1. Detecting collisions Susan Ibach | Technical Evangelist
Sage Franch | Microsoft Student Partner

2. At the moment nothing happens when our hero hits an obstacle

3. How do we detect collisions between objects?
Pseudo code:
(the robot runs into an obstacle)
Remove a life from the game.
Sprite objects have a built-in collision detector!
Why not “if robot->overlaps with(obstacle)”? -> scope of robot.
Don’t do anything. (Just keep playing!)
Needs to be checked “on every frame”.

4. But there’s a catch!
Remember…sprite objects are rectangular! If the RECTANGLES overlap, then the sprites overlap.
Overlap?
Overlap?
No!
Yes!

5. Using “overlaps with”

6. Why am I losing multiple lives when I hit an obstacle?
Remember we are checking to see if we overlap on EVERY frame
Frame 1
Obstacle and hero overlap
Remove 1 life
Frame 2
Obstacle and hero overlap
Remove 1 life

7. Think like a coder…

8. Your challenge
Add code to remove a life if the hero hits an obstacle

9. Congratulations!
You’re getting close!

10. Vocabulary and concepts
Pseudo code: Literally, “fake” code, used to sketch out ideas in code without paying attention to the syntax.
Sprite: a 2-D image or animation that is integrated into a larger scene.
Collision detection: In TouchDevelop, a sprite is always a rectangle. Often, much of the rectangle is transparent. Two sprites collide when their rectangles overlap.
“overlaps with”: A function on a sprite used to detect a collision with another sprite. E.g. obstacle->overlaps with(hero). This function should be checked on every frame.