--- title: "Catch and score" subtitle: "Games with microStudio · A whole game · Lesson 4" --- # Catch and score **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** A game is a loop, things that move, and one question asked every frame: are these two touching? :::teacher-note **In one sentence:** Students put the paddle and the stars together, test touching with abs() and and, see why a caught star must restart, fix a score that sets instead of adds, then add lives, a game over, a restart on Space, and a power-up of their own. **Students should be able to say:** I can check whether two things touch, every frame. I can keep a score and lives, and end the game when the lives run out. I can start a game again by calling init(). **Width:** the unmarked parts are the floor every student does (predict, run, investigate and make). Typical adds the modify practice; wider adds the real-world contexts. They add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Predict `abs()` gives a distance without its sign: `abs(-4)` is `4`. Work out each distance across and up. ```python def touches(sx, sy, x, y): return abs(sx - x) < 12 and abs(sy - y) < 8 print(touches(10, -76, 0, -80)) print(touches(30, -80, 0, -80)) ``` :::keep-together **What does it print?** ☐ True, then False ☐ True, then True ☐ False, then True ☐ False, then False My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** True, then False. The first star is 10 across and 4 up from the paddle: both are close enough (under 12 and under 8). The second is 30 across, too far. ::: ## Run Run the program in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Investigate ```python import random class Star: def __init__(self, x): self.x = x self.y = 100 self.speed = random.randint(5, 15) / 10 def move(self): self.y -= self.speed if self.y < -100: self.restart() def touches(self, x, y): return abs(self.x - x) < 12 and abs(self.y - y) < 8 def restart(self): self.y = 100 self.x = random.randint(-90, 90) def draw(self): screen.fillRound(self.x, self.y, 8, 8, "rgb(255,210,0)") def pressed(key): return hasattr(keyboard, key) and keyboard[key] != 0 def init(): global stars, px, score stars = [] for i in range(4): stars.append(Star(-60 + i * 40)) px = 0 score = 0 def update(): global px, score if pressed("LEFT"): px -= 2 if pressed("RIGHT"): px += 2 for star in stars: star.move() if star.touches(px, -80): score += 1 star.restart() def draw(): screen.clear("rgb(10,10,40)") for star in stars: star.draw() screen.fillRect(px, -80, 24, 6, "rgb(100,200,255)") screen.drawText("Score: " + str(score), 0, 88, 10, "#FFF") ``` :::keep-together ### Close enough **Why does touches() use and, not or?** ☐ A star must be close across and close up and down at the same time to touch ☐ It makes no difference ☐ and is faster than or ☐ or would never be true ::: :::teacher-note **Answer:** A star must be close across and close up and down at the same time to touch With or, a star anywhere in the same column (close across, far above) would count as a catch. Touching needs both distances small. ::: :::keep-together ### Why restart? **What would happen without star.restart() after score += 1?** ☐ Nothing would change ☐ The star scores once and disappears ☐ The star stays on the paddle and scores a point every frame ☐ The game stops with an error ::: :::teacher-note **Answer:** The star stays on the paddle and scores a point every frame The star would still be touching the paddle next frame, so the score would jump by 60 a second. restart() moves it back to the top. ::: :::keep-together ### Spot the bug **The score never goes past 1, however many stars you catch. Click the line that is wrong.** ``` 1 def init(): 2 global score 3 score = 0 4 5 def update(): 6 global score 7 for star in stars: 8 star.move() 9 if star.touches(px, -80): 10 score = 1 11 star.restart() ``` Line: {{field-15}} Why is it wrong? {{lines-2}} ::: :::teacher-note **Answer:** line 10 score = 1 sets the score to 1 every time. score += 1 adds one to what it was. ::: :::typical ## Modify **Lives.** Give the player **3 lives**: a star that reaches the bottom takes one. At 0 lives, stop the game and show **GAME OVER**. **Play again.** After GAME OVER, pressing **Space** starts a new game. The game on this page has both changes. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} :::teacher-note **One possible solution.