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Converting Delphi Win32 code to Delphi.NET with pointer arithmetic

Posted on 2008-10-14
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Last Modified: 2013-11-23
I am trying to convert some Delphi Win32 code to Delphi.NET (in Delphi 2007). I am getting an error "E2089 Invalid typecast".

The function is taking a dib handle as a parameter and attempting to return a pointer to the image data bits. How do I do this properly in Delphi.NET?
{$UNSAFECODE ON}
function TEsImage.GetPtrToBits: Pointer; {$IFDEF CLR}unsafe;{$ENDIF}
var
  imageBits: Pointer;
  bitmapInfo: PBitmapInfo;
  numberOfColors: Integer;
begin
  bitmapInfo := PBitmapInfo(GlobalLock(FDIB));
  if Assigned(bitmapInfo) then begin
    { Get number of colors }
    if bitmapInfo.bmiHeader.biClrUsed > 0 then begin
      numberOfColors := bitmapInfo.bmiHeader.biClrUsed
    end else begin
      if (bitmapInfo.bmiHeader.biBitCount <> 24) and (bitmapInfo.bmiHeader.biBitCount <> 16) then begin
        numberOfColors := 1 shl bitmapInfo.bmiHeader.biBitCount;
      end else begin
        numberOfColors := 0;
      end;
    end;
 
    // THIS IS THE LINE GIVING THE TYPECAST COMPILER ERROR
    imageBits := Pointer(DWORD(bitmapInfo) +
                  SizeOf(BITMAPINFOHEADER) +
                  bitmapInfo*SizeOf(RGBQUAD));
 
    result := pointer(imageBits);
  end else begin
    result := Nil;
  end;
  GlobalUnLock(FDIB);
end;
{$UNSAFECODE OFF}

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Question by:llanphear
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5 Comments
 
LVL 6

Expert Comment

by:ChristianWimmer
ID: 22713647
I think you must convert bitmapInfo first as you did the first time.
imageBits := Pointer(DWORD(bitmapInfo) +
                  SizeOf(BITMAPINFOHEADER) +
                  DWORD(bitmapInfo)*SizeOf(RGBQUAD));

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Author Comment

by:llanphear
ID: 22713793
Whoops I had an error in the line. Still does't work though
imageBits := Pointer(DWORD(bitmapInfo) +
                  SizeOf(BITMAPINFOHEADER) +
                  numberOfColors*SizeOf(RGBQUAD));

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LVL 27

Accepted Solution

by:
BigRat earned 500 total points
ID: 22721876
I don't understand this, because it looks as if the code has been marked unsafe!!!

Why not try incrementing the pointer?

   Inc(bitMapInfo,a+b*c);
0
 

Author Closing Comment

by:llanphear
ID: 31505993
Thank you. My biggest mistake was expecting a return result from Inc().
0
 

Author Comment

by:llanphear
ID: 22725849
Here is the final bit of code in case anyone was interested...
var
  pInfo: PByte;
  imageBits: PByte;
  bitmapInfo: PBitmapInfo;
  numberOfColors: Integer;
begin
  pInfo := PByte(GlobalLock(FDIB));
  bitmapInfo := PBitmapInfo(pInfo);
  if Assigned(pInfo) then begin
    if bitmapInfo.bmiHeader.biClrUsed > 0 then begin
      numberOfColors := bitmapInfo.bmiHeader.biClrUsed
    end else begin
      if (bitmapInfo.bmiHeader.biBitCount <> 24) and (bitmapInfo.bmiHeader.biBitCount <> 16) then begin
        numberOfColors := 1 shl bitmapInfo.bmiHeader.biBitCount;
      end else begin
        numberOfColors := 0;
      end;
    end;
    Inc(pInfo, SizeOf(BITMAPINFOHEADER) + numberOfColors * SizeOf(RGBQUAD));
    imageBits := pInfo;
 
    FData := Pointer(imageBits);
 
  end else begin
    FData := Nil;
  end; 
  GlobalUnLock(FDIB);
end;

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