Solved

# Caraf G

Posted on 2000-04-06
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For an extra 50 -

Further to our discussion on using CopyMemory to pass lists about:
I am getting an error with reading the memory.  Is there a maximum size of memory that I can copy?

I am now passing more points (as I need ordered triangles for OpenGL)

Dim mysglcoord() As sglCoordinate3D
Dim mycoords As Single
Dim i As Long

ReDim mysglcoord(1 To MyTSB.numTriangleCoords)

mycoords = MyTSB.sglTriangleCoords
CopyMemory VarPtr(mysglcoord(1)), mycoords, 12 * (MyTSB.numTriangleCoords)

Call glBegin(GL_TRIANGLES)
For i = 1 To MyTSB.numTriangleCoords
Call glColor3f(1#, 1#, 0#)
Call glVertex3f(mysglcoord(i).x, mysglcoord(i).y, mysglcoord(i).z)
Next i
Call glEnd
Call glFlush

I get the message:
The instruction at "0x77f970ab" referenced memory at "0x0ab7200". The memory could not be "read".

You know, the standard crashing error.  The size of the operation is all I can think of.
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Author Comment

The error occurs on the line CopyMemory
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Author Comment

OK I have realised that the Ptr is a long instead of a single.
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Expert Comment

Does that mean you solved the problem?

If not, can you post the type definition for MyTSB?
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Author Comment

No I haven't solved the problem.

MyTSB.sglTriangleCoords fills an array:

Type VertexCoord
x as single
y as single
z as single
end type

redim vertCoord(1 to numTriangleCoords) as vertexcoord

Then passes VarPtr(vertcoord(1)) back as a long.

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Author Comment

Public Function sglTriangleCoords() As Long
Dim pointCounter As Long
Dim i As Long
Dim j As Long
Dim sglCoords() As VertexCoordinate

pointCounter = 1

ReDim sglCoords(1 To numTriangleCoords)

For i = 1 To MyTSB.SurfacePolygonIndices.Npolygons
For j = 1 To MyTSB.SurfacePolygonIndices.SurfacePolygon(i).Nsides
sglCoords(pointCounter) = MyTSB.VertexCoords.VertexCoordinate(MyTSB.SurfacePolygonIndices.SurfacePolygon(i).IndicesShort(j) + 1)
pointCounter = pointCounter + 1
Next j
Next i

sglTriangleCoords = VarPtr(sglCoords(1))
'sglTriangleCoords = sglCoords(1)
End Function
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Expert Comment

Hmmmm. Should be OK. A Single is 4 bytes too.

Perhaps a completely different tack is needed here. You may have to do some class programming after all...
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Expert Comment

Ok, look at this idea:

1) Create a DLL with the following class (Class1)

Option Explicit
Private Type VertexCoordinate
a As Single
b As Single
c As Single
End Type
Private arrTheThreeSinglesArray() As VertexCoordinate
Public Sub FillIt(lngLBound As Long, lngUBound As Long)

Dim lngCounter As Long
ReDim arrTheThreeSinglesArray(lngLBound To lngUBound)
For lngCounter = lngLBound To lngUBound
arrTheThreeSinglesArray(lngCounter).a = lngCounter * 1
arrTheThreeSinglesArray(lngCounter).b = lngCounter * 2
arrTheThreeSinglesArray(lngCounter).c = lngCounter * 3
Next

End Sub
Public Property Get tLBound() As Long

tLBound = LBound(arrTheThreeSinglesArray)

End Property
Public Property Get tUBound() As Long

tUBound = UBound(arrTheThreeSinglesArray)

End Property
Public Property Get tA(Index As Long) As Single

tA = arrTheThreeSinglesArray(Index).a

End Property
Public Property Get tB(Index As Long) As Single

tB = arrTheThreeSinglesArray(Index).b

End Property
Public Property Get tC(Index As Long) As Single

tC = arrTheThreeSinglesArray(Index).c

End Property

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Accepted Solution

caraf_g earned 50 total points
Then, the calling program could use it as follows:

Option Explicit
Private Type VertexCoordinate
a As Single
b As Single
c As Single
End Type
Private Sub Command1_Click()

Dim objX As Class1
Dim typY As VertexCoordinate
Set objX = New Class1
objX.FillIt 1, 3

Dim lngCounter As Long

For lngCounter = 1 To 3
typY.a = objX.tA(lngCounter)
typY.b = objX.tB(lngCounter)
typY.c = objX.tC(lngCounter)
'Now you can use typY here
Next

End Sub
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Author Comment

won't this slow the performance somewhat?
I'll give it a go though!!
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Author Comment

The display flickers a bit when rotating the shape, but its good!!
Thanx again Caraf :)
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Expert Comment

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