Convert POINTAPI type

[Nanni]

Hi to all

I have an array of POINTAPI :

Private Type POINTAPI
        X As Long
        y As Long
End Type

and an Array of POINTSNG :

PrivateType POINTSNG
    X As Single
    y As Single
End Type

How can I convert the array of POINTSNG in a POINTAPI array without using a loop?

Thanks for suggestions

Nanni

[LaVolpe]

Though a single and a long both use 4 bytes, one might think CopyMemory can do the job. But don't try it. Example: if PointSNG.X was 3 and one used CopyMemory to move it to PointAPI.X, the result would be 1077936128 not 3.

Edited: If trying to move Long to Single, then same issue, different results: If PointAPI.X was 3 and moved to PointSNG.X with CopyMemory, value would be 4.203895E-45 not 3.

You will have to loop thru the array.

Edited Again. Is this for GDI+? Many GDI+ APIs have functions for arrays of singles and also arrays of long; matter of picking the right API.

[Nanni]

Hi LaVolpe

I need yo use Polygon and CreatePolygonRgn Gdi Api.

[LaVolpe]

Hi LaVolpe

I need yo use Polygon and CreatePolygonRgn Gdi Api.

Ok, simple question then: Why can't you just use POINTAPI only?

[Nanni]

Hi LaVolpe

I'm doing geometric transformations (using transformation matrix)
and all formulas use single values

[LaVolpe]

Hi LaVolpe

I'm doing geometric transformations (using transformation matrix)
and all formulas use single values

Ugh, got thinking cap on but don't immediately see any way to convert single to long without looping. Cannot simply move bytes between arrays for reasons in my first post. Exception: use GDI+ vs GDI but not exactly effortless.

[RhinoBull]

Though a single and a long both use 4 bytes, one might think CopyMemory can do the job. But don't try it. Example: if PointSNG.X was 3 and one used CopyMemory to move it to PointAPI.X, the result would be 1077936128 not 3...

The same will happen without api by simply assigning one array to another arrayLong = arraySng (you may need to redim destination ar first).

[Merri]

Well... this code does the trick of instantly moving the array from POINTSNG array variable to a POINTAPI array variable. No looping involved at all, but API declarations required. Advantage is that this is much faster than the CopyMemory solution and uses less memory, because there is only one array data segment at all times.

Option Explicit

Private Declare Function ArrPtr Lib "msvbvm60" Alias "VarPtr" (Arr() As Any) As Long
Private Declare Sub PutMem4 Lib "msvbvm60" (ByVal Ptr As Long, ByVal Value As Long)

Private Type POINTAPI
    X As Long
    Y As Long
End Type

Private Type POINTSNG
    X As Single
    Y As Single
End Type

Private Sub Form_Load()
    Dim PTSNG() As POINTSNG, PTAPI() As POINTAPI
    
    ' initialize PTSNG
    ReDim PTSNG(0 To 4)
    
    ' sample data
    PTSNG(0).X = 1
    PTSNG(0).Y = 0.1
    PTSNG(1).X = 2
    PTSNG(1).Y = 0.2
    PTSNG(2).X = 3
    PTSNG(2).Y = 0.3
    PTSNG(3).X = 4
    PTSNG(3).Y = 0.4
    PTSNG(4).X = 5
    PTSNG(4).Y = 0.5

    ' make PTAPI use the header of PTSNG
    PutMem4 ArrPtr(PTAPI), Not Not PTSNG
    ' "Not arrayvariable" will later cause an error in the IDE unless this is done
    Debug.Assert App.hInstance
    ' also make PTSNG use no header at all
    PutMem4 ArrPtr(PTSNG), 0
    
    ' sample output
    Debug.Print Hex$(PTAPI(0).X), Hex$(PTAPI(0).Y)
    Debug.Print Hex$(PTAPI(1).X), Hex$(PTAPI(1).Y)
    Debug.Print Hex$(PTAPI(2).X), Hex$(PTAPI(2).Y)
    Debug.Print Hex$(PTAPI(3).X), Hex$(PTAPI(3).Y)
    Debug.Print Hex$(PTAPI(4).X), Hex$(PTAPI(4).Y)
End Sub

However the sample output shows the problem LaVolpe and RhinoBull discuss with CopyMemory: the bits remain as they are and a Single value 1 is very much a different value when handled bitwise as Long.

Output of the above code

3F800000      3DCCCCCD
40000000      3E4CCCCD
40400000      3E99999A
40800000      3ECCCCCD
40A00000      3F000000