製作印章來說，主要是如何讓字均勻的顯示在弧線段上，那麼一般的印章要麼以圓或者橢圓爲底圖，不過這兩者的算法大致相同，爲了方便說明，如下就用相對簡單的圓來舉例說明，如果需要做橢圓的話，可以在我的基礎上進行擴展，因爲核心算法是一樣的，相對於圓來說，橢圓求弧長以及各個字符的位置，這兩點相對麻煩些，但是這兩者都可找到相應的數學公式。

這裏首先提一點，我這篇文章部分借鑑了codeproject的一個例子，原文可以參看如下地址。

http://www.codeproject.com/vb/net/Text_on_Path_with_VBNET.asp

（說實話，這篇文章寫得有些亂，而且對於buffer的操作近乎於瘋狂）

由於印章的實現相對於這篇文章來說，相對簡單多了，而且規律性很強，因此我自己考慮重新組織算法進行實現。

那麼實現一個印章，大致步驟如下。

1．計算字符串總長度，以及各個字符的長度；

2．計算出字符串的起始角度；

3．求出每個字符的所在的點，以及相對於中心的角度；

4．繪製每個字符。

計算字符串總長度，以及各個字符的長度

這裏需要用到“Graphics.MeasureString”和“Graphics.MeasureCharacterRanges”這兩個方法，由於前者算出來的總長度有問題，所以需要後面進行重新計算（此外，這裏我還考慮了字符最後顯示方向）。

這部分的代碼如下：

/// <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;

}

計算出字符串的起始角度

爲了更好地開展文章，那麼首先說說在我這篇文章中，座標的度數位置。詳情參看如下圖示。

對於圖形角度分佈有個概念後，那麼對於整個字符串所跨的弧度以及起始弧度的計算，就相對比較簡單了。具體如下：

// Compute arc's start-angle and end-angle

double fStartAngle, fSweepAngle;

fSweepAngle = fTotalWidth * 360 / ( _rectcircle.Width * Math.PI );

fStartAngle = 270 - fSweepAngle / 2;

求出每個字符的所在的點，以及相對於中心的角度

這一部分相對要麻煩些，大致步驟如下。

1．通過字符長度，求出字符所跨的弧度；

2．根據字符所跨的弧度，以及字符起始位置，算出字符的中心位置所對應的角度；

3．由於相對中心的角度已知，根據三角公式很容易算出字符所在弧上的點，如下圖所示；

4．根據字符長度以及間隔距離，算出下一個字符的起始角度；

5．重複1直至整個字符串結束。

那麼這部分的具體代碼如下。

/// <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;

}

繪製每個字符

由於每個字符所在的點以及相對於圓心的角度都已經計算出來，那麼進行繪製就相對簡單多了，這裏只是通過Matrix來轉換一下座標而已。

具體代碼如下。

/// <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 );

}

以上就是繪製印章的核心算法。對於這個類的調用，如下即可。

TextOnSeal _top = new TextOnSeal();

_top.TextFont = new Font("宋體", 16, FontStyle.Regular);

_top.FillColor = Color.Red;

_top.ColorTOP = Color.Black;

_top.Text = "中華人民共和國";

_top.BaseString = "愚翁專用章";

_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 );

通過如上的代碼，可以得到如下的效果。

其實如果做印章來說，還有很多地方需要細化，那麼如果網友對此有興趣，可以在我的基礎上進行擴展，在此我就不一一述說。

如下是整個類的完整代碼。

//--------------------------- 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,

}

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