Simpler scaling

src/Style/Scale.elm

@@ -11,16 +11,21 @@ Then, when setting font sizes you can use:
 
     Font.size (scaled 1) -- results in 16
 
-    Font.size (scaled 2) -- 16 * (1.618 ^ 2) results in 25.8
+    Font.size (scaled 2) -- 16 * 1.618 results in 25.8
+
+    Font.size (scaled 4) -- 16 * 1.618 ^ (4 - 1) results in 67.8
 
 We can also provide negative numbers to scale below 16px.
 
+    Font.size (scaled -1) -- 16 * 1.618 ^ (-1) results in 9.9
+
 @docs modular, roundedModular
 
 -}
 
 
-{-| -}
+{-| Given a normal size and a ratio, returns a function which takes a scale parameter and returns a new size
+-}
 modular : Float -> Float -> Int -> Float
 modular normal ratio fontScale =
     resize normal ratio fontScale
@@ -38,25 +43,9 @@ roundedModular normal ratio =
 
 resize : Float -> Float -> Int -> Float
 resize normal ratio scale =
-    if scale == 0 || scale == 1 then
+    if scale == 0 then
         normal
     else if scale < 0 then
-        shrink ratio (scale * -1) normal
-    else
-        grow ratio (scale - 1) normal
-
-
-grow : Float -> Int -> Float -> Float
-grow ratio i size =
-    if i <= 0 then
-        size
-    else
-        grow ratio (i - 1) (size * ratio)
-
-
-shrink : Float -> Int -> Float -> Float
-shrink ratio i size =
-    if i <= 0 then
-        size
+        normal * ratio ^ (toFloat scale)
     else
-        shrink ratio (i - 1) (size / ratio)
+        normal * ratio ^ (toFloat scale - 1)

tests/ScaleTest.elm

@@ -0,0 +1,47 @@
+module ScaleTest exposing (..)
+
+import Expect
+import Style.Scale exposing (roundedModular)
+import Fuzz exposing (intRange, floatRange)
+import Test exposing (..)
+
+
+fakeModular : Float -> Float -> Int -> Float
+fakeModular a b n =
+    if n == 0 then
+        a
+    else if n < 0 then
+        a * b ^ (toFloat n)
+    else
+        a * b ^ (toFloat n - 1)
+
+
+fakeRounded a b =
+    toFloat << round << fakeModular a b
+
+
+expecter : Float -> Float -> Int -> Expect.Expectation
+expecter a b n =
+    (fakeRounded a b n == roundedModular a b n)
+        |> Expect.true "implementations don't match"
+
+
+normal =
+    floatRange 1 200
+
+
+ratio =
+    floatRange 1 3
+
+
+exponent =
+    intRange -10 10
+
+
+suite =
+    fuzz3
+        normal
+        ratio
+        exponent
+        "Check that the implementation matches my implementation"
+        expecter