Hello,

I working with alpha blending. On QT it works fine. On GTK2 I get "Depth: 24" when executing "GetDescriptionFromDevice(0)" (on QT -> 32). Why GTK2 "screen" not supports alpha?
It is strange because if I load PNG with transparency (image with gradient) into TImage then I clearly can see alpha blending effect on GTK2 when image is diplayed. Maybe I must to use
"GetDescriptionFromDevice" not from screen? From where then?

There is full "DataDescription" on GTK2:
Format: ricfRGBA
Width: 3
Height: 3
Depth: 24
BitOrder: riboBitsInOrder
ByteOrder: riboLSBFirst
LineOrder: riloTopToBottom
LineEnd: rileDWordBoundary
BitsPerPixel: 32
RedPrec: 8
RedShift: 16
GreenPrec: 8
GreenShift: 8
BluePrec: 8
BlueShift: 0
AlphaPrec: 0
AlphaShift: 0
MaskBitsPerPixel: 1
PaletteColorCount: 0

System Kubuntu 16.10; lazarus 1.9.0; fpc 3.0.0.

P.S. sorry for my bad English.

Iirc (its long ago when i implemented it) the alphablending is done by the underlying rawimage implementation

Marc

2017.04.14 22:02, Marc Weustink via Lazarus rašė:

I tried to put 32 bit image in to TImage (on GTK2) and alphablending works. Is this means that I can always put an image with 32 bit depth in to TImage when "GetDescriptionFromDevice(0)" says "screen" supports "Depth: 24"? If not always then how to know when I can?

Lazarus uses GDK instead of Cairo for most graphics stuff in GTK2 and GDK simply wraps X11 which doesn't support alpha blending. AFAIK GTK2 was using only GDK for graphics but at some point they switched to Cairo which does all graphics operations in the CPU and allows for alpha blending in X11. However Lazarus didn't switch (i suppose for binary compatibility with GTK2 versions that didn't have Cairo).

As a result practically all images from Lazarus to GTK2 had their alpha channel dropped, including toolbar icons, messages, etc. I submitted a patch for this a few years ago that handles the most common action - drawing a bitmap to a widget or another bitmap. This is a special case and doesn't fix the issue entirely, but at least allows toolbars, buttons, timages, etc to do alpha blending.

A proper full fix would be to rewrite all GTK2 graphics code to use Cairo instead of GDK, but that would take a lot of time, can break existing applications due to unforeseen bugs and with GTK2 being obsoleted in favor of GTK3 i am not sure if it is worth the effort.

For further details you can check bug 25491 here:

http://mantis.freepascal.org/view.php?id=25491

On Fri, Apr 14, 2017 at 10:23 PM, Valdas Jankūnas via Lazarus <

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On Sun, 16 Apr 2017 02:53:00 +0300

Kostas Michalopoulos wrote

[...] A proper full fix would be to rewrite all GTK2 graphics code to use Cairo instead of GDK, but that would take a lot of time, can break existing applications

You can do it with IFDEFs.

due to unforeseen bugs and with GTK2 being obsoleted in favor of GTK3 i am not sure if it is worth the effort.

A strong point. IMO you should better spend your time on improving the LCL Gtk3 interface.

Mattias

Still has Graphics32 and AGG library?

On Mon, Apr 17, 2017 at 7:53 PM, Mattias Gaertner via Lazarus <

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And, I think Lazarus more make / stable on win32 than linux, what you do on linux majorly doing command program / services

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