X, backingstore and opengl

Angelo Graziosi angelo.graziosi@alice.it
Mon Nov 24 14:58:00 GMT 2008

I want to flag the following problems I have met with X11R7.4 and the
application ROOT [1].

To reproduce them, you should not need to rebuild ROOT under X11R7.4
but it is sufficient to install pre-built binaries, even if they
result from a build under the previous X11R6.99: the 'effects' are the

To install pre-built binaries, you have to do the following:

wget ftp://root.cern.ch/root/root_v5.21.04.win32gcc-gcc-3.4.tar.gz
tar -xzf root_v5.21.04.win32gcc-gcc-3.4.tar.gz -C /usr/local/

cd /usr/local

export ROOTSYS=/usr/local/root
export PATH="${PATH}:/usr/local/root/bin"
export LD_LIBRARY_PATH="${LD_LIBRARY_PATH}:/usr/local/root/lib"

cd root/tutorials/

Now the problems.

I have always started the X server with the option '+bs', i.e.

    XWin -multiwindow -clipboard -silent-dup-error +bs

(for example with a startxwin-2.bat which differs from the default
only by '+bs')

It enables the 'backingstore' which enable the 're-display' when two X
windows are overlapped (otherwise they appear corrupted).

With X11R7.4 here is what happens:


$ root

root [0] .x hsimple.C

At ROOT prompt (root [0]), you have to type '.x hsimple.C', which means
"run (.x) the macro hsimple.C"; hsimple.C is a block of C/C++ code
which ROOT executes as an interpreter.

Well, after this, not only ROOT segfaults, but also the X server

If, instead, I DO NOT start X with +bs, i.e. if I use:

    XWin -multiwindow -clipboard -silent-dup-error

(for example with the default startxwin.bat), the above example and
others work fine, but...

Many ROOT tutorials/examples are OpenGL applications, for example
'geom/shapes.C'. In this case, only ROOT segfaults as follows:


$ root

root [0] .x ./geom/shapes.C
root [1] Error in <RootX11ErrorHandler>: BadMatch (invalid parameter
attributes) (XID: 14680185, XREQ: 62)
assertion "!c->xlib.lock" failed: file
line 73

Obviously, under X11R6.99 all the above works just fine.

cygcheck.out and XWin.0.log attached.


[1] http://root.cern.ch

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