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Collision Detection

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Problem Decomposition Returns!

  • How do we know when these circles are touching?
  • How does the distance help us determine a collision?
  • What functions would be useful to write here?
  • Top-Down, Bottom-Up!

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Problem Decomposition Returns!

You may remember that there are two strategies for doing this:

Top-Down: Describe the problem at a high level, then fill in the details later.

Bottom-Up: Focus on the smaller parts that you’re sure of, then build them together to get the big picture.

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Problem Decomposition Returns!

A retractable pole starts out 24 inches tall, and grows at a rate of 0.6in/sec. An elastic is tied to the top of the pole and anchored 200 inches from the base, forming a right triangle. Define functions that compute the height of the pole and the area of the triangle after a given number of seconds.

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Turn to Top Down, Bottom Up (Page 57) in your student workbook, and solve this word problem using any order you like!

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Problem Decomposition Returns!

Which strategy did you use? Top-Down or Bottom-Up?

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Did you start out with one, and then switch to another?

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Which was easier for you?

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Collision Detection

We already have a function that will tell us how close together two points are. What is that function called?

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Knowing how far apart our characters are is only the first step! We still need the computer to be asking: "Are they close enough to collide?"

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Collision Detection

  • Use the Design Recipe to write collide? (Page 58), which that takes in two coordinates (four numbers) of the player (px, py) and a character (cx, cy), and returns true if they are within 50 pixels of each other.
  • Fix the collide? function in your game file, and click Run!

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Collision Detection

You started by writing the distance function first, and then collide? Is this Top-Down or Bottom-Up decomposition?

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collide? function was easy to write, because we could re-use the distance function.

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Have we done anything like this before?

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