JavaFX8 presentation view (duplicate pane and content) - javafx

Question

I'm trying to create a presentation view for my Drawing app, where only the drawing board (pane) is visible. So the user can show the presentation view on the projector while having the actual drawing pane and tools on the PC.
My current approach is to create a Snapshot from the pane in each frame and display it in an ImageView on the second stage.
public void startStream(){
new AnimationTimer() {
#Override
public void handle(long now) {
WritableImage image = drawingPane.snapshot(new SnapshotParameters(), null);
stream.setImage(image);
}
}.start();
final Screen screen = Screen.getPrimary();
final Stage stage = new Stage();
StackPane root = new StackPane();
root.getChildren().add(stream);
Scene scene = new Scene(root, drawingPane.getWidth(), drawingPane.getHeight());
stage.setScene(scene);
stage.setTitle("streaming stage");
Rectangle2D bounds = screen.getBounds();
System.out.println(bounds);
stage.setX(bounds.getMinX() + (bounds.getWidth() - 300) / 2);
stage.setY(bounds.getMinY() + (bounds.getHeight() - 200) / 2);
stage.show();
}
problem here is it's eating a lot of RAM, like 800MB and also 30% more CPU usage. I can understand, that creating an Image on every frame is not efficient, that's why I'd like to ask, if there is a way to get this working more efficiently.
Also if there is a better approach/solution to this feature, I'd be thankful for it.

Answer 1

To reduce the CPU usage, do not make a snapshot in an AnimationTimer—this really makes a snapshot at the frame rate (60 FPS) frequency, even if nothing has changed in the drawingPane. Instead, make the snapshot after drawingPane's layout. Adding a listener to drawingPane's needsLayoutProperty should do the trick:
drawingPane.needsLayoutProperty().addListener((obs, wasDirty, isDirty) -> {
if(!isDirty) {
WritableImage image = drawingPane.snapshot(new SnapshotParameters(), null);
stream.setImage(image);
}
});
This should lower the CPU usage when you are not editing the drawingPane.
It may also lower the memory usage, because garbage collector may kick in faster and collect the old snapshots. If not, consider re-using the WritableImage instance, if it already has the correct size:
WritableImage image = null;
drawingPane.needsLayoutProperty().addListener((obs, wasDirty, isDirty) -> {
if(!isDirty) {
if(this.image != null &&
(this.image.getWidth() != drawingPane.getWidth() ||
this.image.getHeight() != drawingPane.getHeight())) {
this.image = null;
}
this.image = drawingPane.snapshot(new SnapshotParameters(), this.image);
stream.setImage(this.image);
}
});
Note that this answer assumes that children of drawingPane are managed children (which is the default), and thus their layout being marked as dirty causes the drawingPane's layout being marked as dirty, so that you can actually observe any changes of the needsLayout property.