I try to send TBitmap to DLL, edit it there and return back.

of course there's no error checking, also on DLL side you should validate incoming parameters

ziolko.

oops should be:

  finally
    ms.Free;
    bmp.Free;  
  end;

ziolko

damn I'm trying to post here faster than I think:)

procedure MakeColorAnalysis(Buffer: Pointer;var Size: Int64);stdcall;
var ms: TMemoryStream;
    bmp: TBitmap;
begin
  if Assigned(Buffer) and (Size > 0) then begin
    ms := TMemoryStream.Create;
    bmp := TBitmap.Create;
    try
      ms.Write(Buffer^, Size);
      ms.Position := 0;
      bmp.LoadFromStream(ms);
      bmp.Canvas.MoveTo(10, 10);
      bmp.Canvas.LineTo(100, 100);
      ms.Clear;
      bmp.SaveToStream(ms);
      Size := ms.Size;
      ms.Position := 0;
      ReallocMem(Buffer, Size);
      ms.Read(Buffer^, Size);
    finally
      ms.Free;
      bmp.Free;
    end;
  end;
end;


ziolko.

It works, thank u very much ziolko :-)

I made small change here:

procedure TForm1.Button4Click(Sender: TObject);
var ms: TMemoryStream;
    buff: Pointer;
    sze: Int64;
begin
  ms := TMemoryStream.Create;
  Image1.Picture.Bitmap.SaveToStream(ms);
  ms.Position := 0;
  sze := ms.Size;
  GetMem(buff, sze);
  ms.Read(buff^, sze);

  {ms.Clear;
  Image1.Picture.Bitmap.LoadFromStream(ms);
  Repaint;
  Image1.Repaint;}
  MakeColorAnalysis2(buff, sze);
  ms.Clear; //new
  ms.Write(buff^, sze);
  ms.Position := 0;
  Image1.Picture.Bitmap.LoadFromStream(ms);

  ms.Free;
end;

II do not understand how it works (additional question if I may :-) ):

Within DLL:

      ReallocMem(Buffer, Size);
      ms.Read(Buffer^, Size); //why do we need it? I thought that Buffer is a Pointer pointing to
                                              //the beginning of the memory used to store Stream so
                                              //I thought that Pointer stores address of kind of ONE memory cell
                                              //not the whole memory stream, so continuing this way of thinking I    
                                              //expected that we do not need to change this pointer at all,
                                              //thought that MemoryStream starts in the same place in memory and only
                                              //it's lenght may change- any comment on these thoughts? :-)


Thank u very much

panJames

see what happens on EXE side:
  GetMem(buff, sze);
  ms.Read(buff^, sze);
we alloc memmory "under" buff and COPY contents of stream into buff then buff is passed to DLL

>>I thought that Pointer stores address of kind of ONE memory cell not the whole memory stream

nope, buffer stores whole contents of stream.

in other words. From EXE perspective we dump stream to buffer then let the DLL do whatever it's supposed to do when DLL is done reload buffer to stream and display in image.
from DLL perspective we got pointer to some buffer so we load it to stream do our job when done dump it back to buffer.

ReallocMem is required as after drawing on bitmap's canvas size of picture may be different than orginal

ziolko.

we could pass only pointer to streams data like this:

MakeColorAnalysis2(ms.Memory, sze);

but memorystream has properties like Size and Position which we can't update from DLL.

ziolko.

Thank u very much for answers,
if possible please have a look at my next question:

'Passing a bitmap to DLL using handle to it'


Polon