transparent bitmaps
lazarus / 39-Graphics

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Jo · 2007-11-18 11:01

Is there a way to draw transparent bitmaps? The example for win32
using writing and reading from TMemoryStream gives on wince the
following: “Failed to get raw image description from bitmap”. Any
ideas how I can go about this?

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Marc · 2007-11-19 10:52

This should work, do you have a code example ?

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Jo · 2007-11-19 12:22

Just copied and adjusted the example. The error is when writing the
bitmap to the stream, and the bitmap is drawn correctly if I don't use
transparency and streams:

procedure TForm1.Button2Click(Sender: TObject);
var
  buffer: THandle;
  bmp: TBitmap;
  memstream: TMemoryStream;
begin
  bmp := TBitmap.Create;
  bmp.Width:=32;
  bmp.Height:=32;
  //bmp.PixelFormat:=pf24Bit ;
  Handle := LoadBitmap(hInstance, 'test');

  if (buffer = 0) then exit; // Error loading the bitmap

  bmp.Handle := buffer;
  memstream := TMemoryStream.create;
  try
    bmp.SaveToStream(memstream);
    memstream.position := 0;
    bmp.LoadFromStream(memstream);
  finally
    memstream.free;
  end;

  bmp.Transparent := True;
  bmp.TransparentColor := clblack;

  Canvas.Draw(100, 150, bmp);
 

  bmp.Free; // Release allocated resource


end;

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Marc · 2007-11-19 13:36

Changing pixelformat doesn't work yet. Only pfDevice is supported.

BTW, I hope this is a typo: Code: [Select]Handle :=
LoadBitmap(hInstance, 'test');
I would expectCode: [Select]buffer := LoadBitmap(hInstance, 'test');

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Jo · 2007-11-19 15:18

Quote
BTW, I hope this is a typo:

Yes, it was from testing bmp.Handle:=...
The code works fine on win32 compilation but the wince creates the
error when writting the bitmap to the stream at:
bmp.SaveToStream(memstream);

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Marc · 2007-11-19 15:52

ok, can you bugrep this, with sample code and sample image (otherwise
this might get forgotten)

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Jo · 2007-11-20 08:22

ok.