Spork Editor

/*
Implicit Line and Circle
This example uses an implicit representations of
a line and a circle to draw a picture. 5000 circles 
are placed at random locations. Points inside a specific 
circle are colored green. Points above the line are 
colored red. Points below the line are colored blue.

Colors include transparency to give a blending effect.
*/

/*
This function uses the imlicit definition of a line
(y-y1)*(x2-x1)-(x-x1)*(y2-y1)=0
connecting (x1,y1) and (x2,y2). A positive return 
value puts (x,y) on one side of the line. A negative
value puts it on the other.
*/
function impLine(x,y,x1,y1,x2,y2){
  return((y-y1)*(x2-x1)-(x-x1)*(y2-y1));
}

/*
This function uses the implicit definition of a circle
(x-x1)*(x-x1)+(y-y1)*(y-y1)-r*r=0
centered at (x1,y1) with radius r. A positive return
value means that (x,y) is outside of the circle. A 
negative value puts (x,y) inside the circle.
*/
function impCircle(x,y,x1,y1,r){
  return((x-x1)*(x-x1)+(y-y1)*(y-y1)-r*r);
}