colors.hsv: adding rgba>hsva.

basis/colors/hsv/hsv.factor

@@ -1,12 +1,17 @@
 ! Copyright (C) 2008 Eduardo Cavazos.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: colors kernel combinators math math.functions accessors ;
+USING: accessors arrays colors combinators kernel locals math
+math.functions sequences sorting ;
 IN: colors.hsv
 
 ! h [0,360)
 ! s [0,1]
 ! v [0,1]
-TUPLE: hsva < color { hue read-only } { saturation read-only } { value read-only } { alpha read-only } ;
+TUPLE: hsva < color
+{ hue read-only }
+{ saturation read-only }
+{ value read-only }
+{ alpha read-only } ;
 
 C: <hsva> hsva
 
@@ -36,3 +41,17 @@ M: hsva >rgba ( hsva -- rgba )
             { 5 [ [ value>> ] [ p ] [ q ] tri ] }
         } case
     ] [ alpha>> ] bi <rgba> ;
+
+:: rgba>hsva ( rgba -- hsva )
+    rgba >rgba-components :> ( r g b a )
+    r g b 3array natural-sort first3 :> ( z y x )
+    x z = x zero? or [ 0 0 x a <hsva> ] [
+        {
+            { [ r x = g z = and ] [ 5 x b - x z - / + ] }
+            { [ r x = g z > and ] [ 1 x g - x z - / - ] }
+            { [ g x = b z = and ] [ 1 x r - x z - / + ] }
+            { [ g x = b z > and ] [ 3 x b - x z - / - ] }
+            { [ b x = r z = and ] [ 3 x g - x z - / + ] }
+            { [ b x = r z > and ] [ 5 x r - x z - / - ] }
+        } cond 6 / 360 * x z - x / x a <hsva>
+    ] if ;