Canvas stops displaying after a few seconds.

[Tom Schindl]

You need to interface with the Canvas on the JavaFX-Thread, or even
better don't use a Thread use Timeline with a KeyFrame.

Tom

On 16.03.16 23:25, ZHANG Erkang wrote:
> Hello everyone,
> 
> 
> I'm trying to display a million ovals in a canvas dynamicly every second. I use a thread as the rendering thread, but my problem is, after a few secondes, the canvas freezes and stops displaying. I guess that the buffer is full so it can't display anymore, but how can I clear up the buffer? The test source code is as follow:
> 
> 
> public class Main extends Application {
> 
>     public void start(Stage primaryStage) {
>         primaryStage.setTitle("Drawing Operations Test");
>         Group root = new Group();
>         Canvas canvas = new Canvas(800, 800);
>         GraphicsContext gc = canvas.getGraphicsContext2D();
>         drawShapes(gc);
>         root.getChildren().add(canvas);
>         primaryStage.setScene(new Scene(root));
>         primaryStage.show();
>         Task task2 = new Task<Void>()
>         {
>             public synchronized Void call() throws Exception {
>                 while (true) {
>                     Thread.sleep(1000);
>                     Canvas canvas = gc.getCanvas();
>                     canvas.getGraphicsContext2D().clearRect(0, 0, canvas.getHeight(), canvas.getWidth());
>                     drawShapes(canvas.getGraphicsContext2D());
> 
>                 }
>             }
>         };
>         Thread t = new Thread(task2);
>         t.start();
>     }
> 
>     private void drawShapes(GraphicsContext gc) {
>         gc.setFill(Color.GREEN);
>         gc.setStroke(Color.BLUE);
>         gc.setLineWidth(1);
>         double widthOval=1;
>         double heightOval = 1;
>         for (int i = 0; i < 500; ++i) {
>             for (int j = 0; j < 500; ++j) {
> 
>                 if (Math.random() < 0.5) {
>                     gc.fillOval(i * widthOval, j * heightOval, widthOval, heightOval);
>                 }
>                 else {
>                     gc.strokeOval(i * widthOval, j * heightOval, widthOval, heightOval);
>                 }
>             }
>         }
>     }
> 
>     public static void main(String[] args) {
>         launch(args);
>     }
> }
> 
> 
> 
> Can anyone help me?
> 
> Thanks in advance,
> 
> Pierre
> 


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Thomas Schindl, CTO
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