Hi, I was testing a sample project and found that on Windows, handling of PNGs with transparent backgrounds is working ok, but on Linux it doesn't work as expected. The image is a black line on the top of the image, with a Gaussian Blur applied on Photoshop, then saved to PNG with transparent background.

I attached an image showing what I get on Windows vs Linux, also the original image.

Thanks in advance,

No test source code?

Felipe Monteiro de Carvalho wrote

No test source code? -- Felipe Monteiro de Carvalho

Just place a TImage on a form, then load the attached png (sombra_bottom_horiz.png) into it.

Here it is anyway.

2011/4/10 Leonardo M. Ram? :

This error appears to me too: :(

[TImage] http://imagebin.org/147499
[TrayIcon] http://imagebin.org/147500 (normal transparency only in Windows >:(~ ).

Test in attached.

Lazarus 0.9.31 r30018M FPC 2.5.1 i386-linux-gtk 2

Afaik there is already a report for this in mantis.

The current linux-gtk implementation has only a 1 bit alpha

Marc

This is known issue. GTK have no alpha yet but I created set of components which partially solve this problem by using BGRABitmap class, details: http://www.lazarus.freepascal.org/index.php/topic,12411.0.html . Although there is no TImage yet but I can try create it.
For TrayIcon on GTK you must rebuild lazarus with -dUseStatusIcon switch. If tray still have no alpha then you must add this 3 lines posted by TrUsTeR: http://www.lazarus.freepascal.org/index.php/topic,6583.0.html After this tray icon works perfect in my case.

2011/4/10 Leonardo M. Ram?

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Well, I don't really need TImage, but TPicture. What I need is to be able to use TCanvas methods to copy this picture into another TCanvas.

Does your component allows this?

So if you want operate on bitmaps and canvas then maybe it is better to read about BGRABitmap and do this same things which i'm doing in my components. This is very interesting class. You can load PNG image to this class and draw wherever you want similar like with canvas (but with alpha). Details: http://wiki.lazarus.freepascal.org/BGRABitmap
and few tutorials (with nice effects):
http://wiki.lazarus.freepascal.org/BGRABitmap_tutorial This is crossplatform library

2011/4/12 Leonardo M. Ram?

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You are right Krzysztof, in fact, I adapted my code to BGRABitmap and it worked like a charm.

Just a note. I miss the LoadFromLazResource method, like TPicture. Do you plan to add this feature?.

I am not the author of BGRABitmap class but I think it is easy to assign bitmap from resource to BGRABitmap class. You can load image from resource using TResourceStream (there is tutorial on wiki) and then call BGRABitmap.LoadFromStream(MyResourceStream)

2011/4/12 Leonardo M. Ram?

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Krzysztof wrote

I am not the author of BGRABitmap class but I think it is easy to assign bitmap from resource to BGRABitmap class. You can load image from resource using TResourceStream (there is tutorial on wiki) and then call BGRABitmap.LoadFromStream(MyResourceStream)

I tried this and got an 'ExceptionException Unknown/Unsupported PCX image type'. The resource contains a PNG image.

  lRes := TLazarusResourceStream.Create('sombra_top_horiz', 'PNG');
  try
    lRes.Position:= 0;
    FMyTBGRABitmap.LoadFromStream(lRes);
  finally
    lRes.Free;
  end;

Any workaround?

I found a solution. To load the stream with a TFPReader, here's the code, for the record:

var
  lResTop: TLazarusResourceStream;
  lPngReader: TFPReaderPNG;
begin
  inherited Create(TheOwner);
  FShadowTop := TBGRABitmap.Create;
  FShadowBottom := TBGRABitmap.Create;
  lPngReader := TFPReaderPNG.create;
  lResTop := TLazarusResourceStream.Create('sombra_top_horiz', 'PNG');
  try
    lResTop.Position:= 0;
    FShadowTop.LoadFromStream(lResTop, lPngReader);
  finally
    lResTop.Free;
    lPngReader.Free;
  end;