[gtk+] win32: Fix tilt from Wintab devices

[Ignacio Casal Quinteiro <icq src gnome org>]

commit 9e3bd03d3ec1de295d2fb2e2eb7499b4d4851859
Author: Andrew Chadwick <a t chadwick gmail com>
Date:   Sat Nov 19 18:34:29 2016 +0000

    win32: Fix tilt from Wintab devices
    
    Move the orientation sanity-checks into the packet decode func.
    Rationale: the packet handling func may otherwise read beyond the end of
    device->last_axis_data.
    
    Also expand them to cope with my test Huion's weird reporting.
    
    Also correct the azimuth angle to align with GDK's presentation.
    
    Most importantly, fix annoying comment typo.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=774265

 gdk/win32/gdkdevicemanager-win32.c |   34 +++++++++++++++++++++++++---------
 1 files changed, 25 insertions(+), 9 deletions(-)
---
diff --git a/gdk/win32/gdkdevicemanager-win32.c b/gdk/win32/gdkdevicemanager-win32.c
index 9f1f391..f88dab7 100644
--- a/gdk/win32/gdkdevicemanager-win32.c
+++ b/gdk/win32/gdkdevicemanager-win32.c
@@ -613,17 +613,12 @@ wintab_init_check (GdkDeviceManagerWin32 *device_manager)
               num_axes++;
             }
 
-          /* The wintab driver for the Wacom ArtPad II reports
-           * PK_ORIENTATION in CSR_PKTDATA, but the tablet doesn't
-           * actually sense tilt. Catch this by noticing that the
-           * orientation axis's azimuth resolution is zero.
-           */
-          if ((device->pktdata & PK_ORIENTATION) && axis_or[0].axResolution == 0)
+          if (device->pktdata & PK_ORIENTATION)
             {
               device->orientation_axes[0] = axis_or[0];
               device->orientation_axes[1] = axis_or[1];
 
-              /* Wintab gives us aximuth and altitude, which
+              /* Wintab gives us azimuth and altitude, which
                * we convert to x and y tilt in the -1000..1000 range
                */
               _gdk_device_add_axis (GDK_DEVICE (device),
@@ -805,11 +800,32 @@ decode_tilt (gint   *axis_data,
 {
   double az, el;
 
-  /* As I don't have a tilt-sensing tablet,
-   * I cannot test this code.
+  /* The wintab driver for the Wacom ArtPad II reports
+   * PK_ORIENTATION in CSR_PKTDATA, but the tablet doesn't
+   * actually sense tilt. Catch this by noticing that the
+   * orientation axis's azimuth resolution is zero.
+   *
+   * The same is true of the Huion H610PRO, but in this case
+   * it's the altitude resolution that's zero. GdkEvents with
+   * sensible tilts will need both, so only add the GDK tilt axes
+   * if both wintab axes are going to be well-behaved in use.
+   */
+  if ((axes == NULL) || (axis_data == NULL) ||
+      (axes[0].axResolution == 0) ||
+      (axes[1].axResolution == 0))
+    {
+      axis_data[0] = 0;
+      axis_data[1] = 0;
+      return;
+    }
+
+  /*
+   * Tested with a Wacom Intuos 5 touch M (PTH-650) + Wacom drivers 6.3.18-5.
+   * Wintab's reference angle leads gdk's by 90 degrees.
    */
   az = TWOPI * packet->pkOrientation.orAzimuth /
     (axes[0].axResolution / 65536.);
+  az -= G_PI / 2;
   el = TWOPI * packet->pkOrientation.orAltitude /
     (axes[1].axResolution / 65536.);