Cleaning up the code, rewriting the calculations, documentating the steps
taken. It's understandable now. Whoop-dee-doo.
Signed-off-by: Peter Hutterer <peter.hutte...@who-t.net>
---
src/wcmFilter.c | 29 +++++++++++++++++------------
1 files changed, 17 insertions(+), 12 deletions(-)
diff --git a/src/wcmFilter.c b/src/wcmFilter.c
index e020001..d0588b9 100644
--- a/src/wcmFilter.c
+++ b/src/wcmFilter.c
@@ -350,20 +350,25 @@ void wcmTilt2R(WacomDeviceStatePtr ds, double offset)
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;
-
- /* rotation is now in 0 - 360 deg value range.
- normalize into the rotation range and apply the custom offset. */
- ds->rotation = round((360 - rotation + offset) * (MAX_ROTATION_RANGE /
360.0));
+ rotation = ((180.0 * atan2(-tilt_x,tilt_y)) / M_PI);
+
+ /* rotation is now in 0 - 360 deg value range, apply the offset. Use
+ * 360 to avoid getting into negative range, the normalization code
+ * below expects 0...360 */
+ rotation = 360 + rotation - offset;
+
+ /* normalize into the rotation range (0...MAX), then offset by
MIN_ROTATION
+ we used 360 as base offset above, so %= MAX_ROTATION_RANGE brings us
back.
+ Note: we can't use xf86ScaleAxis here because of rounding issues.
+ */
+ ds->rotation = round(rotation * (MAX_ROTATION_RANGE / 360.0));
ds->rotation %= MAX_ROTATION_RANGE;
- /* 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 >= (MIN_ROTATION + MAX_ROTATION_RANGE))
- ds->rotation = MAX_ROTATION_RANGE - ds->rotation; /* wrap
around */
- else
- ds->rotation = -ds->rotation;
+ /* now scale back from 0...MAX to MIN..(MIN+MAX) */
+ ds->rotation = xf86ScaleAxis(ds->rotation,
+ MIN_ROTATION + MAX_ROTATION_RANGE,
+ MIN_ROTATION,
+ MAX_ROTATION_RANGE, 0);
/* FIXME: shouldn't we reset tilt? */
}
--
1.7.4
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