Jetpack compose BlendMode.Xor demo

gistfile1.txt

@Composable
fun foo() {
    Canvas(Modifier
        .fillMaxSize()
        .wrapContentSize(Alignment.Center)
        .preferredSize(120.dp, 120.dp)
        // Provide a slight opacity to for compositing into an 
        // offscreen buffer to ensure blend modes are applied to empty pixel information
        // By default any alpha != 1.0f will use a compositing layer by default
        .drawLayer(alpha = 0.99f)
    ) {
        val radius = size.minDimension / 4
        drawCircle(
            Color.Red,
            center = Offset(center.x - radius / 2, center.y),
            radius = radius,
            blendMode = BlendMode.Xor
        )

        drawCircle(
            Color.Red,
            center = Offset(center.x + radius / 2, center.y),
            radius = radius,
            blendMode = BlendMode.Xor
        )
    }
}

How did you know that the opacity should be .99?