# file: checks.py
#
# date: Oct. 25, 2007
#
# author: CS074 Digital World; Fall 2007
# 
import turtle

def setup(w, h):
	turtle.setup(width=w, height=h)
	turtle.degrees()
	turtle.up()         # turtle pen is up! Otherwise too slow.

# check is responsible for drawing an individual colored check at (x,y).
#
def check(x, y, height, width, color):

	turtle.color(color)
	turtle.goto(x, y)

	turtle.begin_fill()
	turtle.goto(x+width, y)
	turtle.goto(x+width, y+height)
	turtle.goto(x, y+height)
	turtle.goto(x, y)
	turtle.end_fill()

# rowOfChecks will draw a row of cols checks across the turtle window at the
# specified y coordinate. The checks will alternate in color between color1
# and color2. rowOfChecks also accepts a colorFlag which determines which of
# the two colors are used for the first (i.e., leftmost) check in the row.
# This function returns the value of colorFlag to help with managing the
# starting color of the next row.
#
def rowOfChecks(y, cols, checkHeight, color1, color2, colorFlag):

	windowWidth = turtle.window_width()

	right = windowWidth / 2
	left = -right

	checkWidth = windowWidth / cols

	x = left;

	while x < right:

		# We're now ready to draw a check. NB: that the color
		# is determined by the status of the boolean flag colorFlag.
		#
		if colorFlag:
			check(x, y, checkHeight, checkWidth, color1)
		else:
			check(x, y, checkHeight, checkWidth, color2)

		x = x + checkWidth

		# The next check to the right should have the other color.
		#
		colorFlag = not(colorFlag)

	# We're returning the value of colorFlag to deal with even .vs. odd
	# row lengths.
	#
	return colorFlag

# checks will draw a rows x cols checkerboard covering the entire turtle window.
# The colors for the checks are specified in color1 and color2.
#
def checks(rows, cols, color1, color2):

	windowHeight = turtle.window_height()

	top = windowHeight / 2
	bottom = -top

	checkHeight = windowHeight / rows

	y = top - checkHeight

	# We'll use a colorFlag to manage the alternation between the two colors.
	#
	colorFlag = True

	while y >= bottom:

		colorFlag = rowOfChecks(y, cols, checkHeight, color1, color2, colorFlag)

		y = y - checkHeight
		
		# If there is an odd number of columns, then the next row should start
		# with the same color that ended the just completed row.
		#
		if cols % 2 == 0:
			colorFlag = not(colorFlag)