#assume a square grid
gridWidth = 20
gridInc = 1
showAxes = True

#set the range of x-values
xmin = -gridWidth/2
xmax = gridWidth/2

#range of y-values
ymin = -gridWidth/2
ymax = gridWidth/2

#calculate the range
rangex = xmax - xmin
rangey = ymax - ymin

t = 0
initialRadius = 3

circleList = []


def setup():
    global xscl, yscl, radius
    size(600,600)
    xscl = width/rangex
    yscl = -height/rangey
    colorMode(HSB, 360, 100, 100)
    radius = initialRadius
    
#end function setup

def draw():
    global xscl, yscl, t, circleList, initialRadius, radius
    background(0, 0, 100) #white
    translate(width/2, height/2)
    grid(xscl, yscl)
    center = (-6, 0)
    inc = .01
    radius = 3
    # radius -= inc
    # if radius < .5:
    #     radius = initialRadius + inc
    hsb = (90, 50, 50)
    drawCircle(center, initialRadius, hsb)
    
    #orbiting circle
    fill(60, 100, 100)
    dotRad = .075*radius
    x = (center[0] + (radius)*cos(t))*xscl
    y = (center[1] + (radius)*sin(t))*yscl
    #x = (center[0] + (radius))*xscl
    #y = (center[1] + (radius))*yscl
    ellipse(x, y, 2*dotRad*xscl, 2*dotRad*yscl)
    circleList = [y] + circleList[:249]
    
    
    #line
    stroke(240, 100, 100)
    line(x, y, 2*xscl, y)
    ellipse(2*xscl, y, 2*dotRad*xscl, 2*dotRad*yscl)
    
    #loop over circleList to leave a trail
    fill(0, 100, 100)
    noStroke()
    for i in range(len(circleList)):
        #small circle for trail:
            ellipse(i+ 2*xscl, circleList[i], .25*xscl, .25*xscl)
    
    t += .05
    
    
    
#end function draw
    
def grid(xscl, yscl):
    #draws a grid for graphing
    #cyan lines
    strokeWeight(1)
    stroke(200, 100, 100) #lightBlue
    
    #vertical lines
    for i in range(xmin, xmax + 1):
        line(i*xscl, ymin*yscl, i*xscl, ymax*yscl)
        
    #horizontal lines
    for i in range(ymin, ymax + 1):
        line(xmin*xscl, i*yscl, ymax*xscl, i*yscl)
    
    if showAxes:
        axes()
    
#end function grid

def axes():
    stroke(0, 0, 0) #black
    strokeWeight(2)
    #y axis
    line(0, ymin*yscl, 0, ymax*yscl)
    #x axis
    line(xmin*xscl, 0, xmax*xscl, 0)
#end function axes

def drawCircle(center, radius, hsb):
    h = center[0] * xscl
    k = center[1] * yscl
    radius *= xscl
    diam = radius*2
    fill(hsb[0], hsb[1], hsb[2])
    ellipse(h, k, diam, diam)