Building a rocks and spaceship game with Pygame Zero

Establishing the screen area. Program code: ------------------------------------------------------ #set screen size WIDTH = 600 HEIGHT = 500 # function to draw things to the screen def draw(): screen.clear() Now save and run this part of the program. You should see a blank window pop up. File: spacraft_1.py Mention constants; functions

Now add the spacecraft There must be a directory (folder) named “images” in your current folder. In that folder there needs to be an image called ‘spacecraft.png’. We need two lines of code to define our spacecraft image, which is called an “Actor” in pygame zero, and to position the spacecraft on the screen. Code: # Create the actors spacecraft = Actor('spacecraft') # The spacecraft actor spacecraft.pos = WIDTH/2, HEIGHT/2 # The initial position of the spacecraft Place these lines before the draw function. Then you have to draw the Actor, so put this code in the draw function: Spacecraft.draw() More actors to come later

About objects and methods We need some definitions so we know what we’re talking about ‘spacecraft’ is being used as a name to define an “object”. Think of an object as a model of something real Objects have ‘data’ and ‘methods’ associated with them. A method controls the behavior of an object data is information about the object ‘spacecraft.draw()’ says to apply the draw method to object spacecraft. That does exactly what you expect. It draws the spacecraft. But where does it put it? spacecraft.pos is used to assign a value to the position data for ‘spacecraft’. So the screen height and width are each divided by two which gives coordinates for the center of the screen. ‘screen’ is an object built in to pygame zero. We had to define spacecraft to be an object of type “Actor”

OK, enough of the definitions already!

So now if we save and run the code to this point we get a spacecraft in the middle of the screen. Not much of a game yet, is it? So let’s learn to move the spacecraft.

The update function “update()” is executed by pygame zero 60 times per second (as is draw()) We want to use update() to process keystrokes The built in ‘keyboard’ object has data associated with it. The values ‘right’, ‘left’, ‘up’, and ‘down’ are either True or False depending on whether the appropriate key is pressed Remember the decisions with if tests in the gpio code

The spacecraft object has x and y coordinates associated with it that tell draw() where to put it on the screen. The spacecraft object has data describing where it’s left edge, right edge, top, and bottom are located on the screen So we can test to see if the appropriate edge of the screen is about to move off screen The code to do this is on the next slide. Put the update function after the draw function. The use of ‘and’ means both parts of the if test must be True for the whole statement to be True

# --------------------------------------- # The update function def update(): # If the cursor keys are pressed, then move the spacecraft. if keyboard.left: spacecraft.x -= 2 if keyboard.right: spacecraft.x += 2 if keyboard.down: spacecraft.y += 2 if keyboard.up: spacecraft.y -= 2 # This is fine except we can move offscreen… File: spacecraft_3.py Talk about += Why use 4 if statements rather than an if … elif. Diag movement. Show it with elifs. Then modify one line to test a boundry.

# --------------------------------------- # The update function def update(): # If the cursor keys are pressed, then move the # spacecraft within the limits of the screen. if keyboard.left and spacecraft.left > 2: spacecraft.x -= 2 if keyboard.right and spacecraft.right < WIDTH+2: spacecraft.x += 2 if keyboard.down and spacecraft.bottom < HEIGHT+2: spacecraft.y += 2 if keyboard.up and spacecraft.top > 2: spacecraft.y -= 2 So this stops us from moving offscreen. Discuss this.

A rock! Next let’s get a rock to appear and move across the screen. Later we will vary the starting position, direction, and speed of the rock. We will do this first in a new program and then we will pull that part into the spaceship program.

Code, name this program rock Code, name this program rock.py: # Set the size of the window WIDTH = 600 HEIGHT = 500 # Create the actors rock = Actor('rock') # Rock actor from rock image rock.pos = 0, 0 def draw(): screen.clear() rock.draw() def update(): rock.x += 1 rock.y += 1

Changing the rock’s path and speed Notice that the rock is moving at 45 degrees left to right across the screen. Why? Let’s change it to a shallower angle. How? Now let’s make it faster Move the starting point for the rock near the middle (how?) and try a subtraction on rock.x So how do make the rock start at some random point at the top of the screen?

random() function in python We want an integer, not a float (number with a decimal part) We use the randint method with the random function We want a random number from 0 to 600, so random.randint(0, 600) will give us one. Code: rock.pos = random.randint(0, WIDTH), 0 Show this in python shell

Libraries in python It’s not enough to just add the random.randint() statement, we have to tell python that we want to use the random library We do that with an “import” statement. This is usually the first thing in the program. Code: import random

Random direction and velocity We really want the rock to be different each time it shows up. So we can get random values to use in our update function. Code: x_change = random.randint(-5,5) # this makes the rock move either # left to right or right to left y_change = random.randint(1,5) # keeping to positive numbers # makes the rock always move down And make this change: def update(): rock.x += x_change rock.y += y_change

Bouncing off the edges We can look to see if our next position on the x axis is going to move off the edge of the screen and if so change the direction of motion. Code: if rock.x + x_change > 600: # about to leave the right edge x_change = -x_change # so reverse the x direction elif rock.x + x_change < 0: # about to leave the left wall Remember elif? Code is rock3.py. More on next slide

Local and global variables Variables declared in a function are local to that function. This means that only in the function where they are declared can these variables be seen or modified. Variable declared at the main program level can be seen anywhere in the program, but can only be modified from a function if the are declared as type global We can look at some examples Code: def update(): global x_change; global y_change;

