application window flashes on Windows 10 when built using Lazarus 1.6
lazarus / 34-Windows

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omarG · 2016-08-31 16:47

I have a Windows application that is using WinApi with no fpc\Lazarus
components.  My windows are created with a Composite window style.

When using Laz version 1.6 to compile makes my app flicker with every
mouse move, while compiling the same app using version 1.2 is working
without any flicker.  This is true in Windows 10 only!  In any other
Windows system, the app is working fine.  

Reading some forum entries, I tried to put the Windows first in the
Uses, but it did not help.

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omarG · 2016-09-05 13:44

Am I the only one to experience this problem or are most of you don't
use pure WinApi to create and talk to the windows?

How could the same code compiled in Lazarus 1.2 with fpc 2.6.2 work
perfectly while compiling in the latest version of fpc and Lazarus
cause so much flashing?

Please Help.

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rvk · 2016-09-05 13:50

Maybe providing a small test-project where you create your form (other
than the standard Lazarus-GUI way) could help.

Does a normal Lazarus-GUI app flicker for you too on Windows 10?

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omarG · 2016-09-09 17:07

Thanks for looking into this problem.

It turns out that on Windows 10 and fpc 3.0 creating a double buffer
window needs BOTH extended styles:

WS_EX_COMPOSITED and WS_EX_LAYERED. 

For some reason when WS_EX_LAYERED was omitted while compiling with
fpc 2.6.2 there was no flashing on Windows 10.

Remember WS_EX_LAYERED should be present on XP.