Creating the Shape

• The template file automatically creates the scene to below when run
• Your initial task is to add the classic yellow Pacman shape to the center of the screen
  • Consists of a circle missing a 90 deg segment centered on the positive x-axis
• Recall when working with GArcs how you need to specify the location! That will be important for getting Pacman properly centered

Something to smile about

Fillable Arcs

• The GArc class is a GFillableObject, and so you can call .set_filled() on a GArc object
• Filled like a pie-shaped wedge formed between the center of the bounding box and the starting and end points of the arc

def filled_arc():
    gw = GWindow(400, 400)
    arc = GArc(50, 50, 
               350, 350, 
               90, 135)
    arc.set_color("orange")
    arc.set_filled(True)
    gw.add(arc)

Part A: Pacman Created

def create_pacman():
    pacman = GArc(
        GW_WIDTH / 2 - PACMAN_RADIUS,  #centered x
        GW_HEIGHT / 2 - PACMAN_RADIUS, #centered y
        2 * PACMAN_RADIUS,             #width
        2 * PACMAN_RADIUS,             #height
        45,                            #starting angle
        270,                           #sweep angle
    )
    pacman.set_filled(True)
    pacman.set_fill_color("yellow")
    return pacman

pacman = create_pacman()
gw.add(pacman)

Moving in a single direction

• The next task is to get Pacman moving!
• Create a step callback function and define an interval event listener to call that function every 20 ms
• Each time the step function is called, it should move Pacman forward (to the right) by the number of pixels indicated by the provided constant

Part B: Pacman Moved

def step():
    pacman.move(PACMAN_SPEED, 0)

gw.set_interval(step, 20)

Flipping at the edges

Bouncing Visualized

Pseudo Bouncing

• In pseudocode, you might have something like:

def step():
    pacman.move(|||something involving the direction|||, 0)

    if |||left or right edge of Pacman extends off screen|||:
        |||reverse Pacman direction by switching direction variable value|||
        |||turn Pacman around by changing starting angle of arc|||

|||initialize direction variable|||
gw.set_interval(step, 20)

Pacman Bounced

def step():
    pacman.move(gw.dx, 0)
    if (pacman.get_x() + 2 * PACMAN_RADIUS > GW_WIDTH #right edge
        or pacman.get_x() < 0 #left edge
       ):
        gw.dx *= -1 #flip it
        pacman.set_start_angle(pacman.get_start_angle() + 180)

pacman = create_pacman()
gw.dx = PACMAN_SPEED
gw.set_interval(step, 20)

Finding the Pills

• At the moment Pacman just moves over the yellow pills: we’d like to change that so that they actually disappear as Pacman moves over them
• You can remove anything from the GWindow with gw.remove(obj), but that requires you to have a variable obj that was assigned your particular GObject.
  • Here we have named variables for Pacman (pacman) and for the background colored rectangle (bg), but not the pills!
• So a method is needed to retrieve a GObject that has already been added to the window
  • The most obvious of these is the .get_element_at(x,y) method for GWindows.

Getting Elements

• You provide .get_element_at(x,y) a pair of coordinates, \(x\) and \(y\)
  • If there is a GObject at that location, it will return it to you! So save that object in a variable!
  • If there is no object at that location, it will return None
• You can then use any returned object exactly as you would had you assigned it to a variable initially, including removing it from the window!

>>> leftmost_pill = gw.get_element_at(20, 200)
>>> print(leftmost_pill)
GOval(20, 190.0, 20, 20)

Pacman’s Mouth

Hunger Visualized

Hunger Satiated

def step():
    ...
    # Adjusting for which side mouth is on
    if gw.dx > 0:
        x = pacman.get_x() + PACMAN_RADIUS * 1.5
    else:
        x = pacman.get_x() + PACMAN_RADIUS * 0.5
    y = pacman.get_y() + PACMAN_RADIUS
    # Getting anything there
    obj = gw.get_element_at(x,y)
    # Removing that thing if present and if it isn't the bg
    if obj is not None and obj is not bg:
        gw.remove(obj)
    ...

Challenge!

• Currently, Pacman’s mouth doesn’t move
• Add code to cause Pacman’s mouth to repeatedly open and close by adjusting the starting angle and sweep angle every step
• You’ll need to adjust both angles in tandem to achieve a symmetric opening and closing of the mouth