Batch 2 - Class 23 - App Inventor Session 3

Attendance: Smiti, Muskaan, Aastha, Hriday, Kushaan, Tishyaa, Abhiram, Avy, Aryan, Rhea, Diya and Adit on Skype

Class Notes:

Drawing Shapes/Images on Canvas http://www.appinventor.org/Drawing

Drag a Canvas - set width to FillParent and height to some number
Coordinate system on canvas - Initialize the screen and draw a circle at various points
Draw a circle where the user touches
Draw a circle in center of screen

Build a game - Space Invaders http://appinventor.mit.edu/explore/ai2/space-invaders.html

Explain to kids what we will be creating. Invite ideas on "specifying" what we are creating, and what all should we have - both on design and on blocks/functionality

Design

Create a new project SpaceInvaders, and rename the screen to Space Invaders
Download these images to your computer http://appinventor.mit.edu/explore/sites/all/files/ai2tutorials/SpaceInvaders/rocket.png and http://appinventor.mit.edu/explore/sites/all/files/ai2tutorials/SpaceInvaders/saucer.png
Pull a Canvas from Drawing and Animation; set width/height; set background to black
Pull 2 ImageSprites and set them to rocket (set Y=230 - why?) and saucer; Pull a BallSprite - change paintcolor to desired color of bullet, and radius to 8
Pull out a Clock from Sensor - this will be used to move the saucer. Set TimerInterval to 3000
Put two Labels in a HorizontalArrangement - Set first to "Score" and second to "0" - the latter will be a score counter
Pull out a button which we will use to reset the game - call it "Reset"

Ask kids to check the above on Companion App

Functionality/Blocks

Discuss with kids on what events should each item on the design move.

The rocket should move, only horizontally, when we drag it with our finger. Ask kids to program this by pulling in the right event handler, and setting the right variable. Test
Bullet has complex behavior

It should be invisible before being shot from the rocket - Initially set it to invisible
It should move upwards after being shot - triggered by touching the RocketSprite (Note 90 is the value to get the bullet to head up; speed is pixels/sec so set it to 5)
On colliding with the saucer, it should again become invisible and score should increase - ask kids to identify the event handler (collide - note that it can't collide with anything else)
Test - what are the remaining issues
When bullet reaches the top - it should become invisibleWhen you touch the rocket, the bullet should return to the rocket and then shoot up - let kids discover how to position the bullet at the rocket)

Test the game - the basic game should work now

Program the reset button

Should be simple - just reset the score when reset button is clicked

Increasing the difficulty

Let kids discuss the problems and how they can improve the game

Since the saucer is stationary, you can keep hitting it now... so lets try to change position of saucer randomly after each hit
To make it even more difficult, let change position of saucer everytime the timer goes off

Customization Exercise

Let kids save this version and publish it. Now let them make other changes that they would like to make to the program - allow 10 minutes for discussion on what features they would like to add.

Homework: Think of how you can make the game more interesting, and implement some cool features