Arduino Uno Quick Start Manual page 139

if (next_x_pos >= paddle_x &&
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next_x_pos <= paddle_x + Game.paddle.width)
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{
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Game.ball.vy *= -1;
25
next_y_pos = paddle_y - Game.ball.diameter;
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}
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}
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$("#ball").css({ "left" : next_x_pos, "top" : next_y_pos });
30
}
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function movePaddle() {
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if (Game.controller.moveLeft) {
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var paddle_x = $("#paddle").position().left;
35
if (paddle_x - Game.paddle.speed >= 0) {
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$("#paddle").css("left", paddle_x - Game.paddle.speed);
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} else {
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$("#paddle").css("left", 0);
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}
40
}
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if (Game.controller.moveRight) {
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var paddle_x = $("#paddle").position().left;
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var next_pos = paddle_x + Game.paddle.width + Game.paddle.speed;
45
if (next_pos < Game.playfield.width) {
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$("#paddle").css("left", paddle_x + Game.paddle.speed);
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}
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}
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}
50
The most useful jQuery method when moving objects is
object that contains an HTML element s current
these attributes specify an object s x- and y-coordinates on the screen. In
lines 2 to 4 of the moveBall
the ball s current screen coordinates. In the following two lines, we calculate
the ball s new position by adding the current velocities for both directions.
After that, we check whether the ball s new position would be out of the screen.
If yes, we clip the coordinates to the screen s boundaries. In lines 8 to 14, we
make sure that the ball s x-coordinate is greater than zero and less than the
playfield s width. If the ball hits the left or right boundary of the playfield, we
multiply by -1, so it changes its direction.
vx
Nearly the same happens in lines 16 to 28 for the ball s y-coordinate. When-
ever the ball hits the top of the playfield, we multiply
has no bottom boundary, but we have to check whether the ball would hit
the paddle. If it does, we invert
left
function, we use the position
vy , too.
www.it-ebooks.info
Creating the Game
position . It returns an
and top attributes. In CSS,
function to determine
vy by -1. The playfield
121
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