Cannonball and Slingshot - The Essential Guide to HTML5 - page 114

Code Explanation

}

Close the function

function moveball(dx,dy) { Header for the moveball function

this.sx +=dx; Increment the sx property by dx

Increment the sy property by dy

this.sy +=dy;

} Close function

var cball = new Ball(iballx,ibally,
10,"rgb(250,0,0)");

Create a new Ball object at the indicated position,
radius, and color. Assign it to the variable cball . Note
that nothing is drawn at this time. The information is just
set up for later use.

function Myrectangle(sx,sy,swidth,
sheight,stylestring) {

Header for function to construct a Myrectangle object

Sets the sx property of THIS object

this.sx = sx;

this.sy = sy; … sy

this.swidth = swidth; … swidth

this.sheight = sheight;

… sheight

this.fillstyle = stylestring; … stylestring

this.draw = drawrects;

… draw . This sets up a method that can be invoked.

this.moveit = moveball; …. moveit . This sets up a method that can be invoked.

It is not used in this program.

}

Close Myrectangle function

function drawrects() { Header for drawrects function

ctx.fillStyle = this.fillstyle; Set the fillStyle

ctx.fillRect(this.sx,this.sy,
this.swidth,this.sheight);

Draw the rectangle using the object properties

}

Close function