JetBrains · eymar · Jul 7, 2023 · Jul 7, 2023 · Jul 7, 2023
diff --git a/compose/mpp/demo/src/jsMain/kotlin/androidx/compose/mpp/demo/main.js.kt b/compose/mpp/demo/src/jsMain/kotlin/androidx/compose/mpp/demo/main.js.kt
@@ -1,16 +1,19 @@
 package androidx.compose.mpp.demo
 
 import androidx.compose.runtime.remember
+import androidx.compose.ui.ExperimentalComposeUiApi
+import androidx.compose.ui.window.CanvasBasedWindow
 import androidx.compose.ui.window.Window
 import kotlinx.browser.document
 import org.jetbrains.skiko.GenericSkikoView
 import org.jetbrains.skiko.SkiaLayer
 import org.jetbrains.skiko.wasm.onWasmReady
 import org.w3c.dom.HTMLCanvasElement
 
+@OptIn(ExperimentalComposeUiApi::class)
 fun main() {
     onWasmReady {
-        Window("Compose/JS sample") {
+        CanvasBasedWindow("Compose/JS sample", canvasElementId = "canvas1") {
             val app = remember { App() }
             app.Content()
         }

diff --git a/compose/mpp/demo/src/jsMain/resources/index.html b/compose/mpp/demo/src/jsMain/resources/index.html
@@ -5,12 +5,21 @@
     <title>compose multiplatform web demo</title>
     <script src="skiko.js"> </script>
     <link type="text/css" rel="stylesheet" href="styles.css">
+    <style>
+        html, body {
+            width: 100%;
+            height: 100%;
+            margin: 0;
+            padding: 0;
+            overflow: hidden;
+        }
+    </style>
 </head>
 
 <body>
     <h1>compose multiplatform web demo</h1>
     <div>
-        <canvas id="ComposeTarget" width="800" height="600"></canvas>
+        <canvas id="canvas1" width="800" height="600"></canvas>
     </div>
     <script src="demo.js"> </script>
 </body>

diff --git a/compose/ui/ui/src/jsWasmMain/kotlin/androidx/compose/ui/window/ComposeWindow.js.kt b/compose/ui/ui/src/jsWasmMain/kotlin/androidx/compose/ui/window/ComposeWindow.js.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 The Android Open Source Project
+ * Copyright 2023 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,19 +17,28 @@
 package androidx.compose.ui.window
 
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.ui.ExperimentalComposeUiApi
 import androidx.compose.ui.createSkiaLayer
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.native.ComposeLayer
 import androidx.compose.ui.platform.JSTextInputService
 import androidx.compose.ui.platform.Platform
 import androidx.compose.ui.platform.ViewConfiguration
 import androidx.compose.ui.unit.Density
+import androidx.compose.ui.unit.IntSize
 import androidx.compose.ui.unit.dp
 import kotlinx.browser.document
 import kotlinx.browser.window
+import kotlinx.coroutines.isActive
 import org.w3c.dom.HTMLCanvasElement
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.channels.Channel.Factory.CONFLATED
+import kotlinx.coroutines.delay
 
-internal actual class ComposeWindow actual constructor() {
+internal actual class ComposeWindow(val canvasId: String)  {
+
+    actual constructor(): this(defaultCanvasElementId)
 
     private val density: Density = Density(
         density = window.devicePixelRatio.toFloat(),
@@ -53,14 +62,22 @@ internal actual class ComposeWindow actual constructor() {
         input = jsTextInputService.input
     )
 
-    // TODO: generalize me.
-    val canvas = document.getElementById("ComposeTarget") as HTMLCanvasElement
+    val canvas = document.getElementById(canvasId) as HTMLCanvasElement
 
     init {
         layer.layer.attachTo(canvas)
         canvas.setAttribute("tabindex", "0")
+        layer.layer.needRedraw()
+
+        layer.setSize(canvas.width, canvas.height)
+    }
 
+    fun resize(newSize: IntSize) {
+        canvas.width = newSize.width
+        canvas.height = newSize.height
+        layer.layer.attachTo(canvas)
         layer.setSize(canvas.width, canvas.height)
+        layer.layer.needRedraw()
     }
 
     /**
@@ -82,3 +99,64 @@ internal actual class ComposeWindow actual constructor() {
         layer.dispose()
     }
 }
+
+private val defaultCanvasElementId = "ComposeTarget"
+
+@ExperimentalComposeUiApi
+/**
+ * EXPERIMENTAL! Might be deleted or changed in the future!
+ *
+ * Initializes the composition in HTML canvas identified by [canvasElementId].
+ *
+ * It can be resized by providing [requestResize].
+ * By default, it will listen to the window resize events.
+ */
+fun CanvasBasedWindow(
+    title: String = "JetpackNativeWindow",
+    canvasElementId: String = defaultCanvasElementId,
+    requestResize: (suspend () -> IntSize)? = null,
+    content: @Composable () -> Unit = { }
+) {
+
+    val actualRequestResize: suspend () -> IntSize = if (requestResize != null) {
+        requestResize
+    } else {
+        // we use Channel instead of suspendCancellableCoroutine,
+        // because we want to drop old resize events
+        val channel = Channel<IntSize>(capacity = CONFLATED)
+
+        // we subscribe to 'resize' only once and never unsubscribe,
+        // because the default behaviour expects that the Canvas takes the entire window space,
+        // so the app has the same lifecycle as the browser tab.
+        window.addEventListener("resize", { _ ->
+            val w = document.documentElement?.clientWidth ?: 0
+            val h = document.documentElement?.clientHeight ?: 0
+            channel.trySend(IntSize(w, h))
+        })
+
+        suspend {
+            channel.receive()
+        }
+    }
+
+    if (requestResize == null) {
+        (document.getElementById(canvasElementId) as? HTMLCanvasElement)?.let {
+            it.width = document.documentElement?.clientWidth ?: 0
+            it.height = document.documentElement?.clientHeight ?: 0
+        }
+    }
+
+    ComposeWindow(canvasId = canvasElementId).apply {
+        val composeWindow = this
+        setContent {
+            content()
+            LaunchedEffect(Unit) {
+                while (isActive) {
+                    val newSize = actualRequestResize()
+                    composeWindow.resize(newSize)
+                    delay(100) // throttle
+                }
+            }
+        }
+    }
+}