CHAPTER 4
Code Explanation
function drawall() { Function header for drawall
ctx.clearRect
(0,0,cwidth,cheight);
Erase canvas
var i; Declare var i for the for loop
for (i=0;i<everything.length;i++)
{
For each item in everything array...
everything[i].draw();} ...invoke the object's draw method. Close for loop.
} Close function
function change() { Header for change function
var dx = horvelocity; Set dx to be horvelocity
verticalvel2 =
verticalvel1 + gravity;
Compute new vertical velocity (add gravity)
var dy = (verticalvel1 +
verticalvel2)*.5;
Compute average velocity for the time interval
verticalvel1 = verticalvel2; Now set old to be new
cball.moveit(dx,dy); Move cball computed amount
var bx = cball.sx; Set bx to simplify the if
var by = cball.sy; ... and by
if ((bx>=target.sx)&&(bx<=
(target.sx+target.swidth))&&
Is the ball within the target horizontally...
(by>=target.sy)&&(by<=
(target.sy+target.sheight))) {
and vertically?
clearInterval(tid); If so, stop motion
} Close if true clause
if (by>=ground.sy) { Is the ball beyond ground?