android - Jetpack Compose 中的图像渐变

Question

这是我的组件:

@Composable
fun Cover(
    name: String,
    imageRes: Int,
    modifier: Modifier = Modifier.padding(16.dp, 8.dp)
) {
    Box(modifier) {
        Card(
            shape = RoundedCornerShape(4.dp),
            backgroundColor = MaterialTheme.colors.secondary,
            elevation = 4.dp
        ) {
            Stack {
                Image(
                    imageResource(imageRes),
                    modifier = Modifier
                        .gravity(Alignment.Center)
                        .aspectRatio(2f),
                    contentScale = ContentScale.Crop,
                )

                Text(
                    text = name,
                    modifier = Modifier
                        .gravity(Alignment.BottomStart)
                        .padding(8.dp),
                    style = MaterialTheme.typography.h6
                )
            }
        }
    }
}

这是它的外观:

我想在 Image 上显示深色渐变在 Text 后面使文本易于阅读。我想我必须使用 LinearGradient或 RadialGradient但由于缺乏文档，我无法做到。
编辑:This是我想要做的，但使用 Jetpack Compose。

Answer 1

与 1.0.0你可以使用类似的东西:

var sizeImage by remember { mutableStateOf(IntSize.Zero) }

val gradient = Brush.verticalGradient(
    colors = listOf(Color.Transparent, Color.Black),
    startY = sizeImage.height.toFloat()/3,  // 1/3
    endY = sizeImage.height.toFloat()
)

Box(){
    Image(painter = painterResource(id = R.drawable.banner),
        contentDescription = "",
    modifier = Modifier.onGloballyPositioned {
        sizeImage = it.size
    })
    Box(modifier = Modifier.matchParentSize().background(gradient))
}

原来的:

后:

您还可以将渐变应用到 Image()使用 .drawWithCache 修饰符和 onDrawWithContent 允许开发人员在布局内容之前或之后进行绘制。

  Image(painter = painterResource(id = R.drawable.conero),
      contentDescription = "",
      modifier = Modifier.drawWithCache {
          val gradient = Brush.verticalGradient(
              colors = listOf(Color.Transparent, Color.Black),
              startY = size.height/3,
              endY = size.height
          )
          onDrawWithContent {
              drawContent()
              drawRect(gradient,blendMode = BlendMode.Multiply)
          }
      }
  )