yPos = 0.0

def setup():  # setup() runs once
    size(200, 200)

def draw():  # draw() loops forever, until stopped
    yPos = yPos - 1.0
    if yPos < 0:
        yPos = height
    line(0, yPos, width, yPos)
def setup():
    size(200, 200)
# Although empty here, draw() is needed so
# the sketch can process user input events
# (mouse presses in this case).

def draw():

def mousePressed():
    line(mouseX, 10, mouseX, 90)
Description After setup() has been called, the draw() function is repeatedly invoked until the program is stopped or noLoop() is called. draw() is called automatically and should never be called explicitly.

It should always be controlled with noLoop(), redraw() and loop(). If noLoop() is used to stop the code in draw() from executing, then redraw() will cause the code inside draw() to be executed a single time, and loop() will cause the code inside draw() to resume executing continuously.

The number of times draw() executes in each second may be controlled with the frameRate() function.

It is common to call background() near the beginning of the draw() loop to clear the contents of the window, as shown in the first example above. Since pixels drawn to the window are cumulative, omitting background() may result in unintended results, especially when drawing anti-aliased shapes or text.

There can only be one draw() function for each sketch, and draw() must exist if you want the code to run continuously, or to process events such as mousePressed(). Sometimes, you might have an empty call to draw() in your program, as shown in the second example above.
def draw():
Related setup()
Updated on Tue Jul 11 06:52:23 2017.
Creative Commons License