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Posted 20 Apr 2006

Text on Path with VB.NET

, 2 May 2006
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A VB.NET class for drawing text on a path.

Introduction

I searched the internet for a long time for some algorithm to display a "Text on a Path", but I only fond the Batik SVG Toolkit. It's a Java project for displaying SVG. SVG has the ability to display "Text on a Path", but I only needed the Text on Path functionality.

So, I started recollecting my old math education, and coded the first lines to calculate the angle of defined position on a path.

Do you remember a²+b²=c²? That is the base to solve this problem. You need two points on a straight line.

<IMG height=260 alt=a²+b²=c² src="/KB/GDI-plus/Text_on_Path_with_VBNET/pytho.jpg" width=160>

Private Function GetAngle(ByVal _point1 As PointF, _
ByVal _point2 As PointF) As Decimal
Dim c As Decimal
c = Math.Sqrt((_point2.X - _point1.X) ^ 2 + _
(_point2.Y - _point1.Y) ^ 2)
'Oh yeah good old math a²+b²=c²

If c = 0 Then
Return 0
End If 'We must change the side where the triangle is
If _point1.X > _point2.X Then
Return Math.Asin((_point1.Y - _point2.Y) / c) * _
180 / Math.PI - 180
Else
Return Math.Asin((_point2.Y - _point1.Y) / c) * _
180 / Math.PI
End If

End Function

Using the code

You can use the TextOnPath class to get a bitmap with the text on the given path.

The path must be set as PathData. You can also the the TextPathPosition (Under, Center, Above) and the align the text (Left, Center, Right).

Dim _points(5) As PointF
Dim _top As TextOnPath.TextOnPath = New TextOnPath.TextOnPath
Dim _gp As GraphicsPath = New GraphicsPath

_points(0) = New PointF(81, 183)
_points(1) = New PointF(321, 305)
_points(2) = New PointF(333, 622)
_points(3) = New PointF(854, 632)
_points(4) = New PointF(864, 153)
_points(5) = New PointF(562, 224)

_top.PathDataTOP = _gp.PathData
_top.FontTOP = New Font("Microsoft Sans Serif", _
36, FontStyle.Regular)
_top.FillColorTOP = Color.Black
_top.ColorTOP = Color.White
_top.TextTOP = "Text on path goes around a path"
_top.ShowPath = True
_top.PathAlignTOP = TextOnPath.PathAlign.Center
_top.LetterSpacePercentage = 100
_top.TextPathPosition = TextOnPath.TextPosition.CenterPath

Dim oBitmap as Bitmap
oBitmap = _top.TextOnPathBitmap

You can also get the new path data as an SVG string, so you can use it in HTML with Adobe SVG Viewer, or in Corel Draw or Adobe Illustrator.

Dim _svg As String
_svg = _top.GetSVG(1024, 768)

Points of interest

If someone has ideas to optimize this code, please contact me, and sorry for the bad English and the short description. This is my first article, and I'm still learning.

History

• Version 1.0 released.
• Version 1.01 released (PathPoint calculation optimized).

A list of licenses authors might use can be found here

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