Building a Stroke Class to outline your images via GDI+
I won’t prattle on. The aim was to find a way to transform this image:
Into this image (done in GIMP):
All this within the restraints of a winforms app for .NET framework 3.5 (don’t ask..).
I found this excellent answer on StackOverflow. I amalgamated this with a few other techniques (the main one being a fast blurring class to provide the option of blurred edges to the stroke – to essentially produce Glow) and got things working. The answer does depend on a SuperFastBlur alghorithm (see here) which was written in C#. I couldn’t be bothered to convert it to VB.net, so I just compiled it into a library and included it in my project.
Then, you simply include the Classes at the bottom of this page (I just saved the all to a single file). To apply a Stroke to your image, you then just use:
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Dim stroke As New Stroke _image = stroke.Apply(_image, _strokeWidth, _strokeColor, _strokeBlur, _strokeLineJoin) |
_image is either Image or Bitmap and the other parameters should be self explanatory. Here are some results:
And some unexpected funky effects by changing LineJoin:
Not perfect, but not bad for GDI+?
The code:
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Imports System.Drawing Imports System.Drawing.Drawing2D Imports System.Drawing.Imaging Imports System.Runtime.InteropServices Imports SuperfastBlur Public Class Stroke Private stride As Integer = 0 Private visited As Integer() = Nothing Private bytes As Byte() = Nothing Private borderdata As PointData = Nothing Private size As Size = Size.Empty Private outside As Boolean = False Private zeropoint As Point = New Point(-1, -1) Public Function Apply(bmp As Bitmap, strokeWidth As Integer, strokeColor As Color, strokeBlur As Integer, LineJoin As LineJoin) As Bitmap Dim borderedBmp As Bitmap = NewBitmapWithBorder(bmp, strokeWidth) Dim imgPointsArray As List(Of Point()) = Find(borderedBmp) Dim newBmp As Bitmap = New Bitmap(borderedBmp.Width, borderedBmp.Height) Using g As Graphics = Graphics.FromImage(newBmp) With g .PixelOffsetMode = PixelOffsetMode.HighQuality .CompositingMode = CompositingMode.SourceOver .InterpolationMode = InterpolationMode.HighQualityBilinear .SmoothingMode = SmoothingMode.AntiAlias .CompositingQuality = CompositingQuality.HighQuality End With For Each pointsArray As Point() In imgPointsArray DrawOutline(g, pointsArray, strokeColor, strokeWidth, LineCap.Round, LineJoin) Next End Using If strokeBlur > 0 Then Dim gblur = New GaussianBlur(newBmp) newBmp = gblur.Process(strokeBlur) End If Using g As Graphics = Graphics.FromImage(newBmp) g.DrawImage(borderedBmp, 0, 0) End Using Return newBmp End Function Private Sub DrawOutline(g As Graphics, points As Point(), penColor As Color, penSize As Single, cap As LineCap, lJoin As LineJoin) Using gp As GraphicsPath = New GraphicsPath(FillMode.Winding), pen As New Pen(penColor, penSize) With {.LineJoin = lJoin, .StartCap = cap, .EndCap = cap}, widenPen As New Pen(penColor, 1.0F) gp.AddCurve(points) gp.Widen(widenPen) g.DrawPath(pen, gp) End Using End Sub Private Function NewBitmapWithBorder(ByVal bmp As Bitmap, ByVal Optional borderSize As Integer = 0) As Bitmap Dim newWidth As Integer = bmp.Width + (borderSize * 2) Dim newHeight As Integer = bmp.Height + (borderSize * 2) Dim newImage As Image = New Bitmap(newWidth, newHeight) Using gfx As Graphics = Graphics.FromImage(newImage) Using border As Brush = New SolidBrush(Color.Transparent) ' gfx.FillRectangle(border, 0, 0, newWidth, newHeight) End Using gfx.DrawImage(bmp, New Rectangle(borderSize, borderSize, bmp.Width, bmp.Height)) End Using Return CType(newImage, Bitmap) End Function Public Function Find(ByVal bmp As Bitmap, ByVal Optional outside As Boolean = True) As List(Of Point()) Me.outside = outside Dim border As List(Of Point) = New List(Of Point)() Dim bmpdata As BitmapData = bmp.LockBits(New Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.