package com.example.a2ddrawdemo;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.view.View;

public class DrawView extends View {
    private int xMin = 0;          // This view's bounds
    private int xMax;
    private int yMin = 0;
    private int yMax;
    private float ballRadius = 80; // Ball's radius
    private float ballX = ballRadius + 20;  // Ball's center (x,y)
    private float ballY = ballRadius + 40;
    private float ballSpeedX = 5;  // Ball's speed (x,y)
    private float ballSpeedY = 3;
    private RectF ballBounds;      // Needed for Canvas.drawOval
    private Paint paint;           // The paint (e.g. style, color) used for drawing

    // Constructor
    public DrawView(Context context) {
        super(context);
        ballBounds = new RectF();
        paint = new Paint();
    }

    // Called back to draw the view. Also called by invalidate().
    @Override
    protected void onDraw(Canvas canvas) {
        // Draw the ball
        ballBounds.set(ballX-ballRadius, ballY-ballRadius, ballX+ballRadius, ballY+ballRadius);
        paint.setColor(Color.GREEN);
        canvas.drawOval(ballBounds, paint);

        // Update the position of the ball, including collision detection and reaction.
        update();

        // Delay
        try {
            Thread.sleep(30);
        } catch (InterruptedException e) { }

        invalidate();  // Force a re-draw
    }

    // Detect collision and update the position of the ball.
    private void update() {
        // Get new (x,y) position
        ballX += ballSpeedX;
        ballY += ballSpeedY;
        // Detect collision and react
        if (ballX + ballRadius > xMax) {
            ballSpeedX = -ballSpeedX;
            ballX = xMax-ballRadius;
        } else if (ballX - ballRadius < xMin) {
            ballSpeedX = -ballSpeedX;
            ballX = xMin+ballRadius;
        }
        if (ballY + ballRadius > yMax) {
            ballSpeedY = -ballSpeedY;
            ballY = yMax - ballRadius;
        } else if (ballY - ballRadius < yMin) {
            ballSpeedY = -ballSpeedY;
            ballY = yMin + ballRadius;
        }
    }

    // Called back when the view is first created or its size changes.
    @Override
    public void onSizeChanged(int w, int h, int oldW, int oldH) {
        // Set the movement bounds for the ball
        xMax = w-1;
        yMax = h-1;
    }
}