基于rust的RGBA颜色混合

一般采用以下脚本。

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Pixel {
    pub r: u8,
    pub g: u8,
    pub b: u8,
    pub a: u8,
}

impl Pixel {
    pub fn blend(p1: Pixel, p2: Pixel) -> Pixel {
        let a1 = p1.a as u32;
        let a2 = p2.a as u32;

        let a3 = a2 + (a1 * (255 - a2) >> 8);
        let x = a3 - a1;

        let r = ((p1.r as u32 * a1 + p2.r as u32 * x) / a3) as u8;
        let g = ((p1.g as u32 * a1 + p2.g as u32 * x) / a3) as u8;
        let b = ((p1.b as u32 * a1 + p2.b as u32 * x) / a3) as u8;
        let a = a3 as u8;

        Pixel { r, g, b, a }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn basic() {
        let p1 = Pixel { r: 255, g: 0, b: 0, a: 128 };
        let p2 = Pixel { r: 0, g: 255, b: 0, a: 255 };
        let blended = Pixel::blend(p1, p2);
        println!("{:?}", blended);
    }
}

若透明像素较多，考虑以下脚本。

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Pixel {
    pub r: u8,
    pub g: u8,
    pub b: u8,
    pub a: u8,
}

impl Pixel {
    pub fn blend(p1: Pixel, p2: Pixel) -> Pixel {
        let a1 = p1.a as u32;
        let a2 = p2.a as u32;

        if a1 == 0 { return p2; }
        if a2 == 0 { return p1; }

        let a3 = a2 + (a1 * (255 - a2) >> 8);
        let x = a3 - a1;

        let r = ((p1.r as u32 * a1 + p2.r as u32 * x) / a3) as u8;
        let g = ((p1.g as u32 * a1 + p2.g as u32 * x) / a3) as u8;
        let b = ((p1.b as u32 * a1 + p2.b as u32 * x) / a3) as u8;
        let a = a3 as u8;

        Pixel { r, g, b, a }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn basic() {
        let p1 = Pixel { r: 255, g: 0, b: 0, a: 128 };
        let p2 = Pixel { r: 0, g: 255, b: 0, a: 255 };
        let blended = Pixel::blend(p1, p2);
        println!("{:?}", blended);
    }
}