** Other correct programs are fine; check that the program runs and does what the task asks. **Lives:** ```python import random class Star: def __init__(self, x): self.x = x self.y = 100 self.speed = random.randint(5, 15) / 10 def move(self): self.y -= self.speed def touches(self, x, y): return abs(self.x - x) < 12 and abs(self.y - y) < 8 def restart(self): self.y = 100 self.x = random.randint(-90, 90) def draw(self): screen.fillRound(self.x, self.y, 8, 8, "rgb(255,210,0)") def pressed(key): return hasattr(keyboard, key) and keyboard[key] != 0 def init(): global stars, px, score, lives lives = 3 stars = [] for i in range(4): stars.append(Star(-60 + i * 40)) px = 0 score = 0 def update(): global px, score, lives if lives == 0: return if pressed("LEFT"): px -= 2 if pressed("RIGHT"): px += 2 for star in stars: star.move() if star.touches(px, -80): score += 1 star.restart() elif star.y < -100: lives -= 1 star.restart() def draw(): screen.clear("rgb(10,10,40)") for star in stars: star.draw() screen.fillRect(px, -80, 24, 6, "rgb(100,200,255)") screen.drawText("Score: " + str(score) + " Lives: " + str(lives), 0, 88, 10, "#FFF") if lives == 0: screen.drawText("GAME OVER", 0, 0, 20, "rgb(255,100,100)") ``` **Play again:** ```python import random class Star: def __init__(self, x): self.x = x self.y = 100 self.speed = random.randint(5, 15) / 10 def move(self): self.y -= self.speed def touches(self, x, y): return abs(self.x - x) < 12 and abs(self.y - y) < 8 def restart(self): self.y = 100 self.x = random.randint(-90, 90) def draw(self): screen.fillRound(self.x, self.y, 8, 8, "rgb(255,210,0)") def pressed(key): return hasattr(keyboard, key) and keyboard[key] != 0 def init(): global stars, px, score, lives lives = 3 stars = [] for i in range(4): stars.append(Star(-60 + i * 40)) px = 0 score = 0 def update(): global px, score, lives if lives == 0: if pressed("SPACE"): init() return if pressed("LEFT"): px -= 2 if pressed("RIGHT"): px += 2 for star in stars: star.move() if star.touches(px, -80): score += 1 star.restart() elif star.y < -100: lives -= 1 star.restart() def draw(): screen.clear("rgb(10,10,40)") for star in stars: star.draw() screen.fillRect(px, -80, 24, 6, "rgb(100,200,255)") screen.drawText("Score: " + str(score) + " Lives: " + str(lives), 0, 88, 10, "#FFF") if lives == 0: screen.drawText("GAME OVER", 0, 0, 20, "rgb(255,100,100)") screen.drawText("Press SPACE to play again", 0, -20, 8, "#FFF") ``` ::: ::: ## Make: a power-up Add a **power-up**: a star that looks different and is worth more when caught (a gold star worth 5, a heart that gives back a life, a slow star that freezes the others...). It can be its own class, or a `Star` with an extra value. The game on this page has a fast gold star worth 5. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} :::teacher-note **One possible solution.** Other correct programs are fine; check that the program runs and does what the task asks. ```python import random class Star: def __init__(self, x): self.x = x self.y = 100 self.speed = random.randint(5, 15) / 10 def move(self): self.y -= self.speed if self.y < -100: self.restart() def touches(self, x, y): return abs(self.x - x) < 12 and abs(self.y - y) < 8 def restart(self): self.y = 100 self.x = random.randint(-90, 90) def draw(self): screen.fillRound(self.x, self.y, 8, 8, "rgb(255,210,0)") def pressed(key): return hasattr(keyboard, key) and keyboard[key] != 0 def init(): global stars, px, score stars = [] for i in range(4): stars.append(Star(-60 + i * 40)) gold = Star(0) gold.speed = 2.5 gold.gold = True stars.append(gold) px = 0 score = 0 def update(): global px, score if pressed("LEFT"): px -= 2 if pressed("RIGHT"): px += 2 for star in stars: star.move() if star.touches(px, -80): if hasattr(star, "gold"): score += 5 else: score += 1 star.restart() def draw(): screen.clear("rgb(10,10,40)") for star in stars: star.draw() screen.fillRect(px, -80, 24, 6, "rgb(100,200,255)") screen.drawText("Score: " + str(score), 0, 88, 10, "#FFF") ``` ::: :::wider ## Where this leads You have now built a whole game in a real engine: a loop, input, objects, collisions and a score. Next: draw your own sprites, add sound, and share it. ::: ## Exit ticket :::keep-together **Why does a caught star call restart()?** {{lines-3}} ::: :::teacher-note **Answer:** Otherwise it is still touching the paddle next frame and scores again, 60 times a second. :::