1. Intro CS – Screens and Variables
Lesson Plan 9

2. Goals Using sprites as full screens (Start screen, Game over)
Using layering to control ordering of screens
Using full screen sprites to create moving backgrounds
Using global and sprite level variables – when and why for each

3. Objectives
Students are introduced to the topic and given examples of full screen sprites for start/end screens, and for animated backgrounds; also examples of global and sprite level variables
Students are given real problems to code and solve for practice
Results are demonstrated through demos of running code and displayed results

4. Pre Requisites
Basic Understanding of Scratch, Sprites, Animation, Costumes, and Variables

5. Materials Slides with examples (or present on whiteboard)
PCs with development environments installed (this includes moving backgrounds that are pre-installed)

6. Lesson Description
Introduce full screen sprites, positioning, animating them
Review variables – used to track information that may change due to user input, hit detection, time, etc. Discusses when to use variables, how to use them, and what are their benefits and drawbacks (variables at sprite and global level)
Examples/demos – get scrolling background working in class
Students practice and extend problem to their own wishes
Students present their solutions, typically F2F with the instructor(s) at their desk
Students analyze their and others’ solutions for bugs
Won’t do Breakout game, instead give them time to work on their Galaga Projects.

7. Lesson Procedure
Review previous lessons: Repeat loops, Animation, Costumes, Hit Detection
In class examples:
Full screen sprite with layered button (click button to start)
Full screen sprites to animate background horizontally/vertically
Examples of global and local variables
Give exercises for in class practice
Walk the room answering questions, looking over the shoulder, asking questions, etc.
Won’t do Breakout game, instead give them time to work on their Galaga Projects.

8. Closure/Conclusion Discussion Summary
How do you add Start and Game over screens to your Galaga game?
What kind of scrolling background will you use?
How would you use global and local variables in your Galaga game?
Summary
Using variables to track app state and animation of backgrounds
Sprite vs. global variables
Ask questions on what is confusing or needs more time/practice

9. Animated Backgrounds and Scoped Variables
Lesson Plan 9
Today we’re going to talk about start, end, scrolling screens, and variables that help manage state that will help you guys in your Galaga project.
But first off, discuss the quiz (too hard, too easy? Everyone had enough time? Was everyone prepared?)
Secondly discuss what we learned last lesson – hit detection and broadcasting. Did anyone have trouble? What did a lot of you notice? Some people had trouble with the Done (variable) equals True statement, what do you guys think we had that for – to check for the state of the program (if the AngryShark had hit something).

10. 3 Concepts Today Needed for your Galaga projects Moving Backgrounds
Screens and Broadcasting
Variable Scoping

11. Backgrounds What have we done so far with backgrounds?
Backgrounds are static (can’t move) in BYOB
We can change them whenever we want using the two following blocks :
What else might we want to do?
What if we wanted a scrolling background in our Galaga game?
What if we wanted to create a Start or Game over screen?
Make sure everyone understands how to import and change a background, should be review.
How could we create a scrolling background in our game?
Paper demo: one piece of paper with a design how can we make it seem like it’s scrolling forever.
Hints: what does a treadmill do?
So how can we translate this to Scratch?

12. Moving Backgrounds?

13. Background in Galaga

14. Paper Prototype Partner up Get out some paper
Try to recreate either Fred’s or Galaga’s background as a quick mockup / prototype
How would you solve this in Snap?

15. Full Screen Sprites
Background images can also be used as regular Sprites - these are known as full screen sprites.
By using backgrounds as Sprites we can control:
Position
Animation/movement (tip: glide block will allow for smooth background movement)
Layering (tip: be careful of layering, make sure what you want to show is layered on top at the correct time; layering can be used to control ordering of screens)
Demo scrolling background
Full screen sprites will allow you to create moving backgrounds, think about Mario and Galaga space bgs.

16. The Pseudo code & Math Start BG1 fully on screen (at 0,0)
Start BG2 fully on screen (above at 0,360)
Move both down at same time
When BG1 goes off the bottom of the screen (0,-360), move it back to the middle
When BG2 goes to the center of the screen (0,0), move it back to the top

17. UPDATE
In the gear menu in Snap, turn on the Prefer smooth animations checkbox
Also, if you get a gap, create 2 variables and try this:
On each sprite
Stage

18. Screens and Broadcasting

19. Start Screen State

20. Play Button
Similar to everything else in Scratch, the Play Button will also be a Sprite, however it’s more of an object than a character.
Demo Play Button
Next thing we want to discuss is how to start your game by pressing a Play Button.
How do we think this might be accomplished?

21. Variable Scoping

22. Global vs. Sprite Variables
What is a Global variable?
Variable for all sprites
Example: In our past projects we have used a single variable for speed or step size.
What is a Sprite variable (also known as local variable)?
Variable for a single sprite
Example: If you want to make the dive directions for your enemy ships in Galaga different or anything else that is specific to a single sprite.
What else could we use global and sprite variables for?

23. Global vs. Sprite Variables – Used in Broadcasting
Scratch cannot limit where a Broadcast can go
Work around for this is to use a global variable and private/local/sprite variable for each sprite:
We discussed Global and Sprite Variables in the last Broadcasting lecture and it was also the Bonus question for your quizzes, does anyone remember what the difference between a Global and Sprite Variable are? How did it help Broadcasting?

24. Daily project
By the end of class: Add a scrolling background to your project
Extra: add a Start screen and button to your project
Show me "for this sprite only" variables and how they work

25. Summary Discussion Summary
How do you add Start and Game over screens to your Galaga game?
What kind of scrolling background will you use?
How would you use global and local variables in your Galaga game?
Summary
Using variables to track app state and animation of backgrounds
Sprite vs. global variables