lib: intro `Float.lerp` for simple linear interpolation

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

diff --git a/lib/standard/math.nit b/lib/standard/math.nit
index 14c0e40..eec0cf6 100644 (file)
--- a/lib/standard/math.nit
+++ b/lib/standard/math.nit
@@ -195,7 +195,7 @@ redef class Float
        #     assert -1.34.round == -1.0
        #     assert -1.67.round == -2.0
        fun round: Float is extern "round"
-       
+
        # Returns a random `Float` in `[0.0 .. self[`.
        fun rand: Float is extern "kernel_Float_Float_rand_0"
 
@@ -220,6 +220,16 @@ redef class Float
        end
 
        private fun is_inf_extern: Bool is extern "isinf"
+
+       # Linear interpolation between `a` and `b` using `self` as weight
+       #
+       # ~~~
+       # assert  0.0.lerp(0.0, 128.0) == 0.0
+       # assert  0.5.lerp(0.0, 128.0) == 64.0
+       # assert  1.0.lerp(0.0, 128.0) == 128.0
+       # assert -0.5.lerp(0.0, 128.0) == -64.0
+       # ~~~
+       fun lerp(a, b: Float): Float do return (1.0 - self) * a + self * b
 end
 
 redef class Collection[ E ]