message: Optimize Rgba blend
diff: @@ -731,6 +731,14 @@ impl<T: Primitive> Blend for Rgba<T> {
  fn blend(&mut self, other: &Rgba<T>) {
  // http://stackoverflow.com/questions/7438263/alpha-compositing-algorithm-blend-modes#answer-11163848
  + if other.0[3].is_zero() {
  + return;
  + }
  + if other.0[3].to_i32().unwrap() == 255 {
  + *self = *other;
  + return;
  + }
  +
  // First, as we don't know what type our pixel is, we have to convert to floats between 0.0 and 1.0
  let max_t = T::DEFAULT_MAX_VALUE;
  let max_t = max_t.to_f32().unwrap();
  