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# Space dodger
Arcade Foundations · Final challenge: Space dodger
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## Today
**We are learning to** build a complete game that uses everything so far. Steer a ship through rocks, keep your lives, and beat your high score.
- 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.
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## Why it matters
> 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.
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💬 Discussion
## Predict
**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
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✅ Check
## What happened?
* All along the same line. Every rock starts at (160, 60), so they all come through the middle, where the ship starts.
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✍️ Activity
## Run it
Open the lesson at this step and try it together.
[studio.learningwaypoints.com/tutorials/code/arcade/arcade-dodger/?full=step-2#step-2](https://studio.learningwaypoints.com/tutorials/code/arcade/arcade-dodger/?full=step-2#step-2)
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💬 Discussion
## Investigate
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💬 Discussion
## 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.)
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✅ Check
## Who does what
**Match each block with its job in the game.**
| | |
|---|---|
| `on game update every 1000 ms` | A. starts each rock at the right edge |
| `set rock position to (160, 60)` | B. lets the ship move up and down only |
| `set rock vx to -50` | C. moves each rock left, every frame |
| `move ship with buttons, vx 0, vy 100` | D. makes a new rock every second |
* 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
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✅ Check
## 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: 2.8
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✅ Check
## 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
* Answer: It keeps flying left forever, off the screen, and the game keeps track of it
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✅ Check
## Leo's game
**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
* Answer: He loses all 3 lives almost at once and the game ends
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✍️ Activity
## Plan the milestones (4 min)
On the board, list what the finished game needs: random rocks, lives, a hit, a score, a high score. Next to each, write the block or event that does it.
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✍️ Activity
## 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**.
[Open this step](https://studio.learningwaypoints.com/tutorials/code/arcade/arcade-dodger/?full=step-4#step-4)
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✍️ Activity
## 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.
[Open this step](https://studio.learningwaypoints.com/tutorials/code/arcade/arcade-dodger/?full=step-5#step-5)
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✍️ Activity
## 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?
[Open this step](https://studio.learningwaypoints.com/tutorials/code/arcade/arcade-dodger/?full=step-6#step-6)
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✍️ Activity
## 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).
[Open this step](https://studio.learningwaypoints.com/tutorials/code/arcade/arcade-dodger/?full=step-7#step-7)
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✍️ Activity
## High-score board (4 min)
Write your high score on the board. Swap games and suggest one change that makes the next pair's game fairer or harder.
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✅ Check
## Exit ticket
**Why must the rock be destroyed inside the overlap event?**
* 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.