[Lazarus] Scanline on certain size images seems to be failing : Access Violation...

[Mattias Gaertner]

On Sat, 15 Aug 2009 09:26:59 -0400
<dominique at savagesoftwaresolutions.com> wrote:

> Please ignore,
>   I just realised that ScanLineImage.Free was being called before the
> Color_RGBtoColor funcation. Which caused the AV.
> Hence why the code works under Delphi, but was AVing with FreePascal.

Note:
The ScanLine differences have nothing to do with FPC, but with the LCL.
You can use:

{$IFDEF LCL}

Mattias


> 
> Dominique.
> 
> On Sat, 15 Aug 2009 08:28:53 -0400,
> <dominique at savagesoftwaresolutions.com> wrote:
> > I have the following 2 functions to determine the transparency
> > colour of
> a
> > bitmap...
> > 
> > // Returns the transparent color for the bitmap
> > function Bitmap24_TransparentColor(bitmap:TBitmap):TColor;
> > var
> >   row : PRGBArray;
> >   {$IFDEF FPC}
> >   ScanLineImage : TLazIntfImage;
> >   {$ENDIF}
> > begin
> >   Result := clBlack;
> > 
> >   if not IsValidBitmap( bitmap, 'Bitmap24_TransparentColor' ) then
> >   begin
> >     Exit;
> >   end;
> > 
> >   {$IFDEF FPC}
> >   ScanLineImage := bitmap.CreateIntfImage;
> >   {$ENDIF}
> > 
> >   {$IFDEF FPC}
> >   row := ScanLineImage.GetDataLineStart( bitmap.Height - 1 );
> >   {$ELSE}
> >   row := bitmap.ScanLine[ bitmap.Height - 1 ];
> >   {$ENDIF}
> > 
> >   {$IFDEF FPC}
> >   ScanLineImage.Free;
> >   {$ENDIF}
> > 
> >   Result := Color_RGBtoColor(row[0]); 
> > end;
> > 
> > // Transforms a RGB color into a standard color
> > function Color_RGBToColor(col : TRGB) : TColor;
> > begin
> >   Result := $10000 *  col.b + $100 * col.g + col.r; // ACCESS
> > VIOLATION HERE if Image greater than 640x480
> > end;
> > 
> > I'm getting an Access violation when passing the row[0] to the
> RGBtoColor.
> > Can anyone see what I might be doing wrong?
> > The only thing I noticed is that it seems to fail when I use images
> greater
> > than 640x480, but I'm willing to concede it may be a bit depth
> > issue. Smaller image sizes seem to work fine.
> > 
> > Would I be right in thinking that row[0] is the bottom right corner
> > of
> the
> > image?
> > 
> > Thanks,
> > 
> > Dominique.
> > 
> > --
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> 
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