Draw bezier curve using Processing.py

bezier_curve.py

# Libraries
import time

# Points
p = [{"x" : 100, "y" : 300}, {"x" : 500, "y" : 100}, {"x" : 700, "y" : 300}]
# default values
prev_x = p[0]['x']
prev_y = p[0]['y']
t = 0

def setup():
    """First called function to setup environment
    """
    # size of window
    size(900, 500)
    # background color
    background(255, 255, 255)
    # function to setup bezier prerequisites    
    setup_bezier()
    
def draw():
    """The main drawing function, called iteratilvely.
    """
    # calling some global variables
    global prev_x, prev_y, t
    # setting the stroke weight for curve
    strokeWeight(3)
    # Slow down the processing - otherwise it will be over in a jiffy !!
    time.sleep(0.01)
    # stroke color - a splash of reddish
    stroke(190, 0, 0)
    # find the next bt
    next_x, next_y = find_next_bt(t)
    # draw line of curve
    line(prev_x, prev_y, next_x, next_y)
    # replace prev with next
    prev_x = next_x
    prev_y = next_y
    # increment the t
    t += 0.01
    # stopping critera
    if t > 1.01:
        # stop calls to draw()
        noLoop()

def drawPoint(i, textOffset = 10):
    # set the stroke
    stroke(0)
    # set the weight of stroke
    strokeWeight(7)
    # draw point
    point(p[i]['x'], p[i]['y'])
    # fill point with black color
    fill(0)
    # draw text - string and point of placement
    text("P{0}".format(i), p[i]['x'] + textOffset, p[i]['y'] + textOffset)
    
def setup_bezier():
    """Creates anchor & control points and draws lines between them
    """
    # Step 1: Draw the achor and control points
    for i in range(3):
        drawPoint(i)
    # Step 2: Draw the lines between the control and anchor points
    # stroke color
    stroke(150)
    # width of stroke
    strokeWeight(1)
    # draw line between p0 and p1
    line(p[0]['x'], p[0]['y'], p[1]['x'], p[1]['y'])
    # draw line between p1 and p2
    line(p[1]['x'], p[1]['y'], p[2]['x'], p[2]['y'])
    

def find_next_bt(t):
    """Computes the next iteration point of quadratic bezier curve
    """ 
    # calulate the x-axis
    x = (1 - t) * (1 - t) * p[0]['x'] + 2 * (1 - t) * t * p[1]['x'] + t * t * p[2]['x'];
    # calulate the y-axis
    y = (1 - t) * (1 - t) * p[0]['y'] + 2 * (1 - t) * t * p[1]['y'] + t * t * p[2]['y'];
    # return
    return x, y