geometry: rework `Float::angle_lerp` in the style of `Float::lerp`

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/lib/geometry/angles.nit b/lib/geometry/angles.nit
index f999637..1c8f10d 100644 (file)
--- a/lib/geometry/angles.nit
+++ b/lib/geometry/angles.nit
@@ -31,8 +31,7 @@ redef class Point[N]
        do
                var dx = other.x.to_f - x.to_f
                var dy = other.y.to_f - y.to_f
-               var a = sys.atan2(dy.to_f, dx.to_f)
-               return a
+               return sys.atan2(dy.to_f, dx.to_f)
        end
 end
 
@@ -52,19 +51,21 @@ redef universal Float
                return s
        end
 
-       # Linear interpolation on the arc delimited by `self` and `other` at `p` out of 1.0
+       # Linear interpolation of between the angles `a` and `b`, in radians
        #
        # The result is normalized with `angle_normalize`.
        #
        # ~~~
-       # assert 0.0.angle_lerp(pi, 0.5).is_approx(0.5*pi, 0.0001)
-       # assert 0.0.angle_lerp(pi, 8.5).is_approx(0.5*pi, 0.0001)
-       # assert 0.0.angle_lerp(pi, 7.5).is_approx(-0.5*pi, 0.0001)
+       # assert 0.5.angle_lerp(0.0, pi).is_approx(0.5*pi, 0.0001)
+       # assert 8.5.angle_lerp(0.0, pi).is_approx(0.5*pi, 0.0001)
+       # assert 7.5.angle_lerp(0.0, pi).is_approx(-0.5*pi, 0.0001)
+       # assert 0.5.angle_lerp(0.2, 2.0*pi-0.1).is_approx(0.05, 0.0001)
        # ~~~
-       fun angle_lerp(other, p: Float): Float
+       fun angle_lerp(a, b: Float): Float
        do
-               var d = other - self
-               var a = self + d*p
-               return a.angle_normalize
+               var d = b - a
+               while d > pi do d -= 2.0*pi
+               while d < -pi do d += 2.0*pi
+               return (a + d*self).angle_normalize
        end
 end