prisma 0.1.1

A color library for both simple and complex color manipulation, intending to be the go to rust color library for most tasks. It can handle conversion between a large number of color models, and can convert into the CIE device independent color spaces. Prisma tries to be easy to use while encouraging correct transformations, making mathematically correct conversions easy without knowing the whole field of color science.
Documentation 
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//! Defines ChannelFormatCast for converting between channel formats
#![cfg_attr(feature = "cargo-clippy", allow(clippy::cast_lossless))]

use angle;
use angle::Angle;
use num_traits;

/// Convert between channel formats
pub trait ChannelFormatCast<Out>: Sized {
    /// Cast the channel scalar type
    fn cast(self) -> Out;
    /// Cast the channel scalar type, optionally rescaling the range
    fn cast_with_rescale(self, _: f64, _: f64) -> Out {
        Self::cast(self)
    }
}

macro_rules! impl_cast_with_rescale_flt_to_int {
    ($from:ty, $to:ty) => {
        /// Cast the channel scalar, optionally rescaling the range
        fn cast_with_rescale(self, min: f64, max: f64) -> $to {
            let range: $from = (max - min) as $from;
            let scaled_self = (self - (min as $from)) / range;
            scaled_self.cast()
        }
    }
}

macro_rules! impl_cast_with_rescale_int_to_flt {
    ($from:ty, $to:ty) => {
        /// Cast the channel scalar, optionally rescaling the range
        fn cast_with_rescale(self, min: f64, max: f64) -> $to {
            let out: $to = self.cast();
            let range = (max - min) as $to;
            out * range + (min as $to)
        }
    }
}

impl ChannelFormatCast<u8> for u8 {
    fn cast(self) -> u8 {
        self
    }
}
impl ChannelFormatCast<u16> for u8 {
    fn cast(self) -> u16 {
        (self as u16) * 0x0101_u16
    }
}
impl ChannelFormatCast<u32> for u8 {
    fn cast(self) -> u32 {
        (self as u32) * 0x01010101_u32
    }
}
impl ChannelFormatCast<u64> for u8 {
    fn cast(self) -> u64 {
        (self as u64) * 0x0101010101010101_u64
    }
}
impl ChannelFormatCast<f32> for u8 {
    fn cast(self) -> f32 {
        (self as f32) / (0xFF as f32)
    }
    impl_cast_with_rescale_int_to_flt!(u8, f32);
}
impl ChannelFormatCast<f64> for u8 {
    fn cast(self) -> f64 {
        (self as f64) / (0xFF as f64)
    }
    impl_cast_with_rescale_int_to_flt!(u8, f64);
}

impl ChannelFormatCast<u8> for u16 {
    fn cast(self) -> u8 {
        (self >> 8) as u8
    }
}
impl ChannelFormatCast<u16> for u16 {
    fn cast(self) -> u16 {
        self
    }
}
impl ChannelFormatCast<u32> for u16 {
    fn cast(self) -> u32 {
        (self as u32) * 0x00010001_u32
    }
}
impl ChannelFormatCast<u64> for u16 {
    fn cast(self) -> u64 {
        (self as u64) * 0x0001000100010001_u64
    }
}
impl ChannelFormatCast<f32> for u16 {
    fn cast(self) -> f32 {
        (self as f32) / (0xFFFF as f32)
    }
    impl_cast_with_rescale_int_to_flt!(u16, f32);
}
impl ChannelFormatCast<f64> for u16 {
    fn cast(self) -> f64 {
        (self as f64) / (0xFFFF as f64)
    }
    impl_cast_with_rescale_int_to_flt!(u16, f64);
}

impl ChannelFormatCast<u8> for u32 {
    fn cast(self) -> u8 {
        (self >> 24) as u8
    }
}
impl ChannelFormatCast<u16> for u32 {
    fn cast(self) -> u16 {
        (self >> 16) as u16
    }
}
impl ChannelFormatCast<u32> for u32 {
    fn cast(self) -> u32 {
        self
    }
}
impl ChannelFormatCast<u64> for u32 {
    fn cast(self) -> u64 {
        (self as u64) * 0x0000000100000001_u64
    }
}
impl ChannelFormatCast<f32> for u32 {
    fn cast(self) -> f32 {
        (self as f32) / (0xFFFFFFFF_u32 as f32)
    }
    impl_cast_with_rescale_int_to_flt!(u32, f32);
}
impl ChannelFormatCast<f64> for u32 {
    fn cast(self) -> f64 {
        (self as f64) / (0xFFFFFFFF_u32 as f64)
    }
    impl_cast_with_rescale_int_to_flt!(u32, f64);
}

