This is not a problem you might say. Try it and you'll find that nothing appears to be drawn. If you do the same thing in B4A it works as expected.

The reason is that the JavaFx designers differentiated between lines and line shapes. The DrawLine method draws lines, the DrawPath method draws closed shapes.

In B4J if you draw a shape, the points in the path describe the outside edge of the shape. So the inside of a closed path of a line is empty, no matter how thick you make the stroke width.

The solution is to turn the line into a line shape by making it a thin rectangle. That is fairly easy if the line is horizontal or vertical, but if it is on an angle, it requires some trigonometry.

I knew that, but a recent question by @labcold https://www.b4x.com/android/forum/threads/b4x-canvas-path-differences-between-b4a-and-b4j.132810/

made me revisit the issue and wrote a sub ("listToPath") that adjusts the path of a shape if the path describes a line. Because the points in a loaded path are not available, the method works if you generate the points on the path as a List of points (2 element Arrays). The Sub converts the List into an path that makes an adjustment for lines.

Edit: I changed the name of the path in the subroutine, the earlier name was from a previous version which would cause confusion. The change is tested.

The reason is that the JavaFx designers differentiated between lines and line shapes. The DrawLine method draws lines, the DrawPath method draws closed shapes.

In B4J if you draw a shape, the points in the path describe the outside edge of the shape. So the inside of a closed path of a line is empty, no matter how thick you make the stroke width.

The solution is to turn the line into a line shape by making it a thin rectangle. That is fairly easy if the line is horizontal or vertical, but if it is on an angle, it requires some trigonometry.

I knew that, but a recent question by @labcold https://www.b4x.com/android/forum/threads/b4x-canvas-path-differences-between-b4a-and-b4j.132810/

made me revisit the issue and wrote a sub ("listToPath") that adjusts the path of a shape if the path describes a line. Because the points in a loaded path are not available, the method works if you generate the points on the path as a List of points (2 element Arrays). The Sub converts the List into an path that makes an adjustment for lines.

Edit: I changed the name of the path in the subroutine, the earlier name was from a previous version which would cause confusion. The change is tested.

B4X:

```
Sub AppStart (Form1 As Form, Args() As String)
MainForm = Form1
MainForm.RootPane.LoadLayout("Main")
MainForm.Show
cvs.Initialize(pnlGraph)
Dim fromCenter As List: fromCenter.Initialize
fromCenter.Add(Array(-0.4, 0.0))
fromCenter.Add(Array(-0.2, 0.0))
fromCenter.Add(Array(0.0, 0.0))
fromCenter.Add(Array(0.2, 0.0))
fromCenter.Add(Array(0.4, 0.0))
drawRotatedShape (fromCenter, 250, 250, 2, 200, 30)
End Sub
Private Sub drawRotatedShape(FromCenter As List, CenterX As Float, CenterY As Float, Thickness As Float, Radius As Float, Angle As Float)
Dim pntList As List: pntList.Initialize
For Each pt() As Object In FromCenter
pntList.Add(Array(CenterX + pt(0).As(Float) * Radius, CenterY + pt(1).As(Float) * Radius))
Next
cvs.DrawPathRotated(listToPath(pntList, Thickness), xui.Color_Black, True, Thickness, Angle, CenterX, CenterY)
End Sub
Private Sub listToPath(pntList As List, thickness As Float) As B4XPath
'This method works for all shapes - it determines whether the shape is a line shape and then adjusts the path
Dim aPath As B4XPath
Dim epsilon As Float = .001
Dim firstPt(2), lastPt(2), prevPt(2) As Object
Dim isHorizontalLine = True, isVerticalLine = True, isOtherLine = True As Boolean
For i = 0 To pntList.Size - 1
Dim pt() As Object = pntList.Get(i)
Select i
Case 0
firstPt(0) = pt(0)
firstPt(1) = pt(1)
Case pntList.Size - 1
lastPt(0) = pt(0)
lastPt(1) = pt(1)
End Select
If i = 0 Then
aPath.Initialize(pt(0), pt(1))
Else
aPath.LineTo(pt(0), pt(1))
If Abs(prevPt(0) - pt(0)) > epsilon Then isVerticalLine = False
If Abs(prevPt(1) - pt(1)) > epsilon Then isHorizontalLine = False
End If
prevPt(0) = pt(0)
prevPt(1) = pt(1)
Next
If isVerticalLine Then
aPath.LineTo(lastPt(0) + thickness, lastPt(1))
aPath.LineTo(firstPt(0) + thickness, firstPt(1))
Else If isHorizontalLine Then
aPath.LineTo(lastPt(0), lastPt(1) + thickness)
aPath.LineTo(firstPt(0), firstPt(1) + thickness)
Else
Dim deltaX As Float = lastPt(0) - firstPt(0)
Dim deltaY As Float = lastPt(1) - firstPt(1)
If Abs(deltaX) < epsilon Then
isOtherLine = False
Else If Abs(deltaY) < epsilon Then
isOtherLine = False
Else
Dim overallSlope As Float = deltaY / deltaX
Log(overallSlope)
prevPt(0) = firstPt(0)
prevPt(1) = firstPt(1)
For i = 1 To pntList.Size - 1
Dim pt() As Object = pntList.Get(i)
Dim thisSlope As Float = (pt(1) - prevPt(1)) / (pt(0) - prevPt(0))
If Abs(overallSlope - thisSlope) > epsilon Then
isOtherLine = False
Exit
End If
prevPt(0) = pt(0)
prevPt(1) = pt(1)
Next
End If
If isOtherLine Then
Dim offsetX, offsetY As Float
Dim angle As Float = cPI / 2 + ATan(overallSlope)
offsetX = thickness * Cos(angle)
offsetY = thickness * Sin(angle)
aPath.LineTo(lastPt(0) + offsetX, lastPt(1) + offsetY)
aPath.LineTo(firstPt(0) + offsetX, firstPt(1) + offsetY)
End If
End If
Return aPath
End Sub
```

Last edited: