Feature: 3D Renderer and Preview Export of Thumbnails

vitrivr-engine-module-m3d/src/main/kotlin/org/vitrivr/engine/model3d/renderer/ExternalRenderer.kt

@@ -6,6 +6,7 @@ import org.vitrivr.engine.model3d.data.render.lwjgl.render.RenderOptions
 import org.vitrivr.engine.model3d.data.render.lwjgl.window.WindowOptions
 import java.awt.image.BufferedImage
 import java.io.Closeable
+import java.io.IOException
 import java.io.ObjectInputStream
 import java.io.ObjectOutputStream
 
@@ -17,27 +18,11 @@ import java.io.ObjectOutputStream
  */
 class ExternalRenderer : Closeable {
 
-    private val process: Process
+    private var process: RenderProcess? = null
 
-    /** The [ObjectOutputStream] used by the [ExternalRenderer]. */
-    private val oos: ObjectOutputStream
-
-    /** The [ObjectInputStream] used by the [ExternalRenderer]. */
-    private val ois: ObjectInputStream
-
-    init {
-        val javaHome = System.getProperty("java.home")
-        val javaBin = "$javaHome/bin/java"
-        val classpath = System.getProperty("java.class.path")
-        val className = "org.vitrivr.engine.model3d.renderer.RendererKt"
-
-        val processBuilder = ProcessBuilder(javaBin, "-cp", classpath, "-XstartOnFirstThread", className)
-        this.process = processBuilder.start()
-
-        /* Initialize streams. */
-        this.oos = ObjectOutputStream(this.process.outputStream)
-        this.ois = ObjectInputStream(this.process.inputStream)
-    }
+    @Volatile
+    /** Flag indicating whether the [ExternalRenderer] is closed. */
+    private var closed: Boolean = false
 
     /**
      * Renders the given [Model3d] using the [ExternalRenderer].
@@ -47,21 +32,101 @@ class ExternalRenderer : Closeable {
      * @param windowOptions The [WindowOptions] to use for rendering.
      * @param renderOptions The [RenderOptions] to use for rendering.
      */
+    @Synchronized
     fun render(model: Model3d, cameraPositions: List<Vector3f>, windowOptions: WindowOptions, renderOptions: RenderOptions): List<BufferedImage> {
-        /* Create request and write it to stream. */
+        check(!this.closed) { "ExternalRenderer is closed and cannot be used for processing." }
+        var process = this.process
+        if (process == null || !process.isAlive()) {
+            process?.close()
+            process = RenderProcess()
+            this.process = process
+        }
+
+        /* Send request. */
         val request = RenderRequest(model, cameraPositions, windowOptions, renderOptions)
-        this.oos.writeObject(request)
-        this.oos.flush()
+        val response = process.send(request)
 
-        /* Read request. */
-        val image = this.ois.readObject() as? RenderResponse ?: throw IllegalStateException("Could not parse model.")
-        return image.images()
+        /* Return images . */
+        return response.images()
     }
 
     /**
      * Closes the [ExternalRenderer] and the associated process.
      */
     override fun close() {
-        this.process.destroy()
+        if (!this.closed) {
+            this.closed = true
+            this.process?.close()
+            this.process = null
+        }
+    }
+
+    /**
+     * A [RenderProcess] is a helper class that wraps the [Process] used by the [ExternalRenderer].
+     */
+    private inner class RenderProcess: Closeable {
+
+        /** The [Process] used by the [ExternalRenderer]. */
+        val process: Process
+
+        /** The [ObjectOutputStream] used by the [ExternalRenderer]. */
+        val oos: ObjectOutputStream
+
+        /** The [ObjectInputStream] used by the [ExternalRenderer]. */
+        val ois: ObjectInputStream
+
+        init {
+            val javaHome = System.getProperty("java.home")
+            val javaBin = "$javaHome/bin/java"
+            val classpath = System.getProperty("java.class.path")
+            val className = "org.vitrivr.engine.model3d.renderer.RendererKt"
+
+            val processBuilder = ProcessBuilder(javaBin, "-cp", classpath, "-XstartOnFirstThread", className)
+            this.process = processBuilder.start()
+
+            /* Initialize streams. */
+            this.oos = ObjectOutputStream(this.process.outputStream)
+            this.ois = ObjectInputStream(this.process.inputStream)
+        }
+
+        /**
+         * Sends a [RenderRequest] to the external renderer.
+         */
+        fun send(request: RenderRequest): RenderResponse {
+            /* Write request to output stream. */
+            try {
+                this.oos.writeObject(request)
+                this.oos.flush()
+            } catch (e: IOException) {
+                this.oos.reset()
+                throw IllegalStateException("Could not send request due to IO exception.", e)
+            }
+
+            /* Read response and return image. */
+            val image = try {
+                this.ois.readObject() as? RenderResponse ?: throw IllegalStateException("Could not parse model.")
+            } catch (e: IOException) {
+                this.ois.reset()
+                throw IllegalStateException("Could not parse model due to IO exception.", e)
+            }
+            return image
+        }
+
+        /**
+         * Checks if the process is still alive.
+         */
+        fun isAlive(): Boolean {
+            return this.process.isAlive
+        }
+
+        /**
+         * Checks if the process is still alive.
+         */
+        override fun close() = try {
+            this.oos.close()
+            this.ois.close()
+        } finally {
+            this.process.destroy()
+        }
     }
 }