--- title: "Space dodger" subtitle: "Arcade Foundations · Final challenge: Space dodger · Lesson 11" --- # Space dodger **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** Asteroids, Flappy Bird and every endless runner are the same game underneath: things come at you, you dodge, and the longer you last the better you score. :::teacher-note **In one sentence:** Students build a complete dodging game in three milestones, using a timer, random positions, velocity, overlaps, lives, score and the high score. **Students should be able to say:** I can make sprites appear on a timer and move them with velocity. I can make a hit cost exactly one life by destroying what was hit. I can combine timers, overlaps, lives and score into a game, and use the high score. **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 The ship can only move up and down: `moveSprite(ship, 0, 100)` gives it no speed across. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/b807e5156d67.png?v=c989dcc7a3408b12) :::keep-together **Where do the rocks fly across the screen?** ☐ From the left to the right ☐ All along the same line, through the middle ☐ They do not move ☐ At a different height each time My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** All along the same line. Every rock starts at (160, 60), so they all come through the middle, where the ship starts. ::: ## Run Run the program in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Investigate This is the working start of the game. Read it, and change numbers in the playground to test your answers. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/b807e5156d67.png?v=c989dcc7a3408b12) :::keep-together ### Who does what Match each block with its job. The timer in Python: ```python def on_update_interval(): global rock rock = sprites.create(img("""..."""), SpriteKind.enemy) rock.set_position(160, 60) rock.vx = -50 game.on_update_interval(1000, on_update_interval) ``` The timer becomes a `def`: a named job handed to the game, which runs it every second. Blocks write this for you. (Functions are the first lesson of Arcade advanced skills.) **Match each block with its job in the game.** A. starts each rock at the right edge B. lets the ship move up and down only C. moves each rock left, every frame D. makes a new rock every second {{columns 60% 40%}} {{rows 1}} | Part | Letter | |---|---| | `on game update every 1000 ms` | | | `set rock position to (160, 60)` | | | `set rock vx to -50` | | | `move ship with buttons, vx 0, vy 100` | | ::: :::teacher-note **Answer:** on game update every 1000 ms → D. makes a new rock every second; set rock position to (160, 60) → A. starts each rock at the right edge; set rock vx to -50 → C. moves each rock left, every frame; move ship with buttons, vx 0, vy 100 → B. lets the ship move up and down only The timer makes the rocks, the position says where each starts, and velocity keeps it moving. The ship's 0 across means left and right do nothing. ::: :::keep-together ### How long to react? **A rock starts at x 160 and moves 50 pixels left every second. The ship is at x 20. How many seconds does the rock take to reach the ship?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 2.8 The rock travels 160 - 20 = 140 pixels at 50 pixels a second: 140 / 50 = 2.8 seconds. A bigger speed gives the player less time. ::: :::keep-together ### Where do the rocks go? **Ava plays for a minute. A rock goes past the ship and off the left edge. What happens to it?** ☐ It turns around ☐ It keeps flying left forever, off the screen, and the game keeps track of it ☐ It comes back on the right ☐ It is removed when it leaves the screen ::: :::teacher-note **Answer:** It keeps flying left forever, off the screen, and the game keeps track of it Nothing destroys it, so it keeps moving off the screen. After a few minutes there are hundreds of rocks nobody can see. Milestone 1 fixes this. ::: :::keep-together ### Leo's game ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/4157f57f428e.png?v=ed56f0b2eaaa871f) **Leo adds an overlap event for Player and Enemy that takes away a life, but forgets to destroy the rock. He starts with 3 lives. A rock touches his ship. What happens?** ☐ He loses all 3 lives almost at once and the game ends ☐ He loses 1 life and the rock flies on ☐ He loses 1 life and the rock disappears ☐ Nothing: the rock must be destroyed first ::: :::teacher-note **Answer:** He loses all 3 lives almost at once and the game ends The overlap event runs every frame while the rock still touches the ship, about 30 times a second, so 3 lives go in a tenth of a second. Destroy the rock in the event. ::: :::typical ## Milestone 1: rocks from anywhere **Behind the code:** **set rock auto destroy on** (Sprites, the **set flag** block) tells the engine to remove the sprite as soon as it leaves the screen. Without it, every rock that missed the ship keeps flying forever. 1. Start each rock at a **random height**, from 10 to 110. 2. Set each rock to **auto destroy**. 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. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/4d2551a6d19f.png?v=67875a37e794324b) ::: ::: :::typical ## Milestone 2: lives and a hit Give the player **3 lives**, and make a hit count: - When the ship touches a rock, **destroy the rock** and **lose a life**. - At zero lives, the game ends by itself. 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. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/ee1f21f4b385.png?v=130e9d73d6b786d6) ::: ::: ## Make: Milestone 3: score and high score **Behind the code:** **high score** (in **Info**) is the best score so far in this browser. The game over screen shows it by itself; you can also use it in your blocks. Finish the game: - The score goes up by **1 every second** the player survives. - Use **high score** to show the player when they are beating their best (a new background colour, a splash, or your own idea). - Play three games. Does the game over screen show your best? 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. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/ba646a0e9097.png?v=46b513b25d3699b5) ::: :::wider ## Change a road crossing The same game turned on its side: cars drive across, and the chick scores by reaching the top. Make it yours. Ideas: faster cars as the score goes up, cars from both sides, a second lane of logs, or a short effect when a car hits (Sprites › Effects). Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} ::: ## Exit ticket :::keep-together **Why must the rock be destroyed inside the overlap event?** {{lines-3}} ::: :::teacher-note **Answer:** The overlap event runs every frame the two sprites touch. Destroying the rock makes it touch once, so a hit costs one life, not all of them. :::