Add CombinedBackdropDrawer to support drawing multiple backdrops together

backdrop/src/main/java/com/kyant/backdrop/Backdrop.kt

@@ -33,16 +33,16 @@ fun rememberBackdrop(
 }
 
 @Stable
-class Backdrop internal constructor(
+open class Backdrop internal constructor(
     val graphicsLayer: GraphicsLayer,
     internal val drawLayer: ContentDrawScope.() -> Unit
-) {
+) : BackdropDrawer {
 
     internal var backdropCoordinates: LayoutCoordinates? by mutableStateOf(null)
 
     private var inverseLayerScope: InverseLayerScope? = null
 
-    internal fun DrawScope.drawBackdrop(
+    override fun DrawScope.drawBackdrop(
         density: Density,
         coordinates: LayoutCoordinates,
         layerBlock: (GraphicsLayerScope.() -> Unit)?

backdrop/src/main/java/com/kyant/backdrop/BackdropDrawer.kt

@@ -0,0 +1,15 @@
+package com.kyant.backdrop
+
+import androidx.compose.ui.graphics.GraphicsLayerScope
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.layout.LayoutCoordinates
+import androidx.compose.ui.unit.Density
+
+interface BackdropDrawer {
+
+    fun DrawScope.drawBackdrop(
+        density: Density,
+        coordinates: LayoutCoordinates,
+        layerBlock: (GraphicsLayerScope.() -> Unit)? = null
+    )
+}

backdrop/src/main/java/com/kyant/backdrop/CombinedBackdropDrawer.kt

@@ -0,0 +1,55 @@
+package com.kyant.backdrop
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.Stable
+import androidx.compose.runtime.remember
+import androidx.compose.ui.graphics.GraphicsLayerScope
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.layout.LayoutCoordinates
+import androidx.compose.ui.unit.Density
+
+@Composable
+fun rememberCombinedBackdropDrawer(backdrop1: Backdrop, backdrop2: Backdrop): BackdropDrawer {
+    return remember(backdrop1, backdrop2) {
+        CombinedBackdropDrawer(backdrop1, backdrop2)
+    }
+}
+
+@Composable
+fun rememberCombinedBackdropDrawer(vararg backdrops: Backdrop): BackdropDrawer {
+    return remember(*backdrops) {
+        CombinedBackdropsDrawer(*backdrops)
+    }
+}
+
+@Stable
+private class CombinedBackdropDrawer(
+    val backdrop1: Backdrop,
+    val backdrop2: Backdrop
+) : BackdropDrawer {
+
+    override fun DrawScope.drawBackdrop(
+        density: Density,
+        coordinates: LayoutCoordinates,
+        layerBlock: (GraphicsLayerScope.() -> Unit)?
+    ) {
+        with(backdrop1) { drawBackdrop(density, coordinates, layerBlock) }
+        with(backdrop2) { drawBackdrop(density, coordinates, layerBlock) }
+    }
+}
+
+@Stable
+private class CombinedBackdropsDrawer(
+    vararg val backdrops: Backdrop
+) : BackdropDrawer {
+
+    override fun DrawScope.drawBackdrop(
+        density: Density,
+        coordinates: LayoutCoordinates,
+        layerBlock: (GraphicsLayerScope.() -> Unit)?
+    ) {
+        backdrops.forEach {
+            with(it) { drawBackdrop(density, coordinates, layerBlock) }
+        }
+    }
+}

backdrop/src/main/java/com/kyant/backdrop/DrawBackdropModifier.kt

@@ -40,7 +40,7 @@ internal val DefaultShadow = { Shadow() }
 private val DefaultOnDrawBackdrop: DrawScope.(DrawScope.() -> Unit) -> Unit = { it() }
 
 fun Modifier.drawBackdrop(
-    backdrop: Backdrop,
+    backdrop: BackdropDrawer,
     shape: () -> Shape,
     highlight: (() -> Highlight?)? = DefaultHighlight,
     shadow: (() -> Shadow?)? = DefaultShadow,
@@ -95,7 +95,7 @@ fun Modifier.drawBackdrop(
 }
 
 private class DrawBackdropElement(
-    val backdrop: Backdrop,
+    val backdrop: BackdropDrawer,
     val shapeProvider: BackdropShapeProvider,
     val layerBlock: (GraphicsLayerScope.() -> Unit)?,
     val onDrawBehind: (DrawScope.() -> Unit)?,
@@ -172,7 +172,7 @@ private class DrawBackdropElement(
 }
 
 private class DrawBackdropNode(
-    var backdrop: Backdrop,
+    var backdrop: BackdropDrawer,
     var shapeProvider: BackdropShapeProvider,
     var layerBlock: (GraphicsLayerScope.() -> Unit)?,
     var onDrawBehind: (DrawScope.() -> Unit)?,