Because not everyone has hours to figure out what each function does.
Come to think of it, I don't actually either...
Signed-off-by: Peter Hutterer <peter.hutte...@who-t.net>
---
src/wcmFilter.c | 34 +++++++++++++++++++++++++++++-----
1 files changed, 29 insertions(+), 5 deletions(-)
diff --git a/src/wcmFilter.c b/src/wcmFilter.c
index 731df4c..ba50877 100644
--- a/src/wcmFilter.c
+++ b/src/wcmFilter.c
@@ -313,12 +313,29 @@ int wcmFilterCoord(WacomCommonPtr common, WacomChannelPtr
pChannel,
return 0; /* lookin' good */
}
-/*****************************************************************************
- * wcmTilt2R -
- * Converts tilt X and Y to rotation, for Intuos4 mouse for now.
- * It can be used for other devices when necessary.
- ****************************************************************************/
+/***
+ * Convert tilt X and Y to rotation
+ *
+ * This function is currently called for the Intuos4 mouse (cursor) tool
+ * only, but it may be used for other devices in the future.
+ *
+ * Method used: rotation angle is calculated through the atan of the tiltx/y
+ * coordinates, then converted to degrees and normalized into the rotation
+ * range (MIN_ROTATION/MAX_ROTATION).
+ * IMPORTANT: calculation inverts direction, the formula to get the target
+ * rotation value in degrees is: 360 - offset - input-angle.
+ *
+ * Example table of return values for an offset of 0, assuming a left-handed
+ * coordinate system:
+ * input 0 degrees: MIN
+ * 90 degrees: MAX - RANGE/4
+ * 180 degrees: RANGE/2
+ * 270 degrees: MIN + RANGE/4
+ *
+ * @param ds The current device state, will be modified to set to the
+ * calculated rotation value.
+ */
void wcmTilt2R(WacomDeviceStatePtr ds)
{
short tilt_x = ds->tiltx;
@@ -327,16 +344,23 @@ void wcmTilt2R(WacomDeviceStatePtr ds)
/* other tilt-enabled devices need to apply round() after this call */
if (tilt_x || tilt_y)
+ /* rotate in the inverse direction, changing CW to CCW
+ * rotation and vice versa */
rotation = ((180.0 * atan2(-tilt_x,tilt_y)) / M_PI) + 180.0;
/* Intuos4 mouse has an (180-5) offset */
ds->rotation = round((360.0 - rotation + 180.0 - 5.0) * 5.0);
ds->rotation %= 1800;
+ /* ds->rotation now normalised into 0 - MAX, but we want MIN - MAX
+ * with 180 degrees (ignoring offset) being at 0 (for whatever
+ * reason we need this) */
if (ds->rotation >= 900)
ds->rotation = 1800 - ds->rotation;
else
ds->rotation = -ds->rotation;
+
+ /* FIXME: shouldn't we reset tilt? */
}
/* vim: set noexpandtab tabstop=8 shiftwidth=8: */
--
1.7.4
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