Cannonball and Slingshot - The Essential Guide to HTML5 - page 125

Code Explanation

}

function drawall() {

ctx.clearRect(0,0,cwidth,cheight);

var i;

for (i=0;i<everything.length;i++) {

var ob = everything[i];

Extract array for object

if (ob[1]) {

Need to translate and rotate?

ctx.save(); Save original axes

ctx.translate(ob[3],ob[4]);

Do indicated translation

ctx.rotate(ob[2]); Do indicated rotation

ctx.translate(-ob[3],-ob[4]);

Translate back

ob[0].draw(); Draw object

ctx.restore(); }

Restore axes

else { Else (no rotation)

ob[0].draw();} Do drawing

}

Close for loop

} Close function

function change() {

var dx = horvelocity;

verticalvel2 =verticalvel1 + gravity;

var dy=(verticalvel1 + verticalvel2)*.5;