Fix Desktop PlotPanelRaw not showing plot after an error message

Author: IKupriyanov-HORIS

demo/plot/compose-desktop/src/main/kotlin/demo/plot/median/AppMain.kt

@@ -19,18 +19,20 @@ import androidx.compose.ui.unit.dp
 import androidx.compose.ui.window.Window
 import androidx.compose.ui.window.application
 import demo.plot.median.ui.DemoList
-import org.jetbrains.letsPlot.compose.PlotPanel
-import plotSpec.DensitySpec
-import plotSpec.PerfSpec
-import plotSpec.PlotGridSpec
+import org.jetbrains.letsPlot.Figure
+import org.jetbrains.letsPlot.compose.PlotPanelRaw
+import org.jetbrains.letsPlot.intern.toSpec
+import plotSpec.*
 
 fun main() = application {
     Window(onCloseRequest = ::exitApplication, title = "Demo (Compose Desktop, median)") {
 
         val figures = listOf(
             "Density Plot" to DensitySpec().createFigure(),
             "Plot Grid" to PlotGridSpec().createFigure(),
-            "25k Points" to PerfSpec().createFigure()
+            "25k Points" to PerfSpec().createFigure(),
+            "BackendError" to IllegalArgumentSpec().createFigure(),
+            "FrontendError" to FrontendExceptionSpec().createRawSpec(),
         )
 
         val preserveAspectRatio = remember { mutableStateOf(false) }
@@ -65,8 +67,18 @@ fun main() = application {
                         modifier = Modifier.fillMaxSize()
                             .padding(start = 10.dp, top = 10.dp, end = 10.dp, bottom = 10.dp),
                     ) {
-                        PlotPanel(
-                            figure = figures[figureIndex.value].second,
+                        // Cast to rawSpec to use only the PlotPanelRaw
+                        // Switch between PlotPanel and PlotPanelRaw causes re-creation of the whole panel
+                        // and hides bugs related to the panel re-use, like OK -> ERROR -> OK state transition.
+                        val rawSpec: Map<*, *> = when (val fig = figures[figureIndex.value].second) {
+                            is Figure -> fig.toSpec()
+                            is Map<*, *> -> fig
+                            else -> throw IllegalStateException("Unexpected figure type: ${fig.let { it::class }}")
+                        }
+
+                        @Suppress("UNCHECKED_CAST")
+                        PlotPanelRaw(
+                            rawSpec = rawSpec as MutableMap<String, Any>,
                             preserveAspectRatio = preserveAspectRatio.value,
                             modifier = Modifier.fillMaxSize()
                         ) { computationMessages ->

lets-plot-compose/src/desktopMain/kotlin/org/jetbrains/letsPlot/compose/PlotPanelRaw.kt

@@ -19,6 +19,8 @@ import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.text.TextStyle
 import org.jetbrains.letsPlot.commons.geometry.DoubleVector
 import org.jetbrains.letsPlot.commons.logging.PortableLogging
+import org.jetbrains.letsPlot.compose.desktop.PlotContainer
+import org.jetbrains.letsPlot.compose.desktop.SvgViewPanel
 import org.jetbrains.letsPlot.core.plot.builder.interact.tools.FigureModelHelper
 import org.jetbrains.letsPlot.core.spec.Option.Meta.Kind.GG_TOOLBAR
 import org.jetbrains.letsPlot.core.spec.config.PlotConfig
@@ -27,14 +29,14 @@ import org.jetbrains.letsPlot.core.util.MonolithicCommon.processRawSpecs
 import org.jetbrains.letsPlot.core.util.PlotThemeHelper
 import org.jetbrains.letsPlot.core.util.sizing.SizingPolicy
 import org.jetbrains.letsPlot.skia.builder.MonolithicSkia
-import org.jetbrains.letsPlot.compose.desktop.PlotContainer
-import org.jetbrains.letsPlot.compose.desktop.SvgViewPanel
 
 //import org.jetbrains.letsPlot.compose.util.NaiveLogger
 
 //private val LOG = NaiveLogger("PlotPanel")
 private val LOG = PortableLogging.logger(name = "[PlotPanelRaw]")
 
+private const val logRecompositions = true
+
 @Suppress("FunctionName")
 @Composable
 actual fun PlotPanelRaw(
@@ -45,6 +47,9 @@ actual fun PlotPanelRaw(
     errorModifier: Modifier,
     computationMessagesHandler: (List<String>) -> Unit
 ) {
+    if (logRecompositions) {
+        println("PlotPanelRaw: recomposition")
+    }
 
     // Update density on each recomposition to handle monitor DPI changes (e.g., drag between HIDPI/regular monitor)
     val density = LocalDensity.current.density.toDouble()
@@ -60,11 +65,14 @@ actual fun PlotPanelRaw(
     var panelSize by remember { mutableStateOf(DoubleVector.ZERO) }
     var dispatchComputationMessages by remember { mutableStateOf(true) }
     var specOverrideList by remember { mutableStateOf(emptyList<Map<String, Any>>()) }
-    val plotContainer = remember { PlotContainer() }
     var plotFigureModel by remember { mutableStateOf<PlotFigureModel?>(null) }
 
 
-    var errorMessage: String? by remember { mutableStateOf(null) }
+    var errorMessage: String? by remember(processedPlotSpec) { mutableStateOf(null) }
+
+    // Reset the old plot on error to prevent blinking
+    // We can't reset PlotContainer using updateViewmodel(), so we create a new one.
+    val plotContainer = remember(errorMessage) { PlotContainer() }
 
     // Background
     val finalModifier = if (errorMessage != null) {
@@ -123,6 +131,7 @@ actual fun PlotPanelRaw(
                 LaunchedEffect(panelSize, processedPlotSpec, specOverrideList, preserveAspectRatio) {
 
                     if (PlotConfig.isFailure(processedPlotSpec)) {
+                        plotFigureModel = null
                         errorMessage = PlotConfig.getErrorMessage(processedPlotSpec)
                         return@LaunchedEffect
                     }