Fitting rotated ImageView into Application Window / Scene - javafx

Question

In JavaFX I am trying to show an rotated ImageView in an Application Window.
Therefore I have put it into a stackPane to have it always centered and I have bound the widths/heights of the ImageView and the stackPane to the scene's width/height to view it just as large as possible.
This works fine as soon as the Image is not rotated.
As soon as I rotate the Image by 90° using stackPane.setRotate(90) (and exchange binding for width/height) then the stackPane is no longer bound to the upper left corner of the Application Window (or scene).
What can I do to place the rotated image correctly?
In the example code [any key] will toggle the rotation 90°/0° so the location problem of the rotated image becomes visible:
public class RotationTest extends Application {
boolean rotated = false;
public static void main(String[] args) {
Application.launch(args);
}
#Override
public void start(Stage primaryStage) {
primaryStage.setTitle("Rotation test");
Group root = new Group();
Scene scene = new Scene(root, 1024,768);
//a stackPane is used to center the image
StackPane stackPane = new StackPane();
stackPane.setStyle("-fx-background-color: black;");
stackPane.prefHeightProperty().bind(scene.heightProperty());
stackPane.prefWidthProperty().bind(scene.widthProperty());
scene.setOnKeyPressed(new EventHandler<KeyEvent>() {
#Override
public void handle(KeyEvent event) {
//toggle rotate 90° / no rotation
rotated = !rotated;
stackPane.prefHeightProperty().unbind();
stackPane.prefWidthProperty().unbind();
if (rotated){
stackPane.setRotate(90);
//rotation: exchange width and height for binding to scene
stackPane.prefWidthProperty().bind(scene.heightProperty());
stackPane.prefHeightProperty().bind(scene.widthProperty());
}else{
stackPane.setRotate(0);
//no rotation: height is height and width is width
stackPane.prefHeightProperty().bind(scene.heightProperty());
stackPane.prefWidthProperty().bind(scene.widthProperty());
}
}
});
final ImageView imageView = new ImageView("file:D:/test.jpg");
imageView.setPreserveRatio(true);
imageView.fitWidthProperty().bind(stackPane.prefWidthProperty());
imageView.fitHeightProperty().bind(stackPane.prefHeightProperty());
stackPane.getChildren().add(imageView);
root.getChildren().add(stackPane);
primaryStage.setScene(scene);
primaryStage.show();
}
}
Results:
Without rotation the stackPane (black) fits the window perfectly and the image has the correct size even if the window is resized with the mouse.
After pressing [any key] the stackPane is rotated. The stackPane (black) seems to have the correct width/height and also the image seems to be correctly rotated. But the stackPane is no longer in the upper left corner??? It moves around when the window is resized with the mouse???