[ReadOnly], PixelFormat.Format32bppArgb) stride = bmpdata.Stride bytes = New Byte(bmp.Width * bmp.Height * 4 - 1) {} size = bmp.Size Marshal.Copy(bmpdata.Scan0, bytes, 0, bytes.Length) borderdata = getBorderData(bytes) bmp.UnlockBits(bmpdata) Dim regions As List(Of List(Of Point)) = New List(Of List(Of Point))() While borderdata.PointCount > 0 Dim region As List(Of Point) = New List(Of Point)() Dim valid As Boolean = True Dim startpos As Point = getFirstPoint(borderdata) visited = New Integer(bmp.Size.Width * bmp.Size.Height - 1) {} region.Add(startpos) Dim current As Point = getNextPoint(startpos) If current <> zeropoint Then visited(current.Y * bmp.Width + current.X) += 1 region.Add(current) End If If current = zeropoint Then valid = False While Not current.Equals(startpos) AndAlso valid Dim pos = current If visited(current.Y * bmp.Width + current.X) < 2 Then current = getNextPoint(pos) visited(pos.Y * bmp.Width + pos.X) += 1 If current = zeropoint Then current = getNextPointBackwards(pos) Else current = getNextPointBackwards(pos) End If If current = zeropoint Then valid = False Exit While End If visited(current.Y * bmp.Width + current.X) += 1 region.Add(current) End While For Each p In region borderdata.SetPoint(p.Y * bmp.Width + p.X, False) Next If valid Then regions.Add(region) End While For Each region In regions Dim duplicatedpos As Integer = -1 Dim duplicatecheck As Boolean() = New Boolean(size.Width * size.Height - 1) {} Dim length As Integer = region.Count For i As Integer = 0 To length - 1 Dim p = region(i) If duplicatecheck(p.Y * size.Width + p.X) Then duplicatedpos = i - 1 Exit For End If duplicatecheck(p.Y * size.Width + p.X) = True Next If duplicatedpos = -1 Then Continue For If duplicatedpos <> ((region.Count - 1) / 2) Then Continue For Dim reversed As Boolean = True For i As Integer = 0 To duplicatedpos - 1 If region(duplicatedpos - i - 1) <> region(duplicatedpos + i + 1) Then reversed = False Exit For End If Next If Not reversed Then Continue For region.RemoveRange(duplicatedpos + 1, region.Count - duplicatedpos - 1) Next Dim tempregions As List(Of List(Of Point)) = New List(Of List(Of Point))(regions) regions.Clear() Dim connected As Boolean = True While connected connected = False For Each region In tempregions Dim connectionpos As Integer = -1 Dim connectionregion As Integer = -1 Dim pointstart As Point = region.First() Dim pointend As Point = region.Last() For ir As Integer = 0 To regions.Count - 1 Dim otherregion = regions(ir) If region Is otherregion Then Continue For For ip As Integer = 0 To otherregion.Count - 1 Dim p = otherregion(ip) If (isConnected(pointstart, p) AndAlso isConnected(pointend, p)) OrElse (isConnected(pointstart, p) AndAlso isConnected(pointstart, p)) Then connectionregion = ir connectionpos = ip End If If (isConnected(pointend, p) AndAlso isConnected(pointend, p)) Then region.Reverse() connectionregion = ir connectionpos = ip End If Next Next If connectionpos = -1 Then regions.Add(region) Else regions(connectionregion).InsertRange(connectionpos, region) End If Next tempregions = New List(Of List(Of Point))(regions) regions.Clear() End While Dim returnregions As List(Of Point()) = New List(Of Point())() For Each region In tempregions returnregions.Add(region.ToArray()) Next Return returnregions End Function Private Function isConnected(ByVal p0 As Point, ByVal p1 As Point) As Boolean If p0.X = p1.X AndAlso p0.Y - 1 = p1.Y Then Return True If p0.X + 1 = p1.X AndAlso p0.Y - 1 = p1.Y Then Return True If p0.X + 1 = p1.X AndAlso p0.Y = p1.Y Then Return True