Make the rocks keep falling! What we’d really like to see in a game is rocks falling one after the other. Let’s make that change by testing for the rock passing the bottom of the screen and then restarting it at the top when it does. Code: # let's check and see if we're going off the bottom of the screen if rock.y + x_change > 500: rock.pos = random.randint(0, WIDTH), 0 x_change = random.randint(-5,5) # this makes the rock move either # left to right or right to left y_change = random.randint(1,5) # keeping to positive numbers # makes the rock always move down File: rock4.py

Make the initial positioning code a function. The duplicate code can be made into a function and called from both places it is needed x_change and y_change need to be declared as globals in the function Now we don’t have to type it twice! Code: rocks5.py

Collisions If we are going to make a projectile to shoot at a rock then we have to be able to detect when the rock and the projectile hit each other For now, we will put a square on the screen and try to detect when the rock hits the square A method called “colliderect” will do this for us File: rock_6.py

Code, add this line ahead of rock =: rect_color = (255,0,0) Code, in def update() add this at end: if rock.colliderect(box): #change the rectangle's color rect_color = (255,255,255) Code, need to make rect_color a global in update(): global rect_color File: rock_6.py

A laser beam Let’s make a long, skinny rectangle that we can use as our ‘laser beam’ When we detect a collision between the rock and the laser beam, we will blow up the rock Code is on next slide

# Set the size of the window WIDTH = 600 HEIGHT = 500 def draw(): screen.clear() screen.draw.filled_rect(laser,(255,0,0)) #def update(): # a rectangle is defined by it's bottom left corner # Rect(bottom left x, bottom left y),(x distance, y distance)) laser = Rect((500, 400), (4, -390)) show file recttest.py. Make changes

Make the space bar shoot the laser Same type code as checking for arrow keys We use the schedule method for the built in clock object to cause a function to execute after the desired time has passed Code: def update(): global laser if keyboard.space: laser = Rect((500, 400), (4, -390)) #put the laser onscreen clock.schedule(laser_off, 1.0) # turn off after 1 second def laser_off(): # move the laser back off the screen laser = Rect((1500, 1400), (4, -390)) Code: laser2.py

Putting the pieces together Open a new file, lasergame.py Copy and paste in the spacecraft code Copy and paste the rock code below that Now we have to do some cleanup and eliminate some duplication. We are looking for the spaceship being moveable and a series of rocks falling all in one game Code: lasergame_1.py Use the rock code without the extra rectangle and collision detection (rock_5.py). Anyone who gets things in a mess can just download a copy from my web page.

We were using this code to test the laser: Next add the laser code and we will modify that to actually shoot from the spaceship Reminder: # a rectangle is defined by it's bottom left corner # Rect(bottom left x, bottom left y),(x distance, y distance)) We were using this code to test the laser: laser = Rect((500, 400), (4, -390)) #put the laser onscreen We want the laser to fire from the nose of the spaceship, so we need to find where that nose is located laser = Rect((spacecraft.x-2,0),(4,spacecraft.top)) This goes under “if keyboard.space:” for now File: lasergame_2.py

So need to make the laser follow the ship A problem: the laser fires and stays where it first appears, the ship can move So need to make the laser follow the ship To do that we need to redraw the laser every time we redraw the ship Code (near top of program): laser_firing = False #initialize laser to off Code (changes in update() function): if keyboard.space: laser_firing = True clock.schedule(laser_off, 1.0) # turn off after 1 second if laser_firing: # redraw the laser anytime it is firing laser = Rect((spacecraft.x-2,0),(4,spacecraft.top)) File: lasergame3.py

We need noise! Let’s add a sound for the laser firing Code (add to the keyboard.space section): sounds.laser.play() # play the laser.wav file This will play the file “laser.wav” from the “sounds” directory The file is available on my web site File: lasergame4.py

Collision Code (after the globals in update()): # Check to see if the rock has collided with the spacecraft collision = spacecraft.colliderect(rock) # If there has been a collision, then switch both actors to their destroyed versions if collision and spacecraft.image != ‘spacecraft_destroyed’: rock.image = 'rock_destroyed' spacecraft.image = 'spacecraft_destroyed' gameOver = True rockLaser = rock.colliderect(laser) # Check to see if the laser has hit the rock # If the laser has hit the rock and the rock has not already been # destroyed, then destroy the rock if rockLaser and rock.image != 'rock_destroyed': File: lasergame_5.txt

Reset the images rock.image = 'rock' Our rock and spaceship are now stuck in destroyed mode. Let’s do a quick and dirty fix on that We can set the rock and spacecraft to their initial image when we create a new rock Code (in setup_new_rock()): rock.image = 'rock' spacecraft.image = 'spacecraft' In the initialization code create BOTH actors before calling setup_new_rock() File: lasergame_6.py

Last but not least: Scores Let’s keep track of how many rocks are hit and how many spacecraft get destroyed Create 2 variables as globals in updates() and draw(): global rock_hits global spacecraft_hits Initialize them to 0 at beginning of program Increment appropriately in the collision if tests File: lasergame_7.py

This game has some problems… Rock should just go away and restart when it’s hit; that’s a pretty easy fix A spacecraft should either end the game or maybe count down the number of spacecraft left, assuming you get to start with more that one. We need a sound for the spacecraft being hit You can keep the laser firing constantly. It needs a “recharge period” What else?

We are done with pygame zero! At least, we are done with what I think I should show you for now Try making some of the changes listed on the previous slide on your program. I have put some other example programs on my web page; try modifying some of those if you like. For at least a while, you are on your own! Work on something of your choosing and we will be available to help you.