Cannonball and Slingshot - The Essential Guide to HTML5 - page 115

Code Explanation

var target = new Myrectangle(300,100,
80,200,"rgb(0,5,90)");

Build a Myrectangle object and assign to target

Build a Myrectangle object and assign to ground

var ground = new Myrectangle(0,300,
600,30,"rgb(10,250,0)");

everything.push(target);

Add target to everything

everything.push(ground); Add ground

everything.push(cball);

Add cball (which will be drawn last, so on top of other
stuff

function init(){ Header for init function

ctx = document.getElementById
('canvas').getContext('2d');

Set up ctx in order to draw on the canvas

drawall();

Draw everything

} Close init

function fire() { Head for fire function

cball.sx = iballx;

Reposition cball in x

cball.sy = ibally; Reposition cball in y

horvelocity = Number(document.
f.hv.value);

Set horizontal velocity from form. Make a number

verticalvel1 = Number(document.
f.vv.value);

Set initial vertical velocity from form

drawall(); Draw everything

tid = setInterval
(change,100);

Start timing event

return false;

Return false to prevent refresh of HTML page

} Close function