luminanceToAlpha()

Return Value 戻り値

A view with the luminance to alpha effect applied.

Discussion 議論

Use this modifier to create a semitransparent mask, with the opacity of each part of the modified view controlled by the luminance of the corresponding part of the original view. Regions of lower luminance become more transparent, while higher luminance yields greater opacity.

In particular, the modifier maps the red, green, and blue components of each input pixel’s color to a grayscale value, and that value becomes the alpha component of a black pixel in the output. This modifier produces an effect that’s equivalent to using the feColorMatrix filter primitive with the luminanceToAlpha type attribute, as defined by the Scalable Vector Graphics (SVG) 2 specification.

The example below defines a Palette view as a series of rectangles, each composed as a Color with a particular white value, and then displays two versions of the palette over a blue background:

struct Palette: View {
    var body: some View {
        HStack(spacing: 0) {
            ForEach(0..<10) { index in
                Color(white: Double(index) / Double(9))
                    .frame(width: 20, height: 40)
            }
        }
    }
}


struct LuminanceToAlphaExample: View {
    var body: some View {
        VStack(spacing: 20) {
            Palette()


            Palette()
                .luminanceToAlpha()
        }
        .padding()
        .background(.blue)
    }
}

The unmodified version of the palette contains rectangles that range from solid black to solid white, thus with increasing luminance. The second version of the palette, which has the luminanceToAlpha() modifier applied, allows the background to show through in an amount that corresponds inversely to the luminance of the input.