Metal每日分享，灵魂出窍滤镜效果

// 灵魂出窍滤镜
let filter = C7SoulOut.init(soul: 0.7)
// 方案1:
let dest = BoxxIO.init(element: originImage, filter: filter)
ImageView.image = try? dest.output()
dest.filters.forEach {
    NSLog("%@", "\($0.parameterDescription)")
}
// 方案2:
ImageView.image = try? originImage.make(filter: filter)
// 方案3:
ImageView.image = originImage ->> filter

/// 灵魂出窍效果
public struct C7SoulOut: C7FilterProtocol {
    public static let soulRange: ParameterRange<Float, Self> = .init(min: 0.0, max: 1.0, value: 0.5)
    /// The adjusted soul, from 0.0 to 1.0, with a default of 0.5
    public var soul: Float = soulRange.value
    public var maxScale: Float = 1.5
    public var maxAlpha: Float = 0.5
    public var modifier: Modifier {
        return .compute(kernel: "C7SoulOut")
    }
    public var factors: [Float] {
        return [soul, maxScale, maxAlpha]
    }
    public init(soul: Float = soulRange.value, maxScale: Float = 1.5, maxAlpha: Float = 0.5) {
        self.soul = soul
        self.maxScale = maxScale
        self.maxAlpha = maxAlpha
    }
}

kernel void C7SoulOut(texture2d<half, access::write> outputTexture [[texture(0)]],
                      texture2d<half, access::sample> inputTexture [[texture(1)]],
                      constant float *soulPointer [[buffer(0)]],
                      constant float *maxScalePointer [[buffer(1)]],
                      constant float *maxAlphaPointer [[buffer(2)]],
                      uint2 grid [[thread_position_in_grid]]) {
    constexpr sampler quadSampler(mag_filter::linear, min_filter::linear);
    const half4 inColor = inputTexture.read(grid);
    const float x = float(grid.x) / outputTexture.get_width();
    const float y = float(grid.y) / outputTexture.get_height();
    const half soul = half(*soulPointer);
    const half maxScale = half(*maxScalePointer);
    const half maxAlpha = half(*maxAlphaPointer);
    const half alpha = maxAlpha * (1.0h - soul);
    const half scale = 1.0h + (maxScale - 1.0h) * soul;
    const half soulX = 0.5h + (x - 0.5h) / scale;
    const half soulY = 0.5h + (y - 0.5h) / scale;
    // 最终色 = 基色 * (1 - a) + 混合色 * a
    const half4 soulMask = inputTexture.sample(quadSampler, float2(soulX, soulY));
    const half4 outColor = inColor * (1.0h - alpha) + soulMask * alpha;
    outputTexture.write(outColor, grid);
}