Bouncing Circles

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import java.util.Arrays; import java.util.Random; import java.util.function.DoubleSupplier; import javafx.animation.AnimationTimer; import javafx.application.Application; import javafx.beans.InvalidationListener; import javafx.scene.Scene; import javafx.scene.layout.BorderPane; import javafx.scene.layout.Pane; import javafx.scene.paint.Color; import javafx.scene.shape.Circle; import javafx.stage.Stage; public class Main extends Application { public static void main(String[] args) { launch(args); } final Color fill = new Color(1, 1, 1, 00.05); double width, height; Circle[] circles = new Circle[0]; double[][] moveBy = new double[0][2]; double[] radiusDivs = new double[0]; @Override public void start(Stage stage) throws Exception { Random random = new Random(); Pane pane = new Pane(); pane.setStyle("-fx-background-color:derive(black, 30%);"); Scene scene = new Scene(new BorderPane(pane), 300, 300); stage.setScene(scene); stage.show(); DoubleSupplier randomFraction = () -> (random.nextBoolean() ? 1 : -1) * random.nextDouble(); InvalidationListener resizeListener = e -> { double oldW = width; double oldH = height; width = stage.getWidth(); height = stage.getHeight(); double min = Math.min(width, height); double max = Math.max(width, height); int size = (int) Math.sqrt(max); int sizePrev = circles.length; circles = sizePrev == size ? circles : Arrays.copyOf(circles, size); radiusDivs = sizePrev == size ? radiusDivs : Arrays.copyOf(radiusDivs, size); moveBy = sizePrev == size ? moveBy : Arrays.copyOf(moveBy, size); if (sizePrev < size) { for (int i = sizePrev; i < size; i++) { Circle c = circles[i] = new Circle(5, fill); c.getStyleClass().add("circles"); double r = radiusDivs[i] = 0.5 + random.nextDouble(); c.setRadius((min / 10) * radiusDivs[i]); c.setCenterX(r + random.nextInt((int) (width - r))); c.setCenterY(r + random.nextInt((int) (height - r))); moveBy[i] = new double[] { randomFraction.getAsDouble(), randomFraction.getAsDouble() }; } } int limit = sizePrev > size ? size : sizePrev; for (int i = 0; i < limit; i++) { Circle c = circles[i]; c.setRadius((min / 10) * radiusDivs[i]); c.setCenterX(width * (c.getCenterX() / oldW)); c.setCenterY(height * (c.getCenterY() / oldH)); } pane.getChildren().setAll(circles); }; stage.widthProperty().addListener(resizeListener); stage.heightProperty().addListener(resizeListener); resizeListener.invalidated(null); new AnimationTimer() { @Override public void handle(long now) { for (int i = 0; i < circles.length; i++) { Circle c = circles[i]; double x = c.getCenterX(); double y = c.getCenterY(); double r = c.getRadius(); if (x - r < 0) moveBy[i][0] = random.nextDouble(); else if (x + r > width) moveBy[i][0] = -1 * random.nextDouble(); if (y - r < 0) moveBy[i][1] = random.nextDouble(); else if (y + r > height) moveBy[i][1] = -1 * random.nextDouble(); c.setCenterX(x + moveBy[i][0]); c.setCenterY(y + moveBy[i][1]); } } }.start(); } }

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