Debugging tablet issues on Windows

Andrew Chadwick edited this page Feb 16, 2017 · 8 revisions

:scream: Tablet glitches are harder to deal with on Windows. Here's how to help get them fixed.
:busts_in_silhouette: This page is part of our series describing how you can help MyPaint grow.
:hammer_and_wrench: Technical level: intermediate.

We get a lot of reported tablet issues on Windows which are a result of us using a separate library called GDK to handle tablet input. The "win32" backend to GDK is not very thoroughly tested for all possible tablets, because Windows is a minority operating system for the parent GTK+ project. Tablet support can be particularly hard to get working because the GTK developers don't have access to all tablet models out there.

When it works, it works. You may have to trust me on that. When it doesn't work, you may see:

  • Loss of precision: i.e. offsets between the cursor and the paint position. May be caused by multiple monitors.
  • Crashes: These are upstream issues which need to be reported to GTK's bug tracker. See Debugging crashes on Windows for a quick intro to capturing the info the developers will need.
  • Missing pressure or tilt. This may be caused by an incomplete tablet setup, or by a missing wintab32.dll.

We'll try to get you testing so that you can report the problem appropriately. But don't be discouraged if we ask you to report the problem elsewhere if it proves to be not our fault.

Testing with gtk3-demo from MyPaint

With the latest version, MyPaint comes with a tool called gtk3-demo. You can use this tool to help you decide whether the problem is within MyPaint or within GDK.

For example, if you do not get pen pressure in MyPaint, please test in gtk3-demo as well.

  • If that also does not have pen pressure, then your bug is not in MyPaint. It needs to be reported upstream, to the GTK+ developers.
  • If GTK3-Demo shows pressure, but MyPaint doesn't, then this is a MyPaint issue: no need to bug the upstream developers about it.

To open up the gtk3-demo, go to Start > MyPaint > "Test MyPaint-w64's tablet support (GTK3-Demo)". It will be called "Test MyPaint-w32's Tablet Support (GTK3-Demo)" instead, for w32 installs.

Testing with latest gtk3-demo from MSYS2

Sometimes tablet problem are already fixed on GDK but aren't present in any MyPaint bundles. To test against the latest GDK library, you will have to use MSYS2's gtk3-demo program. These instructions assume you are using a 64-bit Windows PC, windows 7 or later:

  1. Install msys2-x86_64-20161025.exe or later from in the time-honoured Windows way.

  2. In an MSYS2 shell, at the $ prompt, type:

pacman -Syyuu ⏎

Then follow the instructions in the output to update MSYS2. The ⏎ means to press the Return or Enter key - the one used to end paragraphs. It may have a symbol like ⏎ instead.

MSYS2 is a rolling software distribution, so you need to catch up before moving on to the next bit.

  1. Next, launch another MSYS2 shell, and type:
mkdir -p /mingw{32,64} ⏎
pacman -S msys2-launcher-git ⏎
pacman -S mingw-w64-x86_64-gtk3 ⏎

This installs the demo program we'd like you to use.

  1. Start a "native" MINGW64 shell using mingw64.exe or one of the shortcuts. In it, type:
gtk3-demo --gdk-debug=input --run=event_axes ⏎

This is a graphical test, and you can make the tablet test window bigger.


However the terminal output that gets shown as a result of the --gdk-debug=input parameter is very relevant for bug reporting as well. Please help us by pasting it into your bug report.

Reporting bugs in GTK or GDK

Bugs in these upstream libraries are handled via the GNOME project's bugzilla:

  • Search for your bug first. Likely keywords are:
    • wintab
    • Your graphics tablet's model name, or it's exact model number.
  • Report a bug against the "Backend: Win32" component if you don't see your problem listed. This requires a login.
  • Example of a really good upstream bug report.
  • If there's a related MyPaint issue, even a closed one, it's helpful to link to the upstream report in a comment so that other people can find it.

The GTK developers will need to know the exact version of libgtk that you're using. If it's a recent MyPaint release, you can find this technical information in the about box,

Reporting bugs in MyPaint

  • Search our Github issue tracker before reporting.
    • Example search: “wintab”.
  • You can report a new bug with the green “New issue” button.
  • See Reporting Bugs for step-by-step information about making a good bug report.
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