Answer 1

Why not simply leave the Group and the preferred sizes out of the equation?
The root is automatically resized to fit the scene and you can use it's width/height properties to bind the fitWidth and fitHeight properties:
private static void setRotated(boolean rotated, ImageView targetNode, Pane parent) {
double angle;
if (rotated) {
angle = 90;
targetNode.fitWidthProperty().bind(parent.heightProperty());
targetNode.fitHeightProperty().bind(parent.widthProperty());
} else {
angle = 0;
targetNode.fitWidthProperty().bind(parent.widthProperty());
targetNode.fitHeightProperty().bind(parent.heightProperty());
}
targetNode.setRotate(angle);
}
#Override
public void start(Stage primaryStage) {
Image image = new Image("file:D:/test.jpg");
ImageView imageView = new ImageView(image);
imageView.setPreserveRatio(true);
StackPane root = new StackPane(imageView);
root.setStyle("-fx-background-color: black;");
// initialize unrotated
setRotated(false, imageView, root);
Scene scene = new Scene(root, 1024, 768);
scene.setOnKeyPressed(evt -> {
// toggle between 0° and 90° rotation
setRotated(imageView.getRotate() == 0, imageView, root);
});
primaryStage.setScene(scene);
primaryStage.show();
}
Note that this may not result in correct layout, if placed in some other layout, since the size constraints may be calculated wrong.
You could implement your own region though to fix this:
public class CenteredImage extends Region {
private final BooleanProperty rotated = new SimpleBooleanProperty();
private final ImageView imageView = new ImageView();
public CenteredImage() {
// make sure layout gets invalidated when the image changes
InvalidationListener listener = o -> requestLayout();
imageProperty().addListener(listener);
rotated.addListener((o, oldValue, newValue) -> {
imageView.setRotate(newValue ? 90 : 0);
requestLayout();
});
getChildren().add(imageView);
imageView.setPreserveRatio(true);
}
public final BooleanProperty rotatedProperty() {
return rotated;
}
public final void setRotated(boolean value) {
this.rotated.set(value);
}
public boolean isRotated() {
return rotated.get();
}
public final void setImage(Image value) {
imageView.setImage(value);
}
public final Image getImage() {
return imageView.getImage();
}
public final ObjectProperty<Image> imageProperty() {
return imageView.imageProperty();
}
#Override
protected double computeMinWidth(double height) {
return 0;
}
#Override
protected double computeMinHeight(double width) {
return 0;
}
#Override
protected double computePrefWidth(double height) {
Image image = getImage();
Insets insets = getInsets();
double add = 0;
if (image != null && height > 0) {
height -= insets.getBottom() + insets.getTop();
add = isRotated()
? height / image.getWidth() * image.getHeight()
: height / image.getHeight() * image.getWidth();
}
return insets.getLeft() + insets.getRight() + add;
}
#Override
protected double computePrefHeight(double width) {
Image image = getImage();
Insets insets = getInsets();
double add = 0;
if (image != null && width > 0) {
width -= insets.getLeft() + insets.getRight();
add = isRotated()
? width / image.getHeight() * image.getWidth()
: width / image.getWidth() * image.getHeight();
}
return insets.getTop() + insets.getBottom() + add;
}
#Override
protected double computeMaxWidth(double height) {
return Double.MAX_VALUE;
}
#Override
protected double computeMaxHeight(double width) {
return Double.MAX_VALUE;
}
#Override
protected void layoutChildren() {
Insets insets = getInsets();
double left = insets.getLeft();
double top = insets.getTop();
double availableWidth = getWidth() - left - insets.getRight();
double availableHeight = getHeight() - top - insets.getBottom();
// set fit sizes
if (isRotated()) {
imageView.setFitWidth(availableHeight);
imageView.setFitHeight(availableWidth);
} else {
imageView.setFitWidth(availableWidth);
imageView.setFitHeight(availableHeight);
}
// place image
layoutInArea(imageView, left, top, availableWidth, availableHeight, 0, null, false,
false, HPos.CENTER, VPos.CENTER);
}
}
#Override
public void start(Stage primaryStage) {
Image image = new Image("file:D:/test.jpg");
ImageView imageView = new ImageView(image);
imageView.setPreserveRatio(true);
CenteredImage imageArea = new CenteredImage();
imageArea.setImage(image);
imageArea.setStyle("-fx-background-color: black;");
imageArea.setPrefWidth(300);
SplitPane splitPane = new SplitPane(new Region(), imageArea);
SplitPane.setResizableWithParent(imageArea, true);
Scene scene = new Scene(splitPane, 1024, 768);
scene.setOnKeyPressed(evt -> {
// toggle between 0° and 90° rotation
imageArea.setRotated(!imageArea.isRotated());
});
primaryStage.setScene(scene);
primaryStage.show();
}

