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// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/11/Pong/Ball.jack
/**
* A graphical ball. Characterized by a screen location and distance of
* last destination. Has methods for drawing, erasing and moving on the screen.
* The ball is displayed as a filled, 6-by-6 pixles rectangle.
*/
class Ball {
field int x, y; // the ball's screen location (in pixels)
field int lengthx, lengthy; // distance of last destination (in pixels)
field int d, straightD, diagonalD; // used for straight line movement computation
field boolean invert, positivex, positivey; // (same)
field int leftWall, rightWall, topWall, bottomWall; // wall locations
field int wall; // last wall that the ball was bounced off of
/** Constructs a new ball with the given initial location and wall locations. */
constructor Ball new(int Ax, int Ay,
int AleftWall, int ArightWall, int AtopWall, int AbottomWall) {
let x = Ax;
let y = Ay;
let leftWall = AleftWall;
let rightWall = ArightWall - 6; // -6 for ball size
let topWall = AtopWall;
let bottomWall = AbottomWall - 6; // -6 for ball size
let wall = 0;
do show();
return this;
}
/** Deallocates the Ball's memory. */
method void dispose() {
do Memory.deAlloc(this);
return;
}
/** Shows the ball. */
method void show() {
do Screen.setColor(true);
do draw();
return;
}
/** Hides the ball. */
method void hide() {
do Screen.setColor(false);
do draw();
return;
}
/** Draws the ball. */
method void draw() {
do Screen.drawRectangle(x, y, x + 5, y + 5);
return;
}
/** Returns the ball's left edge. */
method int getLeft() {
return x;
}
/** Returns the ball's right edge. */
method int getRight() {
return x + 5;
}
/** Computes and sets the ball's destination. */
method void setDestination(int destx, int desty) {
var int dx, dy, temp;
let lengthx = destx - x;
let lengthy = desty - y;
let dx = Math.abs(lengthx);
let dy = Math.abs(lengthy);
let invert = (dx < dy);
if (invert) {
let temp = dx; // swap dx, dy
let dx = dy;
let dy = temp;
let positivex = (y < desty);
let positivey = (x < destx);
}
else {
let positivex = (x < destx);
let positivey = (y < desty);
}
let d = (2 * dy) - dx;
let straightD = 2 * dy;
let diagonalD = 2 * (dy - dx);
return;
}
/**
* Moves the ball one unit towards its destination.
* If the ball has reached a wall, returns 0.
* Else, returns a value according to the wall:
* 1 (left wall), 2 (right wall), 3 (top wall), 4 (bottom wall).
*/
method int move() {
do hide();
if (d < 0) { let d = d + straightD; }
else {
let d = d + diagonalD;
if (positivey) {
if (invert) { let x = x + 4; }
else { let y = y + 4; }
}
else {
if (invert) { let x = x - 4; }
else { let y = y - 4; }
}
}
if (positivex) {
if (invert) { let y = y + 4; }
else { let x = x + 4; }
}
else {
if (invert) { let y = y - 4; }
else { let x = x - 4; }
}
if (~(x > leftWall)) {
let wall = 1;
let x = leftWall;
}
if (~(x < rightWall)) {
let wall = 2;
let x = rightWall;
}
if (~(y > topWall)) {
let wall = 3;
let y = topWall;
}
if (~(y < bottomWall)) {
let wall = 4;
let y = bottomWall;
}
do show();
return wall;
}
/**
* Bounces off the current wall: sets the new destination
* of the ball according to the ball's angle and the given
* bouncing direction (-1/0/1=left/center/right or up/center/down).
*/
method void bounce(int bouncingDirection) {
var int newx, newy, divLengthx, divLengthy, factor;
// dividing by 10 first since results are too big
let divLengthx = lengthx / 10;
let divLengthy = lengthy / 10;
if (bouncingDirection = 0) { let factor = 10; }
else {
if (((~(lengthx < 0)) & (bouncingDirection = 1)) | ((lengthx < 0) & (bouncingDirection = (-1)))) {
let factor = 20; // bounce direction is in ball direction
}
else { let factor = 5; } // bounce direction is against ball direction
}
if (wall = 1) {
let newx = 506;
let newy = (divLengthy * (-50)) / divLengthx;
let newy = y + (newy * factor);
}
else {
if (wall = 2) {
let newx = 0;
let newy = (divLengthy * 50) / divLengthx;
let newy = y + (newy * factor);
}
else {
if (wall = 3) {
let newy = 250;
let newx = (divLengthx * (-25)) / divLengthy;
let newx = x + (newx * factor);
}
else { // assumes wall = 4
let newy = 0;
let newx = (divLengthx * 25) / divLengthy;
let newx = x + (newx * factor);
}
}
}
do setDestination(newx, newy);
return;
}
}
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