How to Automatically Resize a JavaFX Canvas Within an Enclosing Container?

How to Resize a Canvas Automatically Within an Enclosing Container

When working with JavaFX's Canvas API and AnimationTimer for animated backgrounds, the task of automatically resizing the Canvas as the enclosing Stage changes size can be encountered.

Approach

In the sample code provided, a custom class CanvasPane is utilized. This class wraps an instance of Canvas within a Pane. The layoutChildren() method is overridden to ensure that the dimensions of the canvas match those of the enclosing Pane.

Resizing Constraints

Note that Canvas returns false for its isResizable() property, indicating that it cannot be resized during layout by its parent. However, Pane does not perform layout beyond resizing resizable children to their preferred sizes. Hence, the initial size of the canvas is determined by its width and height arguments.

Key Differences from Original Example

This approach differs from using fully saturated colors by employing an array of color hues, which rotate with each animation cycle. Additionally, related examples demonstrate how to place controls on top of the animated background.

Code Implementation

<code class="java">public class Baubles extends Application {

    // ... code omitted ...

    private static class CanvasPane extends Pane {

        // ... code omitted ...

        @Override
        protected void layoutChildren() {
            // ... code omitted ...
            canvas.setWidth(w);
            canvas.setHeight(h);
        }
    }

    // ... code omitted ...
}</code>

This revised code incorporates the CanvasPane class, automatically resizing the Canvas within the parent container. As the Stage is resized, the Canvas will adjust its size accordingly, ensuring a seamless background animation.

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