Invalidate parent layer every time child layer is invalidated

compose/ui/ui/src/skikoMain/kotlin/androidx/compose/ui/platform/RenderNodeLayer.skiko.kt

@@ -231,8 +231,8 @@ internal class RenderNodeLayer(
         if (!isDestroyed && picture != null) {
             picture?.close()
             picture = null
-            invalidateParentLayer()
         }
+        invalidateParentLayer()
     }
 
     override fun drawLayer(canvas: Canvas) {

compose/ui/ui/src/skikoTest/kotlin/androidx/compose/ui/platform/GraphicLayerBugTest.kt

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2024 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.compose.ui.platform
+
+import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.ExperimentalFoundationApi
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.pager.HorizontalPager
+import androidx.compose.foundation.pager.rememberPagerState
+import androidx.compose.material.Scaffold
+import androidx.compose.material.TextField
+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.assertThat
+import androidx.compose.ui.draw.drawBehind
+import androidx.compose.ui.isEqualTo
+import androidx.compose.ui.test.ExperimentalTestApi
+import androidx.compose.ui.test.runComposeUiTest
+import androidx.compose.ui.unit.dp
+import kotlin.test.Test
+
+// Tests for fixed bugs
+class GraphicLayerBugTest {
+    // https://github.com/JetBrains/compose-multiplatform/issues/4681
+    @OptIn(ExperimentalTestApi::class, ExperimentalFoundationApi::class)
+    @Test
+    fun draw_invalidates_inside_complex_layout() =
+        runComposeUiTest {
+            var valueForDraw by mutableStateOf(0f)
+            var lastDrawnValue = -1f
+
+            setContent {
+                val pagerState = rememberPagerState { 1 }
+                Scaffold(
+                    modifier = Modifier.fillMaxSize(),
+                    topBar = {
+                        Spacer(Modifier.drawBehind { pagerState.targetPage })
+                    },
+                ) {
+                    HorizontalPager(modifier = Modifier.fillMaxSize(), state = pagerState) {
+                        var value by remember { mutableStateOf("") }
+                        TextField(
+                            value = value,
+                            onValueChange = { value = it },
+                        )
+
+                        Canvas(Modifier.size(40.dp)) {
+                            lastDrawnValue = valueForDraw
+                        }
+                    }
+                }
+            }
+
+            waitForIdle()
+            assertThat(lastDrawnValue).isEqualTo(0f)
+
+            valueForDraw = 1f
+            waitForIdle()
+            assertThat(lastDrawnValue).isEqualTo(1f)
+        }
+}

compose/ui/ui/src/skikoTest/kotlin/androidx/compose/ui/platform/RenderNodeLayerTest.kt

@@ -17,15 +17,18 @@
 package androidx.compose.ui.platform
 
 import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.ui.assertThat
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.graphics.*
+import androidx.compose.ui.isEqualTo
 import androidx.compose.ui.unit.*
 import kotlin.math.PI
 import kotlin.math.cos
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFalse
 import kotlin.test.assertTrue
+import org.jetbrains.skia.Surface
 
 class RenderNodeLayerTest {
 
@@ -464,11 +467,56 @@ class RenderNodeLayerTest {
         assertTrue(layer.isInLayer(Offset(50f, 100f)))
     }
 
-    private fun TestRenderNodeLayer() = RenderNodeLayer(
+    @Test
+    fun invalidate_parent_layer() {
+        var parentDrawCount = 0
+
+        var childLayer: RenderNodeLayer? = null
+        val parentLayer = TestRenderNodeLayer(
+            drawBlock = {
+                parentDrawCount++
+                childLayer?.drawLayer(it)
+            },
+        )
+
+        val surface = Surface.makeNull(10, 10)
+        val canvas = surface.canvas.asComposeCanvas()
+
+        assertThat(parentDrawCount).isEqualTo(0)
+
+        parentLayer.drawLayer(canvas)
+        assertThat(parentDrawCount).isEqualTo(1)
+
+        // shouldn't be drawn again, as it isn't changed
+        parentLayer.drawLayer(canvas)
+        assertThat(parentDrawCount).isEqualTo(1)
+
+        // https://github.com/JetBrains/compose-multiplatform/issues/4681
+        // parent should be drawn again, as we add a child
+        childLayer = TestRenderNodeLayer(
+            invalidateParentLayer = parentLayer::invalidate,
+            drawBlock = {},
+        )
+        childLayer.invalidate()
+        parentLayer.drawLayer(canvas)
+        assertThat(parentDrawCount).isEqualTo(2)
+
+        parentLayer.drawLayer(canvas)
+        assertThat(parentDrawCount).isEqualTo(2)
+
+        childLayer.invalidate()
+        parentLayer.drawLayer(canvas)
+        assertThat(parentDrawCount).isEqualTo(3)
+    }
+
+    private fun TestRenderNodeLayer(
+        invalidateParentLayer: () -> Unit = {},
+        drawBlock: (Canvas) -> Unit = {},
+    ) = RenderNodeLayer(
         Density(1f, 1f),
         measureDrawBounds = false,
-        invalidateParentLayer = {},
-        drawBlock = {}
+        invalidateParentLayer = invalidateParentLayer,
+        drawBlock = drawBlock,
     )
 
     private fun assertMapping(from: Offset, to: Offset) {