How do replicate "RenderSurfaceWithinCorners" in my matrix calculation?

[tmighty2]

I would like to include an image perspective warping option in my existing matrix calculation ("DrawTo", stated at the end of this post).
A great example using RenderSurfaceWithinCorners is in this thread.

My problem is that I can not use RenderSurfaceWithinCorners, and I am looking for a way to transform a matrix (which I use to render an image using RC6) so that the image is render as if I was using RenderSurfaceWithinCorners.

The reason I can't utilize RenderSurfaceWithinCorners is that I need to maintain image centering while compensating for x and y offsets + scaling + rotating. Therefore, I'm seeking an alternative way to transform a matrix that I use with RC6 to render images similarly to how RenderSurfaceWithinCorners would.

How could I replicate such a perspective warping in the my "DrawTo" function?



This is the code that would do what I want (but which I can not use):

Private Sub DrawRotated(Ang As Double, ByVal PerspectiveFactor As Double)
    Dim DeltaX    As Double
    Dim DeltaY    As Double
    Dim CenterX#
    Dim X1#, Y1#, X2#, Y2#
    Dim X3#, Y3#, X4#, Y4#

    Const kDeformY As Double = 55

    DeltaX = TargetWidth * 0.5 * Cos(-Ang * 3.14159265358979)
    DeltaY = kDeformY * Sin(-Ang * 3.14159265358979) * PerspectiveFactor

    CenterX = PIC.ScaleWidth * 0.5
    X1 = CenterX + DeltaX
    Y1 = kDeformY + DeltaY
    X2 = CenterX - DeltaX
    Y2 = kDeformY - DeltaY
    X3 = X2
    Y3 = TargetHeight - kDeformY + DeltaY
    X4 = X1
    Y4 = TargetHeight - kDeformY - DeltaY

    If Sgn(DeltaX) <> Sgn(OldDX) Then
        If CurrImg = "IMG1" Then CurrImg = "IMG2" Else: CurrImg = "IMG1"
        OldDX = DeltaX
    End If

    CC.SetSourceColor 0: CC.Paint
    CC.RenderSurfaceWithinCorners CurrImg, X1, Y1, X2, Y2, X3, Y3, X4, Y4

    Srf.DrawToDC PIC.hDC
    DoEvents
End Sub

Public Function DrawTo(ByRef uDestCC As cCairoContext, ByVal uLeft As Long, ByVal uTop As Long) As Boolean

    If m_Img Is Nothing Then
        Exit Function
    End If

    Dim dblOffx As Double: Dim dblOffy As Double
    
    Dim dblNewWidth As Double
    Dim dblNewHeight As Double
    dblNewWidth = (m_Img.Width * Me.ScaleFactorWidth)
    dblNewHeight = (m_Img.Height * Me.ScaleFactorHeight)

    
    If (dblNewWidth = 0) Or (dblNewHeight = 0) Or (m_dblAlpha < 0.05) Then
        Exit Function
    End If
    
   uDestCC.Save
        ' Calculate offsets based on alignment and scaling
        dblOffx = Me.AlignmentFactorX * (dblNewWidth / 2)
        dblOffy = Me.AlignmentFactorY * (dblNewHeight / 2)
        
        Dim dblNewX1 As Double:   Dim dblNewY1 As Double
        dblNewX1 = (uLeft + dblOffx)
        dblNewY1 = (uTop + dblOffy)
        
        Dim dblNewX2 As Double: Dim dblNewY2 As Double
        dblNewX2 = -(m_Img.Width / 2) - (Me.CenterOffsetX / 2)
        dblNewY2 = -(m_Img.Height / 2) - (Me.CenterOffsetY / 2)



        m_Matrix.TranslateCoords dblNewX1, dblNewY1
        m_Matrix.RotateCoordsDeg m_sngAngleDeg
        m_Matrix.SkewXDeg m_dblPerspectiveFactor * Me.ScaleFactorWidth
        m_Matrix.ScaleCoords Me.ScaleFactorWidth, Me.ScaleFactorHeight
        m_Matrix.TranslateCoords dblNewX2, dblNewY2

        ' Set the final transformation
        Set uDestCC.Matrix = m_Matrix
        
        ' Now draw the image with the same transformations
         uDestCC.RenderSurfaceContent m_Img, 0, 0, , , , m_dblAlpha
    
        Dim corners(3) As POINT  ' Array of points for 4 corners
        'Define rectangle corners using the "m_Img" surface dimensions
        corners(0).x = 0: corners(0).y = 0  ' Top Left
        corners(1).x = m_Img.Width: corners(1).y = 0 ' Top right
        corners(2).x = 0: corners(2).y = m_Img.Height ' Bottom left
        corners(3).x = m_Img.Width: corners(3).y = m_Img.Height ' Bottom right
    
        ' Transform each corner point
        Dim i As Integer
        For i = 0 To 3
            m_Matrix.CalculatePoint corners(i).x, corners(i).y
        Next
        
        'Determine the render rect
        Dim cornerTopLeft As POINT
        Dim cornerBottomRight As POINT
      
        'Start with "invalid" values
        cornerTopLeft.x = 999999
        cornerTopLeft.y = 999999
        cornerBottomRight.x = -999999
        cornerBottomRight.y = -999999
    
        For i = 0 To 3
            Dim n As POINT
            n = corners(i)
            
            'Search minimum "x" for TopLeft
            If n.x < cornerTopLeft.x Then
                cornerTopLeft.x = n.x
            End If
            
            'Search minimum "y" for TopLeft
            If n.y < cornerTopLeft.y Then
                cornerTopLeft.y = n.y
            End If
            
            'Search maximum "x" for BottomRight
            If n.x > cornerBottomRight.x Then
                cornerBottomRight.x = n.x
            End If
            
            'Search maximum "y" for BottomRight
            If n.y > cornerBottomRight.y Then
                cornerBottomRight.y = n.y
            End If
        Next
    
        'store the render corners
        m_TopX = cornerTopLeft.x
        m_TopY = cornerTopLeft.y
       
        m_BottomX = cornerBottomRight.x
        m_BottomY = cornerBottomRight.y

        ' Clear the path
        uDestCC.ClearPath False

        m_Matrix.ResetToIdentity

    uDestCC.Restore

    DrawTo = True

End Function