Avoid calling SkiaLayer.revalidate() when the window itself is moved. (#1010)

Author: m-sasha

skiko/src/awtMain/kotlin/org/jetbrains/skiko/SkiaLayer.awt.kt

@@ -8,6 +8,7 @@ import org.jetbrains.skiko.redrawer.Redrawer
 import org.jetbrains.skiko.redrawer.RedrawerManager
 import java.awt.Color
 import java.awt.Component
+import java.awt.Point
 import java.awt.event.*
 import java.awt.geom.AffineTransform
 import java.awt.im.InputMethodRequests
@@ -20,7 +21,6 @@ import javax.swing.SwingUtilities.isEventDispatchThread
 import javax.swing.UIManager
 import javax.swing.event.AncestorEvent
 import javax.swing.event.AncestorListener
-import kotlin.math.ceil
 import kotlin.math.floor
 
 actual open class SkiaLayer internal constructor(
@@ -138,12 +138,34 @@ actual open class SkiaLayer internal constructor(
         add(backedLayer)
 
         addAncestorListener(object : AncestorListener {
-            override fun ancestorAdded(event: AncestorEvent?) = Unit
 
-            override fun ancestorRemoved(event: AncestorEvent?) = Unit
+            private var positionInWindow: Point? = null
+
+            private val zeroPoint = Point(0, 0)
+
+            private fun computePositionInWindow(): Point? {
+                val window = SwingUtilities.getWindowAncestor(this@SkiaLayer)
+                return if (window == null) {
+                    null
+                } else {
+                    SwingUtilities.convertPoint(this@SkiaLayer, zeroPoint, window)
+                }
+            }
+
+            override fun ancestorAdded(event: AncestorEvent?) {
+                positionInWindow = computePositionInWindow()
+            }
+
+            override fun ancestorRemoved(event: AncestorEvent?) {
+                positionInWindow = null
+            }
 
             override fun ancestorMoved(event: AncestorEvent?) {
-                revalidate()
+                val newPosition = computePositionInWindow()
+                if ((positionInWindow != null) && (positionInWindow != newPosition)) {
+                    revalidate()
+                }
+                positionInWindow = newPosition
             }
         })
 
@@ -190,7 +212,6 @@ actual open class SkiaLayer internal constructor(
         init(isInited)
     }
 
-
     actual fun detach() {
         dispose()
     }

skiko/src/awtTest/kotlin/org/jetbrains/skiko/SkiaLayerTest.kt

@@ -1,13 +1,9 @@
 package org.jetbrains.skiko
 
-import kotlinx.coroutines.CompletableDeferred
-import kotlinx.coroutines.delay
-import kotlinx.coroutines.launch
-import kotlinx.coroutines.yield
+import kotlinx.coroutines.*
+import org.jetbrains.skia.*
 import org.jetbrains.skia.Canvas
-import org.jetbrains.skia.FontMgr
 import org.jetbrains.skia.Paint
-import org.jetbrains.skia.Rect
 import org.jetbrains.skia.paragraph.FontCollection
 import org.jetbrains.skia.paragraph.ParagraphBuilder
 import org.jetbrains.skia.paragraph.ParagraphStyle
@@ -24,9 +20,8 @@ import org.junit.Assume.assumeTrue
 import org.junit.Ignore
 import org.junit.Rule
 import org.junit.Test
-import java.awt.BorderLayout
+import java.awt.*
 import java.awt.Color
-import java.awt.Dimension
 import java.awt.event.*
 import javax.swing.Box
 import javax.swing.JFrame
@@ -941,6 +936,37 @@ class SkiaLayerTest {
         }
     }
 
+    @Test
+    fun `content not relaid out on window move`() = uiTest {
+        var layoutCount = 0
+
+        val window = UiTestWindow {
+            contentPane.layout = object: BorderLayout() {
+                override fun layoutContainer(parent: Container?) {
+                    super.layoutContainer(parent)
+                    layoutCount++
+                }
+            }
+            contentPane.add(layer)
+        }
+        window.size = Dimension(400, 400)
+        window.isVisible = true
+
+        repeat(20) {
+            window.location = window.location.let {
+                java.awt.Point(it.x + 10, it.y + 10)
+            }
+            delay(50)
+        }
+
+        // Ideally, layoutCount would be just 1, but Swing appears to call layout one extra time, so it ends up being 2.
+        // Compare to 3 just to avoid a false-failure if there's another layout for whatever reason.
+        // What we're interested to validate is that there's no layout occurring on every window move.
+        assert(layoutCount <= 3) {
+            "Layout count: $layoutCount"
+        }
+    }
+
     private class RectRenderer(
         private val layer: SkiaLayer,
         var rectWidth: Int,