import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.WritableImage;
import javafx.scene.input.MouseEvent;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class TestAlternatingImages extends Application {
    public static int IMGW = 3;
    public static int IMGH = 3;
    public static int ROWS = 150;
    public static int COLS = 500;
    public static int SEP = 0;
    public static int BORDER = 5;

    Scene scene;
    Group root;
    Rectangle bg;
    ImageView views1[] = new ImageView[ROWS * COLS];
    ImageView views2[] = new ImageView[ROWS * COLS];
    ImageView viewsall[] = new ImageView[ROWS * COLS * 2];
    boolean alternating;

    int interp(double a, double b, double t) {
        double v = a + (b-a) * t;
        return (int) Math.round(v * 255);
    }

    int interp(Color a, Color b, double t) {
        return (0xff << 24 |
                interp(a.getRed(),   b.getRed(),   t) << 16 |
                interp(a.getGreen(), b.getGreen(), t) <<  8 |
                interp(a.getBlue(),  b.getBlue(),  t));
    }

    @Override
    public void start(Stage stage) {
        WritableImage wimg1 = new WritableImage(IMGW, IMGH);
        WritableImage wimg2 = new WritableImage(IMGW, IMGH);
        for (int y = 0; y < IMGH; y++) {
            for (int x = 0; x < IMGW; x++) {
                double t = Math.sqrt((x * x + y * y) / (double) (IMGW * IMGW + IMGH * IMGH));
                wimg1.getPixelWriter().setArgb(x, y, interp(Color.RED, Color.GREEN, t));
                wimg2.getPixelWriter().setArgb(x, y, interp(Color.BLUE, Color.YELLOW, t));
            }
        }

        root = new Group();
        bg = new Rectangle(COLS * (IMGW + SEP) + BORDER*2 - SEP,
                           ROWS * 2 * (IMGH + SEP) + BORDER * 3 - SEP*2);
        System.out.println("dims = "+bg.getWidth()+" x "+bg.getHeight());
        root.getChildren().add(bg);
        double ox1 = BORDER;
        double oy1 = BORDER;
        double ox2 = BORDER;
        double oy2 = BORDER * 2 + ROWS * (IMGH + SEP);
        for (int r = 0; r < ROWS; r++) {
            for (int c = 0; c < COLS; c++) {
                ImageView iv1 = new ImageView(wimg1);
                iv1.setX(ox1 + c * (IMGW + SEP));
                iv1.setY(oy1 + r * (IMGH + SEP));
                ImageView iv2 = new ImageView(wimg2);
                iv2.setX(ox2 + c * (IMGW + SEP));
                iv2.setY(oy2 + r * (IMGH + SEP));
                int index = r * COLS + c;
                views1[index] = iv1;
                views2[index] = iv2;
                viewsall[index * 2 + 0] = iv1;
                viewsall[index * 2 + 1] = iv2;
            }
        }
        loadImagesAdjacent();

        scene = new Scene(root);
        stage.setScene(scene);
        stage.show();

        scene.addEventHandler(MouseEvent.MOUSE_PRESSED, new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                alternating = !alternating;
                if (alternating) {
                    loadImagesAlternating();
                } else {
                    loadImagesAdjacent();
                }
            }
        });

        AnimationTimer timer = new AnimationTimer() {
            @Override
            public void handle(long l) {
                run();
            }
        };
        timer.start();

    }

    double hue;
    long start;
    int frames;
    public void run() {
        hue += 1;
        if (hue >= 360) hue -= 360;
        bg.setFill(Color.hsb(hue, 1.0, 1.0));
        long now = System.currentTimeMillis();
        if (start == 0) {
            start = now;
            frames = 0;
        } else {
            frames++;
            double seconds = (now - start) / 1000.0;
            if (seconds >= 1.0) {
                System.out.println("FPS: "+(frames / seconds));
                start = now;
                frames = 0;
            }
        }
    }

    void loadImagesAdjacent() {
        root.getChildren().clear();
        root.getChildren().add(bg);
        root.getChildren().addAll(views1);
        root.getChildren().addAll(views2);
    }

    void loadImagesAlternating() {
        root.getChildren().clear();
        root.getChildren().add(bg);
        root.getChildren().addAll(viewsall);
    }
}