This is the best explanation I can come up with, but it seems to hold true for my example values.
Signed-off-by: Peter Hutterer <[email protected]> --- dix/ptrveloc.c | 12 ++++++++++-- 1 files changed, 10 insertions(+), 2 deletions(-) diff --git a/dix/ptrveloc.c b/dix/ptrveloc.c index 50ad22a..fafbbb0 100644 --- a/dix/ptrveloc.c +++ b/dix/ptrveloc.c @@ -483,8 +483,16 @@ DoGetDirection(int dx, int dy){ #else r = atan2(dy, dx); #endif - /* find direction. We avoid r to become negative, - * since C has no well-defined modulo for such cases. */ + /* find direction. + * + * Add 360° to avoid r become negative since C has no well-defined + * modulo for such cases. Then divide by 45° to get the octant number, + * e.g. 0 <= r <= 1 is [0-45]° + * 1 <= r <= 2 is [45-90]° + * etc. + * But we add extra 90° to match up with our N, S, etc. defines up + * there, rest stays the same. + */ r = (r+(M_PI*2.5))/(M_PI/4); /* this intends to flag 2 directions (45 degrees), * except on very well-aligned mickeys. */ -- 1.7.4.4 _______________________________________________ [email protected]: X.Org development Archives: http://lists.x.org/archives/xorg-devel Info: http://lists.x.org/mailman/listinfo/xorg-devel
