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Get translation, rotation, scale and shear out of a System.Drawing.Drawing2d.Matrix affine transformation

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  1. Imports System.Drawing, System.Drawing.Drawing2D
  2.  
  3. Public Class Affine
  4.     Dim mat As Matrix
  5.     ''' <summary>
  6.     ''' X value of translation vector.
  7.     ''' </summary>
  8.     ''' <value></value>
  9.     ''' <returns></returns>
  10.     ''' <remarks></remarks>
  11.     Public ReadOnly Property offsetx() As Single
  12.         Get
  13.             Return mat.OffsetX
  14.         End Get
  15.     End Property
  16.     ''' <summary>
  17.     ''' Y value of translation vector.
  18.     ''' </summary>
  19.     ''' <value></value>
  20.     ''' <returns></returns>
  21.     ''' <remarks></remarks>
  22.     Public ReadOnly Property offsety() As Single
  23.         Get
  24.             Return mat.OffsetY
  25.         End Get
  26.     End Property
  27.  
  28.     ''' <summary>
  29.     ''' rotation in degrees, clockwise = positive
  30.     ''' </summary>
  31.     ''' <remarks></remarks>
  32.     Public rot As Single
  33.  
  34.     ''' <summary>
  35.     ''' x and y values of scale vector
  36.     ''' </summary>
  37.     ''' <remarks></remarks>
  38.     Public scalex, scaley As Single
  39.     ''' <summary>
  40.     ''' x and y values of shear vector
  41.     ''' </summary>
  42.     ''' <remarks></remarks>
  43.     Public shearx, sheary As Single
  44.  
  45.     ''' <summary>
  46.     ''' Construct a new Affine from the given Drawing2d.Matrix
  47.     ''' </summary>
  48.     ''' <param name="m"></param>
  49.     ''' <remarks></remarks>
  50.     Sub New(ByVal m As Matrix)
  51.         mat = m
  52.         Decompose()
  53.     End Sub
  54.  
  55.     ''' <summary>
  56.     ''' Create a new Affine with default values (corresponding to identity matrix)
  57.     ''' </summary>
  58.     ''' <remarks></remarks>
  59.     Sub New()
  60.         mat = New matrix
  61.         rot = 0
  62.         scalex = 1
  63.         scaley = 1
  64.         shearx = 0
  65.         sheary = 0
  66.     End Sub
  67.  
  68.     ''' <summary>
  69.     ''' Decompose our matrix
  70.     ''' </summary>
  71.     ''' <remarks></remarks>
  72.     Private Sub Decompose()
  73.  
  74.         ' the original matrix
  75.         Dim m0 As Matrix = mat
  76.  
  77.         ' remove translation
  78.         Dim m1 As New Matrix
  79.         m1.Multiply(m0)
  80.         m1.Translate(-m0.OffsetX, -m0.OffsetY)
  81.  
  82.         ' get rotation
  83.         Dim pts(1) As PointF
  84.         pts(0) = New PointF(0, 0)
  85.         pts(1) = New PointF(1, 0)
  86.         m1.TransformPoints(pts)
  87.         rot = Math.Atan2( _
  88.             pts(1).Y - pts(0).Y, _
  89.             pts(1).X - pts(0).X) * 180.0 / Math.PI
  90.  
  91.         ' get scale and shear
  92.         pts(0) = New PointF(0, 0)
  93.         pts(1) = New PointF(1, 1)
  94.         Dim m2 As New Matrix
  95.         m2.Rotate(-rot)
  96.         m2.Multiply(mat)
  97.         m2.TransformPoints(pts)
  98.  
  99.         scalex = pts(1).X - pts(0).X
  100.         scaley = pts(1).Y - pts(0).Y
  101.  
  102.         ' get shear
  103.         shearx = pts(1).X - 1.0
  104.         sheary = pts(1).Y - 1.0
  105.  
  106.     End Sub
  107.  
  108.     'Sub test()
  109.     '    Dim m As New Matrix
  110.     '    Dim a As New Affine(m)
  111.     '    Assert.AreEqual(0.0, a.rot)
  112.     '    Assert.AreEqual(1.0, a.scalex)
  113.     '    Assert.AreEqual(1.0, a.scaley)
  114.     '    Assert.AreEqual(0.0, a.shearx)
  115.     '    Assert.AreEqual(0.0, a.sheary)
  116.  
  117.     '    m.Rotate(45)
  118.     '    m.Scale(2, 3)
  119.     '    a = New Affine(m)
  120.     '    Assert.AreEqual(45.0, a.rot)
  121.     '    Assert.Less(Math.Abs(2.0 - a.scalex), 0.001)
  122.     '    Assert.Less(Math.Abs(3.0 - a.scaley), 0.001)
  123.  
  124.     'End Sub
  125. End Class

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