Answer 2

I found a solution :-) Fabian's approach inspired me (thank you!!) And my old friend Pit helped me with debugging (also thank you!!)
It seems that the layout location algorithm of JavaFX has a problem when resize() is applied to rotated Panes (or even Nodes - I have not tried):
Following Fabian's idea I debugged into the layoutChildren() method of class Pane. I found that the relocation after setRotate() is correct and keeps the center of the child pane as expected. But as soon as resize() is called (which is done because of fitting the rotated child pane again into its father and additionally always when the window is resized by the user) the origin calculation goes wrong:
The picture above depicts a sequence of setRotate(90), resize() and relocate() in green and the same for setRotate(270) in blue. A little blue/green circle depicts the corresponding origin together with its coordinates in the 1024x786 example.
Analysis
It seems that for calculation the position of the Pane resize() does not use the height and width from BoundsInParent-Property (see JavaFX-Docu of Node) but from getWidth() and getHeight() which seem to reflect BoundsInLocal. As a consequence, for rotations of 90° or 270° height and width seem to be interchanged. Therefore the error in the calculation for the new origin is just the half of the difference between width and height (delta=(width-height)/2) when resize() tries to center the child pane again after the resizing.
Solution
A relocation(delta,-delta) needs to be applied after resizing for Panes with rotation=90 or 270 degrees.
The structure of my implementation follows Fabian's basic idea: I have build a layouter RotatablePaneLayouter:Region that just overwrites the layoutChildren() method. In its constructor it gets a Pane (in my example a StackPane) which can contain any number of children (in my example an ImageView) and that can be rotated.
LayoutChildren() then just executes resize() and relocate() for the child pane to fit it completely into the RotateablePaneLayouter respecting the orientation of the child pane.
The Layouter Helper (RotateablePaneLayouter:Region)
public class RotatablePaneLayouter extends Region {
private Pane child;
public RotatablePaneLayouter(Pane child) {
getChildren().add(child);
this.child = child;
// make sure layout gets invalidated when the child orientation changes
child.rotateProperty().addListener(new ChangeListener<Number>() {
#Override
public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
requestLayout();
}
});
}
#Override
protected void layoutChildren() {
// set fit sizes:
//resize child to fit into RotatablePane and correct movement caused by resizing if necessary
if ((child.getRotate() == 90)||(child.getRotate() == 270)) {
//vertical
child.resize( getHeight(), getWidth() ); //exchange width and height
// and relocate to correct movement caused by resizing
double delta = (getWidth() - getHeight()) / 2;
child.relocate(delta,-delta);
} else {
//horizontal
child.resize( getWidth(), getHeight() ); //keep width and height
//with 0° or 180° resize does no movement to be corrected
child.relocate(0,0);
}
}
}
To use it: Place the Pane to be rotated into the Layouter first instead of placing the Pane directly.
Here the code for the example's main program. You can use the space bar to rotate the child pane by 90, 180, 270 and again 0 degrees. You can also resize the window with the mouse. The layouter always manages to place the rotated pane correctly.
Expample for using the Layouter
public class RotationTest extends Application {
public static void main(String[] args) {
Application.launch(args);
}
#Override
public void start(Stage primaryStage) {
//image in a StackPane to be rotated
final ImageView imageView = new ImageView("file:D:/Test_org.jpg");
imageView.setPreserveRatio(true);
StackPane stackPane = new StackPane(imageView); //a stackPane is used to center the image
stackPane.setStyle("-fx-background-color: black;");
imageView.fitWidthProperty().bind(stackPane.widthProperty());
imageView.fitHeightProperty().bind(stackPane.heightProperty());
//container for layouting rotated Panes
RotatablePaneLayouter root = new RotatablePaneLayouter(stackPane);
root.setStyle("-fx-background-color: blue;");
Scene scene = new Scene(root, 1024,768);
scene.setOnKeyPressed(new EventHandler<KeyEvent>() {
#Override
public void handle(KeyEvent event) {
if (event.getCode() == KeyCode.SPACE) {
//rotate additionally 90°
stackPane.setRotate((stackPane.getRotate() + 90) % 360);
}
}
});
primaryStage.setTitle("Rotation test");
primaryStage.setScene(scene);
primaryStage.show();
}
}
For me this seems like a workaround of a javaFX bug in resize().