MIT App Inventor

Lesson 4 – Drawing on a Canvas

AgendaDrawing on a Canvas

◦Events Touched Dragged

Algorithms◦Increment / decrement

CanvasGrid for animation and graphicsUses (x,y) coordinates to locate

objects

(0,0)

(0,400)

(300,0)

(300,400)

Canvas components

coordinates provided to event handlerIn this case the action is to Draw a Circle

on the same canvas◦ can have multiple canvas objects

Controlling ObjectsA separate canvas and sprite can be

used as a game controller.The value of draggedSprite is True

when the sprite is being dragged

Algorithms

Patterns

Increment◦Increase the value stored in a

variable

Decrement◦Decrease the value stored in a

variable

Lab 5 – Paint the Puppy

ObjectiveCreate an interactive drawing program.

◦Components Canvas

◦Concepts Responding to user input

Touched Dragged

◦Algorithms Increment / Decrement of variables