import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.input.MouseEvent;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class TestBufferClear extends Application {
    Canvas c;
    GraphicsContext gc;
    double curx, cury;
    static boolean intermediate = true;

    public void start(Stage stage) {
        c = new Canvas(500, 500);
        curx = 250;
        cury = 250;
        draw(curx, cury);
        
        Scene scene = new Scene(new Group(c));
        scene.addEventHandler(MouseEvent.MOUSE_DRAGGED, new EventHandler<MouseEvent>() {
            public void handle(MouseEvent event) {
                double prevx = curx;
                double prevy = cury;
                double nextx = event.getSceneX();
                double nexty = event.getSceneY();
                double dx = nextx - prevx;
                double dy = nexty - prevy;
                double numsteps = Math.ceil(Math.max(Math.abs(dx), Math.abs(dy)));
                dx /= numsteps;
                dy /= numsteps;
                if (intermediate) {
                    for (int i = 1; i < numsteps; i++) {
                        prevx += dx;
                        prevy += dy;
                        draw(prevx, prevy);
                    }
                }
                draw(nextx, nexty);
                curx = nextx;
                cury = nexty;
            }
        });

        stage.setScene(scene);
        stage.setTitle(intermediate
                       ? "Rendering on every intermediate pixel"
                       : "Rendering only at mouse coordinates");
        stage.show();
    }

    public void draw(double x, double y) {
        gc = c.getGraphicsContext2D();

        gc.setFill(Color.WHITE);
        gc.fillRect(0, 0, 500, 500);
        gc.setStroke(Color.BLUE);
        gc.stroke();
        gc.beginPath();
        gc.moveTo(x, y);
        for (int i = 0; i < 500; i++) {
            double dx = Math.random() * 50 - 25;
            double dy = Math.random() * 50 - 25;
            gc.lineTo(x + dx, y + dy);
        }
        gc.setStroke(Color.GREEN);
        gc.stroke();
    }

    public static void main(String argv[]) {
        intermediate = (argv.length == 0);
        launch(argv);
    }
}