Re: Internal-wm/rootless observations

Torrey Lyons Wed, 01 Dec 2004 08:53:14 -0800

I have been away on a long Thanksgiving vacation so I've been slow to respond. In any case, the 16 bpp modes are problematic but I believe we solved issues with them in the rootless code awhile back. The fundamental problem is that fb assumes screens are always 32-bit aligned. Thus you if a window's pixmap is not 32-bit aligned, fb assumes it can still access the word before the start of a drawable's data. In rootless mode, where windows are located higgledy-piggledy in memory, this is not true.

Rootless solves (or attempts to solve) this problem with the SetPixmapBaseToScreen() macro in rootlessCommon.h. The idea is that the unaligned window's pixmap is moved backwards in memory to align it and then a positive offset it given to fb to indicate where the window resides in the pixmap.

If there is an edge case where rootless does not work in 16-bits it would be good to track down. This mode is sometimes used on Mac OS X.

Hopefully that is helpful. I've got a review today but I can look at this in more detail tomorrow.

--Torrey

At 4:45 PM +0100 11/30/04, Alexander Gottwald wrote:

Hi all,

After many days of debugging the internalwm code i finally found
the actual problem.

The rootless code wants the pixmap buffer aligned to 32bit boundaries.
If the window width is odd and the xserver is run in 16bpp mode then
this is no guaranteed and this leads the strange errors.

Internalwm is only usable in 32bit mode.

This is not an actual problem. The goal should be anyway to work
with 32 bit visuals only and have real transparancy. I'm still
searching for a clean method to blit 32 bit bitmaps to 16 bit ones.
The simple aproach of allocating the bitmap with

CreateCompatibleBitmap()
bitmap->width = width
bitmap->height = height
bitmap->bpp = dbBPP
CreateDIBSection()

BitBlt(windowdc, ..., shadowdc, ...)

was not working properly. Is CreateCompatibleBitmap reusing the
DC from the screen? How can I create a 32bit bitmap if the desktop
is running in 16bit?

Anyway. Setting the bitmap depth to 32bit fixed the crashes I had
the last weeks with rootless but garbled the output. So the goal is
to have everything inside the server running at 32bit and let GDI do
the colorspace translation from 32 to 16 or 24 bit.

@zakki: I've found this in the code

  if (winIsInternalWMRunning(pScreenInfo))
    winAdjustXWindow (pWin, hwnd);

  winMWExtWMMoveResizeXWindow (pWin,

shouldn't that be

  if (winIsInternalWMRunning(pScreenInfo))
    winAdjustXWindow (pWin, hwnd);
  else
    winMWExtWMMoveResizeXWindow (pWin,

bye
        ago
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Re: Internal-wm/rootless observations

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