lib8: interpolate: implement blend8 API

src/lib8/interpolate.rs

@@ -1,8 +1,13 @@
 use num::PrimInt;
+use std::ops::BitOr;
+
+use rgb::Rgb;
 
 type Fract8 = u8;
+
 pub trait Fract8Ops {
     fn scale8(self, scale: Fract8) -> Self;
+    fn blend8(self, other: Self, scale: Fract8) -> Self;
 }
 
 impl Fract8Ops for u8 {
@@ -10,6 +15,31 @@ impl Fract8Ops for u8 {
         // borrowed from FastLED
         (self as u16 * (1 + scale as u16)).unsigned_shr(8) as u8
     }
+
+    fn blend8(self, other: Self, scale: Fract8) -> Self {
+        ((((self as u16).unsigned_shl(8).bitor(other as u16)) as u16).wrapping_add(other as u16 * scale as u16).wrapping_sub(self as u16 * scale as u16)).unsigned_shr(8) as u8
+    }
+}
+
+impl Fract8Ops for Rgb<u8> {
+    fn scale8(self, scale: Fract8) -> Self {
+        Rgb::new(
+            self.r.scale8(scale),
+            self.g.scale8(scale),
+            self.b.scale8(scale)
+        )
+    }
+
+    fn blend8(self, other: Self, scale: Fract8) -> Self {
+        match (other.r, other.g, other.b) {
+            (0, 0, 0) => self,
+            _ => Rgb::new(
+                self.r.blend8(other.r, scale),
+                self.g.blend8(other.g, scale),
+                self.b.blend8(other.b, scale)
+            )
+        }
+    }
 }
 
 pub fn scale8<T: Fract8Ops>(i: T, scale: Fract8) -> T {