Fix rendering of an empty layer on metal (#504)

* Fix rendering of an empty layer on metal

* Fix Windows

skiko/src/awtMain/kotlin/org/jetbrains/skiko/context/DirectSoftwareContextHandler.kt

@@ -38,17 +38,25 @@ internal class DirectSoftwareContextHandler(layer: SkiaLayer) : JvmContextHandle
         val h = (layer.height * scale).toInt().coerceAtLeast(0)
         if (isSizeChanged(w, h) || surface == null) {
             disposeCanvas()
+            if (w > 0 && h > 0) {
                 softwareRedrawer.resize(w, h)
                 surface = softwareRedrawer.acquireSurface()
                 canvas = surface!!.canvas
+            } else {
+                surface = null
+                canvas = null
+            }
         }
     }
 
     override fun flush() {
+        val surface = surface
+        if (surface != null) {
             try {
-            softwareRedrawer.finishFrame(getPtr(surface!!))
+                softwareRedrawer.finishFrame(getPtr(surface))
             } finally {
-            Reference.reachabilityFence(surface!!)
+                Reference.reachabilityFence(surface)
+            }
         }
     }
 }
\ No newline at end of file

skiko/src/awtMain/kotlin/org/jetbrains/skiko/context/MetalContextHandler.kt

@@ -34,6 +34,7 @@ internal class MetalContextHandler(layer: SkiaLayer) : JvmContextHandler(layer)
         val w = (layer.width * scale).toInt().coerceAtLeast(0)
         val h = (layer.height * scale).toInt().coerceAtLeast(0)
 
+        if (w > 0 && h > 0) {
             renderTarget = metalRedrawer.makeRenderTarget(w, h)
 
             surface = Surface.makeFromBackendRenderTarget(
@@ -45,11 +46,16 @@ internal class MetalContextHandler(layer: SkiaLayer) : JvmContextHandler(layer)
             ) ?: throw RenderException("Cannot create surface")
 
             canvas = surface!!.canvas
+        } else {
+            renderTarget = null
+            surface = null
+            canvas = null
+        }
     }
 
     override fun flush() {
         super.flush()
-        surface!!.flushAndSubmit()
+        surface?.flushAndSubmit()
         metalRedrawer.finishFrame()
     }
 

skiko/src/iosMain/kotlin/org/jetbrains/skiko/context/MetalContextHandler.kt

@@ -47,6 +47,7 @@ internal class MetalContextHandler(layer: SkiaLayer) : ContextHandler(layer, lay
             metalRedrawer.syncSize()
         }
 
+        if (w > 0 && h > 0) {
             renderTarget = metalRedrawer.makeRenderTarget(w, h)
 
             surface = Surface.makeFromBackendRenderTarget(
@@ -58,12 +59,17 @@ internal class MetalContextHandler(layer: SkiaLayer) : ContextHandler(layer, lay
             ) ?: throw RenderException("Cannot create surface")
 
             canvas = surface!!.canvas
+        } else {
+            renderTarget = null
+            surface = null
+            canvas = null
+        }
     }
 
     override fun flush() {
         // TODO: maybe make flush async as in JVM version.
         super.flush()
-        surface!!.flushAndSubmit()
+        surface?.flushAndSubmit()
         metalRedrawer.finishFrame()
     }
 

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

@@ -25,6 +25,7 @@ import java.awt.Color
 import java.awt.Dimension
 import java.awt.event.WindowEvent
 import javax.swing.JFrame
+import javax.swing.JLayeredPane
 import javax.swing.WindowConstants
 import kotlin.random.Random
 import kotlin.test.assertTrue
@@ -135,6 +136,55 @@ class SkiaLayerTest {
         }
     }
 
+    @Test
+    fun `render empty layer`() = uiTest {
+        val window = JFrame()
+        val layer = SkiaLayer(
+            properties = SkiaLayerProperties(renderApi = renderApi)
+        )
+        var renderedWidth = -1
+        layer.skikoView = object : SkikoView {
+            override fun onRender(canvas: Canvas, width: Int, height: Int, nanoTime: Long) {
+                renderedWidth = width
+            }
+        }
+        layer.size = Dimension(0, 0)
+        val density = window.graphicsConfiguration.defaultTransform.scaleX
+        try {
+            val panel = JLayeredPane()
+            panel.add(layer)
+            window.contentPane.add(panel)
+            window.setLocation(200, 200)
+            window.size = Dimension(200, 200)
+            window.defaultCloseOperation = WindowConstants.DISPOSE_ON_CLOSE
+            window.isUndecorated = true
+            window.isVisible = true
+            layer.needRedraw()
+            delay(1000)
+            assertEquals(0, renderedWidth)
+
+            renderedWidth = -1
+            layer.needRedraw()
+            delay(1000)
+            assertEquals(0, renderedWidth)
+
+            renderedWidth = -1
+            layer.size = Dimension(30, 40)
+            layer.needRedraw()
+            delay(1000)
+            assertEquals((30 * density).toInt(), renderedWidth)
+
+            renderedWidth = -1
+            layer.size = Dimension(0, 0)
+            layer.needRedraw()
+            delay(1000)
+            assertEquals(0, renderedWidth)
+        } finally {
+            layer.dispose()
+            window.close()
+        }
+    }
+
     @Test
     fun `resize window`() = uiTest {
         val window = UiTestWindow()

skiko/src/macosMain/kotlin/org/jetbrains/skiko/context/MetalContextHandler.macos.kt

@@ -35,6 +35,7 @@ internal class MacOsMetalContextHandler(layer: SkiaLayer) : ContextHandler(layer
         val w = (layer.nsView.frame.useContents { size.width } * scale).toInt().coerceAtLeast(0)
         val h = (layer.nsView.frame.useContents { size.height } * scale).toInt().coerceAtLeast(0)
 
+        if (w > 0 && h > 0) {
             renderTarget = metalRedrawer.makeRenderTarget(w, h)
 
             surface = Surface.makeFromBackendRenderTarget(
@@ -46,12 +47,17 @@ internal class MacOsMetalContextHandler(layer: SkiaLayer) : ContextHandler(layer
             ) ?: throw RenderException("Cannot create surface")
 
             canvas = surface!!.canvas
+        } else {
+            renderTarget = null
+            surface = null
+            canvas = null
+        }
     }
 
     override fun flush() {
         // TODO: maybe make flush async as in JVM version.
         super.flush()
-        surface!!.flushAndSubmit()
+        surface?.flushAndSubmit()
         metalRedrawer.finishFrame()
     }