[GRASS5] Fw: [winGRASS] XGetImage/XPutImage in libG11.

Mike Thomas mthomas at gil.com.au
Thu Dec 6 08:25:43 EST 2001

Hi there.

Reposting for wider input with further comments based on more testing.

Below is a list of problems I had with the Win32 version of "i.points",
using the native XDriver rather than X11.

Has anyone noted similar problems with "i.points" under Unix?


Mike Thomas

----- Original Message -----
From: "Mike Thomas" <miketh at brisbane.paradigmgeo.com>
To: <wingrass at grass.itc.it>
Sent: Thursday, December 06, 2001 3:39 PM
Subject: [winGRASS] XGetImage/XPutImage in libG11.

> Hi all.
> I have just checked into CVS some new work on the XPut/GetImage() problem
> for libG11, which is designed to support the Panel save and restore code
> used extensively in, for example,  "i.points".
> Panel save and restore don't work yet, although the program no longer
> crashes as it did when XGetImage() returned NULL.
> Outstanding bugs can be seen by running "i.points" and
> 1. Watching the twin horizontal lines across the center of the monitor,
> which on my computer at least, end up displaced upwards by a small amount
> after the panel is replaced.

One pixel to be precise.

> 2. Using the zoom/point menu, which seems to cause random images to appear
> when the panel is restored - sometimes black, sometimes fragments of the
> image.
> 3. Looking at the code for XPutImage() in "xlib.c", the call to
> SetDIBitsToDevice{} needs the source "y" value set to the top left rather
> than the bottom left corner of the incoming image in order to get some
> semblance of the saved panel to reappear - otherwise, if set to "sy +
> height -1" as it used to be, rather than "sy" as currently checked in, you
> get a white background (possibly a refresh problem?).

Actually, the white background is just the leftovers of the menu - ignore
this theory about refresh.

> 4. Resizing the XDriver during "i.points" hangs both the display and the
> Grass shell.  Is this true on Unix too?
> I believe that I am missing something about which location the images
> be written to (point 3 above), and their orientation (bottom left vs top
> left).
> I have checked that one image obtained by XGetImage() and passed through
> panel save and restore, finally arriving at XPutImage() is preserved
> those steps exactly - so the display writing phase with
> is definitely going wrong.  It may be, of course, that other images are
> preserved.

Furthwe testing shows that other images are also preserved from capture to
the point before redisplay.

> Cheers
> Mike Thomas
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> winGRASS at grass.itc.it
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