Learn X in Y minutes

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// p5.js has two important functions to work with.

function setup() {
  // the setup function gets executed just once when the window is loaded
}
function draw() {
  // the draw function gets called every single frame
  // if the framerate is set to 30, it would get called 30 times every second
}

// the following code explains all features

function setup() {
  createCanvas(640, 480); // creates a new canvas element with 640px as width as 480px as height
  background(128); // sets the background color to rgb(128, 128, 128)
  // background('#aaf') // you can use hex codes and color names too
}

function draw() {
  background('#f2f2fc'); // usually, you call `background` in draw to clear the screen
  // creates an ellipse at 10px from the top and 10px from the left, with width and height 37
  ellipse(10, 10, 37, 37);
  // remember in p5.js the origin is at the top-left corner of the canvas

  if (mouseIsPressed) {
    // mouseIsPressed is a boolean variable that is true when the mouse is down, and false otherwise

    fill(0); // fill sets the fill color, which will stay until it is changed
  } else {
    fill(255, 255, 255, 240); // fill(a, b, c, d) sets the fill color to rgba(a, b, c, d)
  }

  ellipse(mouseX, mouseY, 80, 80);
  // mouseX and mouseY are the x and y position of the mouse, respectively
  // the above code creates and ellipse under the mouse, and fills it with white or black


  // some other 2d primitives (shapes) you can draw:
  rect(9, 3, 23, 26); // x, y, width, height
  noFill(); // sets the fill color to transparent
  triangle(100, 400, 130, 200, 200, 300); // x1, y1, x2, y2, x3, y3
  point(100, 300); // create a point at x, y
  // there are more, but they are more complex.
}

/** Bouncing balls animation
 * You can copy-paste this code into the online editor at
 * https://editor.p5js.org/
 */
class Ball {
  constructor(x, y, xvel, yvel, radius, col) {
    this.position = createVector(x, y); // create a p5.Vector object which stores the x and y
    this.velocity = createVector(xvel, yvel); // make a p5.Vector storing the velocity
    this.radius = radius;
    this.col = col; // p5 already uses the word color, so we use col instead
  }

  update() {
    this.position.add(this.velocity); // you can add vectors with p5.Vector.add(p5.Vector)
    if (this.position.x + this.radius > width) {
      // flip the direction the ball is going in if it touches the edge
      this.velocity.x *= -1;
    }
    if (this.position.x - this.radius < 0) {
      this.velocity.x *= -1;
    }
    if (this.position.y + this.radius > height) {
      this.velocity.y *= -1;
    }
    if (this.position.y - this.radius < 0) {
      this.velocity.y *= -1;
    }
  }

  render() {
    // you can figure out what this does by now
    fill(this.col);
    ellipse(this.position.x, this.position.y, this.radius);
  }
}

let numBalls = 23;
let balls = [];

function setup() {
  createCanvas(400, 400); // width, height
  for (let i = 0; i < numBalls; i++) {
    let r = random(255); // random number between 0 and 255
    let g = random(255);
    let b = random(255);

    balls.push(
      new Ball(
        random(30, width), // x position
        random(height), // y position
        random(-4, 4), // x velocity
        random(-4, 4), // y velocity
        random(4, 10), // radius
        color(r, g, b) // fill color for the ball
      )
    );
  }
}

function draw() {
  background(255);
  for (let ball of balls) {
    ball.update();
    ball.render();
  }
}

// So far, we have only seen the default rendering mode.
// This time, we will use the 'webgl' renderer

function setup() {
  createCanvas(400, 400, WEBGL); // width, height, rendering mode
}

function draw() {
  background(0);

  stroke('#000');
  fill('#aaf');

  // rotate around the x, y, and z axes by the frame count divided by 50
  rotateX(frameCount / 50);
  rotateY(frameCount / 50);
  rotateZ(frameCount / 50);
  // frameCount is a p5.js variable that stores the amount of frames that have passed

  box(50, 50, 50); // width, height, depth
}