android - Jetpack Compose Canvas BlendMode.SRC_IN 使背景变得透明

Question

我正在尝试使用 BlendMode.SRC_IN 在 PNG 图像（具有透明背景）上添加叠加颜色，但背景变为黑色而不是设置的背景颜色，就好像也屏蔽了背景像素一样。

@Composable
fun Icon(
        fraction: Float,
        image: ImageAsset,
        defaultColor: Color = Color(0xFFEEEEEE),
        progressColor: Color = Color(0xFF888888),
        size: Dp = image.width.dp
) {
    Box(modifier = Modifier.size(size = size)) {
        Canvas(modifier = Modifier.fillMaxSize()) {
            drawImage(
                    image = image,
                    dstSize = IntSize(
                            width = size.toIntPx(),
                            height = size.toIntPx()
                    ),
                    colorFilter = ColorFilter.tint(
                            color = defaultColor
                    ),
                    blendMode = BlendMode.Src
            )
            drawIntoCanvas {
                val paint = Paint().apply {
                    color = progressColor
                    blendMode = BlendMode.SrcIn
                }

                it.restore()
                it.drawRect(
                        rect = Rect(
                                offset = Offset.Zero,
                                size = Size(
                                        width = size.toPx() * fraction,
                                        height = size.toPx()
                                )
                        ),
                        paint = paint
                )
                it.save()
            }
        }
    }
}

这是当我在一个喜欢Icon()的顶部排列多个时的Screen(color = Color.WHITE)样子，

Surface(color = Color.White) {
        Row {
            listOf(
                    R.drawable.anemo,
                    R.drawable.cryo,
                    R.drawable.dendro,
                    R.drawable.electro,
                    R.drawable.geo,
                    R.drawable.hydro,
                    R.drawable.pyro
            ).forEachIndexed { index, imageRes ->
                val from = 100f/7 * index
                val to = 100f/7 * (index + 1)
                val fraction = when {
                    progress > to -> 1f
                    progress > from -> (progress - from)/(to - from)
                    else -> 0f
                }
                Icon(
                        fraction = fraction,
                        image = imageResource(id = imageRes),
                        size = 50.dp
                )
            }
        }
    }

我想要的结果是，

我在这里做错了吗？

这是我正在尝试的Github 存储库。

标签： androidandroid-jetpack-compose

Answer 1

graphicsLayer在我的情况下，我可以通过添加如下修饰符来解决黑色像素应该是透明像素的问题：

Box(
    modifier = Modifier.fillMaxSize()
) {
    Canvas(modifier = Modifier
        .fillMaxSize()
        .graphicsLayer(alpha = 0.99f)
    ) {
        drawRect(
            color = Color.Black,
            size = size,
            blendMode = BlendMode.Xor
        )

        drawCircle(
            color = Color.Black,
            radius = 300f,
            blendMode = BlendMode.Xor
        )
    }
}

没有修饰符：

带修饰符：

我从这里得到了这个想法：https ://gist.github.com/nadewad/14f04c788aea43bd6d31d94cd8100ab5 （请注意drawLayer已重命名为graphicsLayer.