The Basics of p5js¶

Quick Overview of Day

Draw primitive shapes in p5js. Explore storing color values.

Class Demo¶

p5js has a number of functions that get called automatically for you. The most important ones for now are setup(), draw(), keyTyped() and mousePressed().

Live code a demo that does the following:

displays a circle on the screen (talk about the coordinate plane)
update the location of the circle so that it goes wherever the mouse goes (mouseX and mouseY)
use console.log() to provide diagnostic messages (super useful when debugging your code)
make the circle start to move around the screen (global variables for x and y location, and x and y velocity; conditional statements to bounce when colliding with walls)
have the circle change to a random color every time it collides with a wall
whenever the mouse is pressed, choose new random values for x and y velocities
use a random image from the web instead of the circle (PImage)
if time/inclination allows, use the scroll wheel to change the size of the image moving around
clean up the draw() loop so that it calls other user-defined functions

To Remember¶

use keyTyped() instead of keyPressed() in keyTyped(), the key variable is case sensitive!
can return false; to override default behaviour of that key (like space key scrolling…)

p5js helpful variables¶

In addition to what we’ve already done, here’s a quick list of system variables that you will likely find useful. You may want to look up more information about these using the p5js.org reference.

width - Width (in pixels) of canvas
height - Height (in pixels) of canvas
frameCount - Number of frames processed
frameRate() - Rate that frames are processed (per second)
windowWidth - Width (in pixels) of entire screen
windowHeight - Height (in pixels) of entire screen
key - Most recent key pressed on the keyboard
keyCode - Numeric code for key pressed on keyboard
keyIsPressed - True or false? Is a key pressed?
mouseIsPressed - True or false? Is the mouse pressed?
mouseButton - Which button is pressed? Left, right, or center
mouseX - Current horizontal location of the mouse
mouseY - Current vertical location of the mouse

Your Turn¶

Create a sketch that makes the following happen:

displays an image of a character at some x and y location (save these in global variables)
make the character move according to WASD controls (keyIsDown will be your friend here…)

Start of Class Mini-Challenge¶

Create a sketch that makes the following happen:

when the user clicks on the sketch AND is holding down the r key, draw a rectangle there
when the user clicks on the sketch AND is holding down the e key, draw a circle there
when the user hits the “w” key, reset the sketch with a white background
when the user hits the “b” key, reset the sketch with a black background

You’ll want to look up the mouseClicked() function in the p5js.org reference.

Take it Further¶

see if you can use the up/down arrow keys to adjust the size of the rectangle and circle that your program draws
use some other key(s) to change the color used for the shapes

Note

If you want to use the right mouse button as an input for your sketch, you will want to disable the normal right mouse button behaviour of your browser. To do that, include the following in your setup() function: document.addEventListener("contextmenu", event => event.preventDefault()). If you are curious how this works, you’d need to look up arrow functions.

Another Mini-Challenge¶

Create a sketch to make the following happen:

when the mouse is on the left-hand side of your screen, rectangles should be drawn (on the left half of the screen). The rectangles should be various shades of grey.
when the mouse is on the right-hand side of the screen, circles should be drawn on the right side of the screen (in random colours).