In this lab, I followed the instruction from JavaScript30 and recreated the Fun with HTML5 Canvas activity. First off, I made the HTML, CSS, and JavaScript files. Secondly, the <html>, <head>, <body>, <meta>, and <title> tags were already inserted in the HTML file. Thirdly, I typed in <link rel="stylesheet" type="text/css" href="Lab_22.css"> inside the <head> tags to link the CSS file with my HTML file. Fourthly, I typed in <script src="Lab_22.js" type="text/javascript"></script> inside the <body> tags which linked my JavaScript file with my HTML file. Inside the <body> tags, I typed the heading for the lab which has my name, date, and lab number with <div id="heading"><h1>Lab 22</h1><h2>Wei Jian Zhen</h2><h3>12/24/2019</h3></div>. After that, I added the <canvas> tags so that the user can draw. Lastly, I made the copyright notice with <p> and <div> tags. For the CSS I did html {width: 100%; height: auto;} body {background-color: #00FFA8; min-width: 100%; min-height: 100%;} to give the webpage a background color and make the webpage responsive to screen size changes. #heading {text-align: center; font-size: 16px;} to center the heading of the lab. #copyright {font-size: 16px; font-family: Baskerville, "Palatino Linotype", Palatino, "Century Schoolbook L", "Times New Roman", "serif"; font-weight: normal; padding-left: 1%; padding-right: 1%;} to change the font of the copyright notice. #draw {width: 100%;height: auto;border: thin solid #000000;} to give size and color to the canvas. For the JavaScript, I put:
// JavaScript Document
const canvas = document.querySelector('#draw');
const ctx = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
ctx.strokeStyle = '#BADA55';
ctx.lineJoin = 'round';
ctx.lineCap = 'round';
ctx.lineWidth = 100;
// ctx.globalCompositeOperation = 'multiply';
let isDrawing = false;
let lastX = 0;
let lastY = 0;
let hue = 0;
let direction = true;
function draw(e) {
if (!isDrawing) return; // stop the fn from running when they are not moused down
console.log(e);
ctx.strokeStyle = `hsl(${hue}, 100%, 50%)`;
ctx.beginPath();
// start from
ctx.moveTo(lastX, lastY);
// go to
ctx.lineTo(e.offsetX, e.offsetY);
ctx.stroke();
[lastX, lastY] = [e.offsetX, e.offsetY];
hue++;
if (hue >= 360) {
hue = 0;
}
if (ctx.lineWidth >= 100 || ctx.lineWidth <= 1) {
direction = !direction;
}
if(direction) {
ctx.lineWidth++;
} else {
ctx.lineWidth--;
}
}
canvas.addEventListener('mousedown', (e) => {
isDrawing = true;
[lastX, lastY] = [e.offsetX, e.offsetY];
});
canvas.addEventListener('mousemove', draw);
canvas.addEventListener('mouseup', () => isDrawing = false);
canvas.addEventListener('mouseout', () => isDrawing = false);
This creates the circles that can be clicked and dragged across the canvas to draw. Knowing how to make drawable canvas is useful to a web designer in case they want to make a drawing app or website.
Link:
http://techteach.us/Web2020/ZWeiJian/WCP/Labs/Lab_22/Lab_22.html
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