Hello,

I've recently purchased a Wacom Intuos graphics tablet.  I am very pleased
with GIMP's support for the tablet, and I've had a great time working with
it.

However, there's one obscure feature that still troubles me.  I'm trying
to make Image Pipes where the ranks are chosen according to the X-tilt and
the Y-tilt of the Intuos stylus.  The results I've gotten are pretty
strange.  I've written up a short document trying to describe what's
happening, and I'm attaching it with this letter.

Here are the explanations I see for what's been happening:

1. The driver I have for the Intuos is sending bad information.  This is
entirely possible.  I downloaded a driver binary off the web.  The site
where I found it had no description of what the driver was or who wrote
it.

2. GIMP support for X and Y tilt is a little buggy.  I'd find this
understandable.  Image Pipes are a somewhat obscure feature, and X and Y
tilt are an obscure feature of an obscure feature.  

So, I'd like to know whether X and Y tilt have been proven to work on
other systems, and, if so, with what version of X and which drivers.

I'm already very grateful to anyone who has worked on GIMP, and my thanks
in advance to anyone who can help me with this issue.

Tilt Behavior Description

This is a brief behavior of how the Xtilt and Ytilt behavior of the
GIMP image pipes function.  The machine I found this behavior on is a
Redhat 7.0 machine with a 2.4 kernel and an Intuos USB Graphics tablet.
The behavior of Xtilt and Ytilt is very similar, so I will describe Xtilt
in this document, and the reader can imagine Ytilt as the same thing,
only 90 degrees clockwise.

When I refer to the tilt, I am referring to the angle of the stylus to
the surface of the tablet.  0 degrees describes the tilt when the stylus
is lying on the surface of the tablet pointing due east.  90 degrees
is the tilt of the stylus when it is pointing directly at the tablet.
180 degrees is the tilt of the stylus when it is lying on the tablet
pointing due west.

When I refer to brushes, I'm referring to the individual segments of the
image pipe.  When an image pipe is saved to select brushes based on Xtilt,
one of these segments will be chosen depending on the tilt of the pen.
The first brush is the topmost layer when the image pipe is saved.
The last brush is the bottom layer.

The behavior I expect is that the tilt would be divided up between
the possible brushes, with each brush taking an equal portion of the
possible angles.  For instance, if there were four brushes, the first
brush would be chosen for a tilt of 0-45 degrees, the second brush for
a tilt of 45-90 degrees, the third brush for a tilt of 90-135 degrees
and the last brush for a tilt of 135-180 degrees.

But the behavior I'm getting is this: If an image pipe has only two
brushes, I find that the last brush is always chosen, no matter what
the tilt is.  If there are four brushes, the last brush is chosen when
the tilt of the stylus is between roughly 60 and 180 degrees.

I have tried using up to 25 brushes, and it appears the last brush always
gets chosen for at least 90 degrees of tilt (half the possible angles).
With 25 brushes, it seems that the 85-180 degrees of tilt result in
choosing the last brush.  It also appears that the first half or so of
the brushes is never chosen.

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