If p0.X + 1 = p1.X AndAlso p0.Y + 1 = p1.Y Then Return True If p0.X = p1.X AndAlso p0.Y + 1 = p1.Y Then Return True If p0.X - 1 = p1.X AndAlso p0.Y + 1 = p1.Y Then Return True If p0.X - 1 = p1.X AndAlso p0.Y = p1.Y Then Return True If p0.X - 1 = p1.X AndAlso p0.Y - 1 = p1.Y Then Return True Return False End Function Private Function getNextPoint(ByVal pos As Point) As Point If pos.Y > 0 Then Dim x As Integer = pos.X Dim y As Integer = pos.Y - 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If End If End If If pos.Y > 0 AndAlso pos.X < size.Width - 1 Then Dim x As Integer = pos.X + 1 Dim y As Integer = pos.Y - 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If End If End If If pos.X < size.Width - 1 Then Dim x As Integer = pos.X + 1 Dim y As Integer = pos.Y If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If End If End If If pos.X < size.Width - 1 AndAlso pos.Y < size.Height - 1 Then Dim x As Integer = pos.X + 1 Dim y As Integer = pos.Y + 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If End If End If If pos.Y < size.Height - 1 Then Dim x As Integer = pos.X Dim y As Integer = pos.Y + 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If End If End If If pos.Y < size.Height - 1 AndAlso pos.X > 0 Then Dim x As Integer = pos.X - 1 Dim y As Integer = pos.Y + 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If End If End If If pos.X > 0 Then Dim x As Integer = pos.X - 1 Dim y As Integer = pos.Y If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If End If End If If pos.X > 0 AndAlso pos.Y > 0 Then Dim x As Integer = pos.X - 1 Dim y As Integer = pos.Y - 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If End If End If Return zeropoint End Function Private Function getNextPointBackwards(ByVal pos As Point) As Point Dim backpoint As Point = zeropoint Dim trys As Integer = 0 If pos.X > 0 AndAlso pos.Y > 0 Then Dim x As Integer = pos.X - 1 Dim y As Integer = pos.Y - 1 If ValidPoint(x, y) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If If backpoint = zeropoint OrElse trys > visited(y * size.Width + x) Then backpoint = New Point(x, y) trys = visited(y * size.Width + x) End If End If End If If pos.X > 0 Then Dim x As Integer = pos.X - 1 Dim y As Integer = pos.Y If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If If backpoint = zeropoint OrElse trys > visited(y * size.Width + x) Then backpoint = New Point(x, y) trys = visited(y * size.Width + x) End If End If End If If pos.Y < size.Height - 1 AndAlso pos.X > 0 Then Dim x As Integer = pos.X - 1 Dim y As Integer = pos.Y + 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If If backpoint = zeropoint OrElse trys > visited(y * size.Width + x) Then backpoint = New Point(x, y) trys = visited(y * size.Width + x) End If End If End If If pos.Y < size.Height - 1 Then Dim x As Integer = pos.X Dim y As Integer = pos.Y + 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If If backpoint = zeropoint OrElse trys > visited(y * size.Width + x) Then backpoint = New Point(x, y) trys = visited(y * size.Width + x) End If End If End If If pos.X < size.Width - 1 AndAlso pos.Y < size.Height - 1 Then Dim x As Integer = pos.X + 1 Dim y As Integer = pos.Y + 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If If backpoint = zeropoint OrElse trys > visited(y * size.Width + x) Then backpoint = New Point(x, y) trys = visited(y * size.Width + x) End If End If End If If pos.X < size.Width - 1 Then Dim x As Integer = pos.X + 1 Dim y As Integer = pos.Y If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If If backpoint = zeropoint OrElse trys > visited(y * size.Width + x) Then backpoint = New Point(x, y) trys = visited(y * size.Width + x) End If End If End If If pos.Y > 0 AndAlso pos.X < size.Width - 1 Then Dim x As Integer = pos.X + 1 Dim y As