impl ChannelFormatCast<u8> for u64 {
    fn cast(self) -> u8 {
        (self >> 56) as u8
    }
}
impl ChannelFormatCast<u16> for u64 {
    fn cast(self) -> u16 {
        (self >> 48) as u16
    }
}
impl ChannelFormatCast<u32> for u64 {
    fn cast(self) -> u32 {
        (self >> 32) as u32
    }
}
impl ChannelFormatCast<u64> for u64 {
    fn cast(self) -> u64 {
        self
    }
}
impl ChannelFormatCast<f32> for u64 {
    fn cast(self) -> f32 {
        (self as f32) / (0xFFFFFFFFFFFFFFFF_u64 as f32)
    }
    impl_cast_with_rescale_int_to_flt!(u64, f32);
}
impl ChannelFormatCast<f64> for u64 {
    fn cast(self) -> f64 {
        (self as f64) / (0xFFFFFFFFFFFFFFFF_u64 as f64)
    }
    impl_cast_with_rescale_int_to_flt!(u64, f64);
}

impl ChannelFormatCast<u8> for f32 {
    fn cast(self) -> u8 {
        // For u8, we want some extra precision, so multiply by just under 256.
        // This will make more than just 1.0 map to 255.
        (self * 255.99_f32).floor() as u8
    }
    impl_cast_with_rescale_flt_to_int!(f32, u8);
}
impl ChannelFormatCast<u16> for f32 {
    fn cast(self) -> u16 {
        (self * (0xFFFF_u32 as f32)) as u16
    }
    impl_cast_with_rescale_flt_to_int!(f32, u16);
}
impl ChannelFormatCast<u32> for f32 {
    fn cast(self) -> u32 {
        (self * (0xFFFFFFFF_u32 as f32)) as u32
    }
    impl_cast_with_rescale_flt_to_int!(f32, u32);
}
impl ChannelFormatCast<u64> for f32 {
    fn cast(self) -> u64 {
        (self * (0xFFFFFFFFFFFFFFFF_u64 as f32)) as u64
    }
    impl_cast_with_rescale_flt_to_int!(f32, u64);
}
impl ChannelFormatCast<f32> for f32 {
    fn cast(self) -> f32 {
        self
    }
}
impl ChannelFormatCast<f64> for f32 {
    fn cast(self) -> f64 {
        self as f64
    }
}

impl ChannelFormatCast<u8> for f64 {
    fn cast(self) -> u8 {
        // For u8, we want some extra precision, so multiply by just under 256.
        // This will make more than just 1.0 map to 255.
        (self * 255.99_f64).floor() as u8
    }
    impl_cast_with_rescale_flt_to_int!(f64, u8);
}
impl ChannelFormatCast<u16> for f64 {
    fn cast(self) -> u16 {
        (self * (0xFFFF_u32 as f64)) as u16
    }
    impl_cast_with_rescale_flt_to_int!(f64, u16);
}
impl ChannelFormatCast<u32> for f64 {
    fn cast(self) -> u32 {
        (self * (0xFFFFFFFF_u32 as f64)) as u32
    }
    impl_cast_with_rescale_flt_to_int!(f64, u32);
}
impl ChannelFormatCast<u64> for f64 {
    fn cast(self) -> u64 {
        (self * (0xFFFFFFFFFFFFFFFF_u64 as f64)) as u64
    }
    impl_cast_with_rescale_flt_to_int!(f64, u64);
}
impl ChannelFormatCast<f32> for f64 {
    fn cast(self) -> f32 {
        self as f32
    }
}
impl ChannelFormatCast<f64> for f64 {
    fn cast(self) -> f64 {
        self
    }
}

macro_rules! impl_channel_format_cast_for_angle {
    ($angle: ident) => {
        impl<T, A, U> ChannelFormatCast<A> for angle::$angle<T>
        where
            A: Angle<Scalar = U>,
            T: num_traits::Float + ChannelFormatCast<U>,
            U: num_traits::Float,
        {
            fn cast(self) -> A {
                let scalar: U =
                    self.0.cast() * (A::period() / num_traits::cast(Self::period()).unwrap());
                A::new(scalar)
            }
        }
    };
}

impl_channel_format_cast_for_angle!(Deg);
impl_channel_format_cast_for_angle!(Rad);
impl_channel_format_cast_for_angle!(Turns);
impl_channel_format_cast_for_angle!(ArcMinutes);
impl_channel_format_cast_for_angle!(ArcSeconds);