CGContextSetLineDash

Targets macOS
24

Ok… I have found the actual issue, and I think in the long run it is a bug in Xojo itself…

Turns out it only fails under a specific condition (which took a while to narrow down)

  • the app must be using Retina/HDPI and be on a Retina screen
  • the app must modifiy g.scaleX/Y … I did this in order to get a 1px wide line on a Retina screen. You will notice in the code I posted that I would multiple by the “current scale” … So I was storing the old scale, setting g.scalex=1 , drawing the line and restoring it to original. I remove that it works

SO HERE IS A VERSION THAT DOES WORK… I had to move the Scale math INSIDE the declares

#If TargetCocoa Then
  Declare Sub CGContextSetLineDash Lib "Cocoa" ( context As Integer, phase As CGFloat, lengths As Ptr, count As UInt32)
  Dim context As Integer = g.handle( g.HandleTypeCGContextRef )
  
  #If Target32Bit
    Const sizeOfSingle = 4
  #Else
    Const sizeOfSingle = 8
  #EndIf
  '
  g.AntiAlias=False
  lengths=Array(dash,spc) 
  //
  lengthArray=New MemoryBlock(sizeOfSingle*(1 + UBound(lengths)))
  For i = 0 To UBound(lengths)
    #If Target32Bit
      lengthArray.SingleValue(offset) = lengths(i)
    #Else
      lengthArray.DoubleValue(offset) = lengths(i)
    #EndIf
    offset = offset + sizeOfSingle
  Next
  //
  CGContextSetLineDash context,0,lengthArray,lengths.Ubound+1
  
  Dim oldScale As Double =g.scalex
  g.scaleX=1 // THIS MUST HAPPEN AFTER THE FIRST DECLARE CALL
  g.scaley=1
  x1=x1*oldscale
  y1=y1*oldscale
  x2=x2*oldscale
  y2=y2*oldscale
  //
  g.drawline x1,y1,x2,y2
  //
  g.scalex=oldScale 
  g.scaley=oldScale
  // return graphic context to original state
  CGContextSetLineDash context,0,Nil,0 ' solid line
  g.AntiAlias=aa_flag
#EndIf