Intro CS – Screens and Variables Lesson Plan 9

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

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

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

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

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

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.

Closure/Conclusion  Discussion  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

Animated Backgrounds and Scoped Variables Lesson Plan 9

3 Concepts Today 0 Needed for your Galaga projects 0 Moving Backgrounds 0 Screens and Broadcasting 0 Variable Scoping

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?

Moving Backgrounds?

Background in Galaga

Paper Prototype 0 Partner up 0 Get out some paper 0 Try to recreate either Fred’s or Galaga’s background as a quick mockup / prototype 0 How would you solve this in BYOB?

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

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

UPDATE 0 In the gear menu in Snap, turn on the Prefer smooth animations checkbox 0 Also, if you get a gap, create 2 variables and try this: Stage On each sprite

Screens and Broadcasting

Start Screen State

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

Variable Scoping

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.

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:

Daily project  By the end of class: Add a scrolling background to your project  Extra: add a Start screen and button to your project

Summary  Discussion  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