/// <param name="_PointCenter"></param>
private void DrawRotatedText( Graphics g, string _text, float _angle, PointF _PointCenter )
{
// Init format
StringFormat sf = new StringFormat();
sf.Alignment = StringAlignment.Center;
sf.LineAlignment = StringAlignment.Center;
// Create graphics path
GraphicsPath gp = new GraphicsPath( System.Drawing.Drawing2D.FillMode.Winding );
int x = (int)_PointCenter.X;
int y = (int)_PointCenter.Y;
// Add string
gp.AddString( _text, _font.FontFamily, (int)_font.Style,
_font.Size, new Point( x, y ), sf );
// Rotate string and draw it
Matrix m = new Matrix();
m.RotateAt( _angle, new PointF( x,y ) );
g.Transform = m;
g.DrawPath( new Pen( _color), gp );
g.FillPath( new SolidBrush( _fillcolor ), gp );
}
}
public enum Char_Direction
{
Center = 0,
OutSide = 1,
ClockWise = 2,
AntiClockWise = 3,
}
}
