lib8: interpolate: optimize some edge cases for blending

src/lib8/interpolate.rs

@@ -12,12 +12,21 @@ pub trait Fract8Ops {
 
 impl Fract8Ops for u8 {
     fn scale8(self, scale: Fract8) -> Self {
+        match scale {
+            0 => 0,
+            255 => self,
+            _ => 
                 // 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
+        match scale {
+            0 => self,
+            255 => other,
+            _ => ((((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
+        }
     }
 }
 
@@ -31,7 +40,10 @@ impl Fract8Ops for Rgb<u8> {
     }
 
     fn blend8(self, other: Self, scale: Fract8) -> Self {
-        match (other.r, other.g, other.b) {
+        match scale {
+            0 => self,
+            255 => other,
+            _ => match (other.r, other.g, other.b) {
                 (0, 0, 0) => self,
                 _ => Rgb::new(
                     self.r.blend8(other.r, scale),
@@ -40,6 +52,7 @@ impl Fract8Ops for Rgb<u8> {
                 )
             }
         }
+    }
 }
 
 pub fn scale8<T: Fract8Ops>(i: T, scale: Fract8) -> T {