Fixes ImageConverter running in the wrong thread

If an image changed dimention in the preview pane
it's UI counterpart could be changed in the wrong thread.
This could cause random ArrayOutOfBounds Exceptions without
any context as to what was causing the problem.
This forces the ImageConverter.convert method to be run in the
UI thread or it will throw an exception.

Possibly related: #225

Author: JLLeitschuh

ui/src/main/java/edu/wpi/grip/ui/preview/BlobsSocketPreviewView.java

@@ -87,10 +87,10 @@ private void convertImage() {
                 }
             }
 
-            final Image image = this.imageConverter.convert(input);
+            final Mat inputToConvert = input;
             final int numBlobs = blobsReport.getBlobs().size();
-
             platform.runAsSoonAsPossible(() -> {
+                final Image image = this.imageConverter.convert(inputToConvert);
                 this.imageView.setImage(image);
                 this.infoLabel.setText("Found " + numBlobs + " blobs");
             });

ui/src/main/java/edu/wpi/grip/ui/preview/ContoursSocketPreviewView.java

@@ -84,9 +84,10 @@ private void render() {
                 }
             }
 
-            final Image image = this.imageConverter.convert(tmp);
             final long finalNumContours = numContours;
+            final Mat convertInput = tmp;
             platform.runAsSoonAsPossible(() -> {
+                final Image image = this.imageConverter.convert(convertInput);
                 this.imageView.setImage(image);
                 this.infoLabel.setText("Found " + finalNumContours + " contours");
             });

ui/src/main/java/edu/wpi/grip/ui/preview/ImageSocketPreviewView.java

@@ -44,8 +44,8 @@ public void onSocketChanged(SocketChangedEvent event) {
     private void convertImage() {
         synchronized (this) {
             this.getSocket().getValue().ifPresent(mat -> {
-                final Image image = this.imageConverter.convert(mat);
                 platform.runAsSoonAsPossible(() -> {
+                    final Image image = this.imageConverter.convert(mat);
                     this.imageView.setImage(image);
                 });
 

ui/src/main/java/edu/wpi/grip/ui/preview/LinesSocketPreviewView.java

@@ -94,11 +94,10 @@ private void convertImage() {
                     circle(input, endPoint, 2, Scalar.WHITE, 2, LINE_8, 0);
                 }
             }
-
-            final Image image = this.imageConverter.convert(input);
+            final Mat convertInput = input;
             final int numLines = lines.size();
-
             platform.runAsSoonAsPossible(() -> {
+                final Image image = this.imageConverter.convert(convertInput);
                 this.imageView.setImage(image);
                 this.infoLabel.setText("Found " + numLines + " lines");
             });

ui/src/main/java/edu/wpi/grip/ui/util/ImageConverter.java

@@ -1,6 +1,7 @@
 package edu.wpi.grip.ui.util;
 
 import com.google.common.primitives.UnsignedBytes;
+import javafx.application.Platform;
 import javafx.scene.image.Image;
 import javafx.scene.image.PixelFormat;
 import javafx.scene.image.WritableImage;
@@ -31,6 +32,16 @@ public final class ImageConverter {
      * @return A JavaFX image, or null for empty
      */
     public Image convert(Mat mat) {
+        /*
+         * IMPORTANT!
+         * The {@link ImageConverter#image} is a component that may be actively part of the UI
+         * If we are changing it while it is being rendered by the UI thread this could cause
+         * a problem in the UI thread.
+         */
+        if(!Platform.isFxApplicationThread()) {
+            throw new IllegalStateException("This modifies an FX object. This must be run in the UI Thread");
+        }
+
         final int width = mat.cols();
         final int height = mat.rows();
         final int channels = mat.channels();

ui/src/test/java/edu/wpi/grip/ui/util/ImageConverterTest.java

@@ -3,10 +3,13 @@
 import edu.wpi.grip.core.util.ImageLoadingUtility;
 import edu.wpi.grip.util.Files;
 import edu.wpi.grip.util.ImageWithData;
+import javafx.scene.Scene;
 import javafx.scene.image.Image;
+import javafx.scene.layout.Pane;
+import javafx.stage.Stage;
 import org.bytedeco.javacpp.opencv_core.Mat;
-import org.junit.Before;
 import org.junit.Test;
+import org.testfx.framework.junit.ApplicationTest;
 
 import java.net.URLDecoder;
 import java.nio.file.Paths;
@@ -16,24 +19,34 @@
 import static org.junit.Assert.assertEquals;
 
 
-public class ImageConverterTest {
+public class ImageConverterTest extends ApplicationTest {
     private static final ImageWithData
             gompeiImage = Files.gompeiJpegFile,
             imageFile = Files.imageFile;
 
     private ImageConverter converter;
 
-    @Before
-    public void setUp() {
+    @Override
+    public void start(Stage stage) {
         converter = new ImageConverter();
+        stage.setScene(new Scene(new Pane()));
+        stage.show();
     }
 
     @Test
     public void testConvertImage() throws Exception {
         Mat mat = new Mat();
         ImageLoadingUtility.loadImage(URLDecoder.decode(Paths.get(gompeiImage.file.toURI()).toString()), mat);
-        Image javaFXImage = converter.convert(mat);
-        assertSameImage(gompeiImage, javaFXImage);
+        interact(() -> {
+            Image javaFXImage = converter.convert(mat);
+            assertSameImage(gompeiImage, javaFXImage);
+        });
+
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void testConvertInWrongThreadThrowsIllegalState() {
+        converter.convert(new Mat());
     }
 
     @Test
@@ -42,9 +55,11 @@ public void testConvertImageSwitch() throws Exception {
         Mat imageMat = new Mat();
         ImageLoadingUtility.loadImage(URLDecoder.decode(Paths.get(gompeiImage.file.toURI()).toString()), gompeiMat);
         ImageLoadingUtility.loadImage(URLDecoder.decode(Paths.get(imageFile.file.toURI()).toString()), imageMat);
-        converter.convert(gompeiMat);
-        Image javaFXImage = converter.convert(imageMat);
-        assertSameImage(imageFile, javaFXImage);
+        interact(() -> {
+            converter.convert(gompeiMat);
+            Image javaFXImage = converter.convert(imageMat);
+            assertSameImage(imageFile, javaFXImage);
+        });
     }
 
     @Test
@@ -54,8 +69,10 @@ public void testConvertSingleChanelImage() throws Exception {
         final Mat desaturatedMat = new Mat();
         cvtColor(gompeiMat, desaturatedMat, COLOR_BGR2GRAY);
 
-        Image javaFXImage = converter.convert(desaturatedMat);
-        assertSameImage(gompeiImage, javaFXImage);
+        interact(() -> {
+            Image javaFXImage = converter.convert(desaturatedMat);
+            assertSameImage(gompeiImage, javaFXImage);
+        });
     }
 
     private void assertSameImage(ImageWithData imageWithData, Image javaFXImage) {