Integer = pos.Y - 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If If backpoint = zeropoint OrElse trys > visited(y * size.Width + x) Then backpoint = New Point(x, y) trys = visited(y * size.Width + x) End If End If End If If pos.Y > 0 Then Dim x As Integer = pos.X Dim y As Integer = pos.Y - 1 If (ValidPoint(x, y)) AndAlso HasNeighbor(x, y) Then If visited(y * size.Width + x) = 0 Then Return New Point(x, y) End If If backpoint = zeropoint OrElse trys > visited(y * size.Width + x) Then backpoint = New Point(x, y) trys = visited(y * size.Width + x) End If End If End If Return backpoint End Function Private Function ValidPoint(ByVal x As Integer, ByVal y As Integer) As Boolean Return (borderdata(y * size.Width + x)) End Function Private Function HasNeighbor(ByVal x As Integer, ByVal y As Integer) As Boolean If y > 0 Then If Not borderdata((y - 1) * size.Width + x) Then Return True End If ElseIf ValidPoint(x, y) Then Return True End If If x < size.Width - 1 Then If Not borderdata(y * size.Width + (x + 1)) Then Return True End If ElseIf ValidPoint(x, y) Then Return True End If If y < size.Height - 1 Then If Not borderdata((y + 1) * size.Width + x) Then Return True End If ElseIf ValidPoint(x, y) Then Return True End If If x > 0 Then If Not borderdata(y * size.Width + (x - 1)) Then Return True End If ElseIf ValidPoint(x, y) Then Return True End If Return False End Function Private Function getFirstPoint(ByVal data As PointData) As Point Dim startpos As Point = zeropoint For y As Integer = 0 To size.Height - 1 For x As Integer = 0 To size.Width - 1 If data(y * size.Width + x) Then startpos = New Point(x, y) Return startpos End If Next Next Return startpos End Function Private Function getBorderData(ByVal bytes As Byte()) As PointData Dim isborderpoint As PointData = New PointData(size.Height * size.Width) Dim prevtrans As Boolean = False Dim currenttrans As Boolean = False For y As Integer = 0 To size.Height - 1 prevtrans = False For x As Integer = 0 To size.Width If x = size.Width Then If Not prevtrans Then isborderpoint.SetPoint(y * size.Width + x - 1, True) End If Continue For End If currenttrans = bytes(y * stride + x * 4 + 3) = 0 If x = 0 AndAlso Not currenttrans Then isborderpoint.SetPoint(y * size.Width + x, True) If prevtrans AndAlso Not currenttrans Then isborderpoint.SetPoint(y * size.Width + x - 1, True) If Not prevtrans AndAlso currenttrans AndAlso x <> 0 Then isborderpoint.SetPoint(y * size.Width + x, True) prevtrans = currenttrans Next Next For x As Integer = 0 To size.Width - 1 prevtrans = False For y As Integer = 0 To size.Height If y = size.Height Then If Not prevtrans Then isborderpoint.SetPoint((y - 1) * size.Width + x, True) End If Continue For End If currenttrans = bytes(y * stride + x * 4 + 3) = 0 If y = 0 AndAlso Not currenttrans Then isborderpoint.SetPoint(y * size.Width + x, True) If prevtrans AndAlso Not currenttrans Then isborderpoint.SetPoint((y - 1) * size.Width + x, True) If Not prevtrans AndAlso currenttrans AndAlso y <> 0 Then isborderpoint.SetPoint(y * size.Width + x, True) prevtrans = currenttrans Next Next Return isborderpoint End Function End Class Class PointData Private points As Boolean() = Nothing Private validpoints As Integer = 0 Public Sub New(ByVal length As Integer) points = New Boolean(length - 1) {} End Sub Public ReadOnly Property PointCount As Integer Get Return validpoints End Get End Property Public Sub SetPoint(ByVal pos As Integer, ByVal state As Boolean) If points(pos) <> state Then If state Then validpoints += 1 Else validpoints -= 1 End If End If points(pos) = state End Sub Default Public ReadOnly Property Item(ByVal pos As Integer) As Boolean Get Return points(pos) End Get End Property End Class |
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