使用PathGeometry.Widen（）时，带有StrokeStyle的不需要的尾盖

我使用SharpDX以便在.NET WinForms上绘制折线。这些折线代表钣金的轮廓。

组成PathGeometry对象，定义了折线：

'reset m_pathGeometry (the core geometry of this sheetmetal profile)
m_pathGeometry = New PathGeometry(D2DCanvas.canvas_factory2D)

' pointsRef = collection of points showing the segments & bends in this sheetmetal profile
Dim pointsRef As List(Of Vector2) = calculateSegmentsPoints()

' Add lines to m_pathGeometry using our points collection
Using sink As SimplifiedGeometrySink = m_pathGeometry.Open()
    sink.BeginFigure(pointsRef.First(), FigureBegin.Filled)
    sink.AddLines(pointsRef.ToArray)
    sink.EndFigure(FigureEnd.Open)
    sink.Close()
End Using

在绘制到屏幕上之前，我应用了一个变换（以考虑到变换和缩放）：

' update m_fillTransformedGeometry based on m_pathGeometry & the current transform matrix3x2,
m_fillTransformedGeometry = New TransformedGeometry(D2DCanvas.canvas_factory2D, m_pathGeometry, Matrix3x2.Rotation(m_rotation, InsertPoint) * _transformMatrix)

' to draw the polyline
D2DCanvas.canvas_renderTarget2D.DrawGeometry(m_fillTransformedGeometry, m_fillBrush, plaatdikte * _transformMatrix.ScaleVector(1), m_strokeStyle)

折线以笔触样式绘制，圆角线连接和扁平端盖

With m_strokeStyleProps
   .LineJoin = LineJoin.Round
   .EndCap = CapStyle.Flat
   .StartCap = CapStyle.Flat
End With

结果有点苍白，可以用中风：

第一个想法是用更深的颜色绘制同一条折线，但StrokeWidth稍微宽一些：

' First draw a wider stroke
D2DCanvas.canvas_renderTarget2D.DrawGeometry(m_fillTransformedGeometry, m_strokeBrush, (plaatdikte + 0.2) * _transformMatrix.ScaleVector(1), m_strokeStyle)

' Then draw the fill
D2DCanvas.canvas_renderTarget2D.DrawGeometry(m_fillTransformedGeometry, m_fillBrush, plaatdikte * _transformMatrix.ScaleVector(1), m_strokeStyle)

结果不错，但这种方式的端盖不会碰到：

Second idea is to create a (slightly widened) PathGeometry for the stroke itself by calling the Widen() method on the original polyline-PathGeometry.

'define m_widenedPathGeometry (makes op the outline/stroke of this sheetmetal profile)
m_widenedPathGeometry = New PathGeometry(D2DCanvas.canvas_factory2D)
Using sink As SimplifiedGeometrySink = m_widenedPathGeometry.Open()
    m_pathGeometry.Widen(0.2, sink)
    sink.Close()
End Using

This widened geometry gets drawn (taking in account transformation) as a 'stroke' prior to drawing the 'fill' (both using the same StrokeStyle!):

' update m_transGeom based on m_widenedPathGeometry & the current transform matrix3x2,
m_transGeom = New TransformedGeometry(D2DCanvas.canvas_factory2D, m_widenedPathGeometry, Matrix3x2.Rotation(m_rotation, InsertPoint) * _transformMatrix)
'   to draw the stroke of the Polyline
D2DCanvas.canvas_renderTarget2D.DrawGeometry(m_transGeom, m_strokeBrush, plaatdikte * _transformMatrix.ScaleVector(1), m_strokeStyle)

' update m_fillTransformedGeometry based on m_pathGeometry & the current transform matrix3x2,
m_fillTransformedGeometry = New TransformedGeometry(D2DCanvas.canvas_factory2D, m_pathGeometry, Matrix3x2.Rotation(m_rotation, InsertPoint) * _transformMatrix)
' to draw the fill of the PolyLine
D2DCanvas.canvas_renderTarget2D.DrawGeometry(m_fillTransformedGeometry, m_fillBrush, plaatdikte * _transformMatrix.ScaleVector(1), m_strokeStyle)

This generates an undesired effect on the End-Caps: (Either rounded, wich isn't defined in the StrokeStyle or something in between)

This Stroke/Fill - method kindof works correctly when I redefine the used StrokeStyle to have 'rounded' endcaps:

But the 'flat' end-caps is really what I'm after.

Any ideas why this is happening, or how I could tackle this differently ?

Cheers !