TImage problems
lazarus / 39-Graphics

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radioman · 2011-09-14 19:20

I'm trying to port a Delphi application to Lazarus (using Lazarus
0.9.30 and FPC 2.4.2) and I'm having problems with TImage.

The program uses a TImage to display a map, and over this image,
another TImage with transparent property enabled. On this second
TImage the program draw some locations and tracks.

The first problem is the transparent function does not work at all.
The second image starts transparent but as soon as I draw something on
it, it becomes not transparent (of course the lower left pixel is
untouched).

So I tried a slower workaround: I made the TImage with the map not
visible and everytime I need to mark something on the map, I copy the
canvas from the first image to the second one, and then I draw on the
second image.

The problem now is the TImage.Canvas.CopyRect procedure does not copy
the content of image. It copy the content of the area where the image
is. So instead a map, I get a perfect copy of buttons, comboboxes,
etc... exactly the portion of the form where the image is placed (but
not visible).

Am I missing something? Any ideas?

Thanks in advance!

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lainz · 2011-09-14 21:03

Quote from: radioman on September 14, 2011, 09:20:53 pmThe first
problem is the transparent function does not work at all. The second
image starts transparent but as soon as I draw something on it, it
becomes not transparent (of course the lower left pixel is untouched).
You must use color transparency because alpha is not available by
default.

Quote from: radioman on September 14, 2011, 09:20:53 pmThe problem now
is the TImage.Canvas.CopyRect procedure does not copy the content of
image. It copy the content of the area where the image is. So instead
a map, I get a perfect copy of buttons, comboboxes, etc... exactly the
portion of the form where the image is placed (but not visible).
Use Image.Picture (Image.Picture.Bitmap.Canvas) instead Image.Canvas.

Edit: here is the best explanation
http://wiki.lazarus.freepascal.org/Developing_with_Graphics#Draw_to_a_
TImage

If you want you can try BGRABitmap: it has alpha support - and
BGRAControls: for example you can use BGRAVirtualScreen to draw the
things you want in replace of TPaintBox, or TBGRASpriteAnimation in
replace of TImage..

BGRABitmap:
http://lazarus.freepascal.org/index.php/board,46.0.html
BGRAControls:
http://lazarus.freepascal.org/index.php/topic,12411.0.html

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radioman · 2011-09-14 23:46

Thank you for your response.

Setting TransparentColor does not do anything. The same weird
behaviour.

Using Image.Picture.Bitmap.Canvas instead Image.Canvas works, but it
is awful slow...

Thank you!

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Blaazen · 2011-09-15 00:10

You are using that "one color transparency", right?

Canvas.CopyRect does not work with it, only Canvas.Draw can work with
this kind of transparency.
On the page linked by lainz is described the trick with memstream to
activate transparency.

Code: [Select]memstream := TMemoryStream.create;
  try
    bmp.SaveToStream(memstream);
    memstream.position := 0;
    bmp.LoadFromStream(memstream);
  finally
    memstream.free;
  end;
So maybe you can use only one TImage and two TBitmaps (one for map and
the second for locations) and draw both these TBitmaps to TImage by
Canvas.Draw

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radioman · 2011-09-15 15:53

Thank you for the idea!