Add new backdrop module

backdrop/.gitignore

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+/build

backdrop/build.gradle.kts

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+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+plugins {
+    alias(libs.plugins.android.library)
+    alias(libs.plugins.kotlin.android)
+    alias(libs.plugins.kotlin.compose)
+    id("dev.shreyaspatil.compose-compiler-report-generator")
+}
+
+android {
+    namespace = "com.kyant.backdrop"
+    compileSdk = 36
+    buildToolsVersion = "36.0.0"
+
+    defaultConfig {
+        minSdk = 21
+        consumerProguardFiles("consumer-rules.pro")
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_21
+        targetCompatibility = JavaVersion.VERSION_21
+    }
+    kotlin {
+        compilerOptions {
+            jvmTarget = JvmTarget.JVM_21
+            freeCompilerArgs.addAll(
+                "-jvm-default=no-compatibility",
+            )
+        }
+    }
+    buildFeatures {
+        compose = true
+    }
+}
+
+dependencies {
+    implementation(libs.androidx.compose.foundation)
+    implementation(libs.androidx.compose.ui)
+    implementation(libs.androidx.compose.ui.graphics)
+}

backdrop/proguard-rules.pro

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+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

backdrop/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+</manifest>

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

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+package com.kyant.backdrop
+
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.layout.LayoutCoordinates
+
+fun Modifier.backdrop(backdrop: Backdrop): Modifier {
+    val element = backdrop.element
+    return if (element != null) {
+        this then element
+    } else {
+        this
+    }
+}
+
+interface Backdrop {
+
+    val element: Modifier.Element?
+
+    fun DrawScope.drawChild(coordinates: LayoutCoordinates)
+}

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

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+package com.kyant.backdrop
+
+import androidx.compose.ui.graphics.drawscope.DrawScope
+
+sealed interface BackdropDrawScope : DrawScope {
+
+    fun drawBackdrop()
+}
+
+class SimpleBackdropDrawScope(
+    val drawScope: DrawScope,
+    val onDrawBackdrop: DrawScope.() -> Unit
+) : BackdropDrawScope, DrawScope by drawScope {
+
+    override fun drawBackdrop() {
+        onDrawBackdrop()
+    }
+}

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

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+package com.kyant.backdrop
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.Stable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.drawscope.ContentDrawScope
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.graphics.drawscope.translate
+import androidx.compose.ui.graphics.isSpecified
+import androidx.compose.ui.graphics.layer.GraphicsLayer
+import androidx.compose.ui.graphics.layer.drawLayer
+import androidx.compose.ui.graphics.nativeCanvas
+import androidx.compose.ui.graphics.rememberGraphicsLayer
+import androidx.compose.ui.graphics.toArgb
+import androidx.compose.ui.layout.LayoutCoordinates
+import androidx.compose.ui.layout.positionOnScreen
+import androidx.compose.ui.node.DrawModifierNode
+import androidx.compose.ui.node.GlobalPositionAwareModifierNode
+import androidx.compose.ui.node.ModifierNodeElement
+import androidx.compose.ui.platform.InspectorInfo
+
+@Composable
+fun rememberLayerBackdrop(backgroundColor: Color?): LayerBackdrop {
+    val graphicsLayer = rememberGraphicsLayer()
+    return remember(graphicsLayer, backgroundColor) {
+        LayerBackdrop(
+            graphicsLayer = graphicsLayer,
+            backgroundColor = backgroundColor
+        )
+    }
+}
+
+@Stable
+class LayerBackdrop(
+    val graphicsLayer: GraphicsLayer,
+    val backgroundColor: Color?
+) : Backdrop {
+
+    override val element: Modifier.Element?
+        get() = LayerBackdropElement(this)
+
+    var backdropPosition: Offset by mutableStateOf(Offset.Zero)
+
+    override fun DrawScope.drawChild(coordinates: LayoutCoordinates) {
+        val position = coordinates.positionOnScreen() - backdropPosition
+        translate(-position.x, -position.y) {
+            if (backgroundColor != null && backgroundColor.isSpecified) {
+                drawContext.canvas.nativeCanvas.drawColor(backgroundColor.toArgb())
+            }
+            drawLayer(graphicsLayer)
+        }
+    }
+}
+
+private class LayerBackdropElement(
+    val backdrop: LayerBackdrop
+) : ModifierNodeElement<LayerBackdropNode>() {
+
+    override fun create(): LayerBackdropNode {
+        return LayerBackdropNode(backdrop = backdrop)
+    }
+
+    override fun update(node: LayerBackdropNode) {
+        node.update(backdrop = backdrop)
+    }
+
+    override fun InspectorInfo.inspectableProperties() {
+        name = "layerBackdrop"
+        properties["backdrop"] = backdrop
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other !is LayerBackdropElement) return false
+
+        if (backdrop != other.backdrop) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        return backdrop.hashCode()
+    }
+}
+
+private class LayerBackdropNode(
+    var backdrop: LayerBackdrop
+) : DrawModifierNode, GlobalPositionAwareModifierNode, Modifier.Node() {
+
+    override val shouldAutoInvalidate: Boolean = false
+
+    override fun ContentDrawScope.draw() {
+        drawContent()
+
+        backdrop.graphicsLayer.record {
+            backdrop.backgroundColor?.let { drawRect(it) }
+            this@draw.drawContent()
+        }
+    }
+
+    override fun onGloballyPositioned(coordinates: LayoutCoordinates) {
+        if (coordinates.isAttached) {
+            backdrop.backdropPosition = coordinates.positionOnScreen()
+        }
+    }
+
+    fun update(backdrop: LayerBackdrop) {
+        this.backdrop = backdrop
+    }
+}