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canvas.html
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canvas.html
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<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport"
content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Air Pen</title>
<link href="normalize.css" rel="stylesheet" type="text/css">
<style>
html {
-webkit-box-sizing: border-box;
box-sizing: border-box;
-ms-touch-action: none;
touch-action: none;
}
body {
position: absolute;
width: 100%;
height: 100%;
background-color: grey;
display: flex;
justify-content: center;
}
.o-select-none {
user-select: none;
-webkit-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
}
.o-canvas-wrapper {
position: absolute;
width: 100%;
height: 100%;
}
#o-canvas {
position: absolute;
width: 100%;
height: 100%;
cursor: crosshair;
background-color: white;
}
.o-buttons-wrapper {
display: flex;
justify-content: space-between;
width: 100%;
position: absolute;
bottom: 0;
height: 40px;
}
.o-button {
width: 100px;
height: 100%;
}
</style>
</head>
<body>
<div class="o-canvas-wrapper">
<canvas class="o-select-none" id="o-canvas">Your browser needs to be updated!</canvas>
</div>
<div class="o-buttons-wrapper">
<button class="o-button" id="o-clear-button">Clear</button>
<button class="o-button" id="o-grid-button">Grid</button>
<button class="o-button" id="o-save-button">Save</button>
</div>
<script>
const CANVAS_SCALE = 2;
const canvas = document.querySelector('#o-canvas');
const clearButton = document.getElementById("o-clear-button");
const gridButton = document.getElementById("o-grid-button");
const saveButton = document.getElementById("o-save-button");
canvas.width = window.innerWidth * CANVAS_SCALE;
canvas.height = window.innerHeight * CANVAS_SCALE;
canvas.addEventListener('mousedown', start_drawing);
canvas.addEventListener('touchstart', start_drawing);
canvas.addEventListener('mousemove', draw);
canvas.addEventListener('touchmove', draw);
canvas.addEventListener('mouseup', stop_drawing);
canvas.addEventListener('mouseout', stop_drawing);
canvas.addEventListener('touchend', stop_drawing);
clearButton.addEventListener('click', clear_drawing);
gridButton.addEventListener('click', add_grid);
saveButton.addEventListener('click', save_drawing);
document.addEventListener('keydown', process_drawing);
const context = canvas.getContext('2d');
context.strokeStyle = 'black';
context.lineJoin = 'round';
context.lineCap = 'round';
context.lineWidth = 2 * CANVAS_SCALE;
// retrieve saved canvas from local storage
if (localStorage.getItem('saved-canvas')) {
savedCanvas = new Image();
savedCanvas.addEventListener("load", function () {
context.drawImage(savedCanvas, 0, 0);
});
savedCanvas.src = localStorage.getItem('saved-canvas');
}
class Pen {
/**
* @return {null}
*/
constructor() {
if (pen) {
return pen;
}
this.isOn = false;
this.x = 0;
this.y = 0;
this.hasGrid = false;
}
turn_on() {
this.isOn = true;
}
turn_off() {
this.isOn = false;
}
record_position(x, y) {
this.x = x;
this.y = y;
}
set_position(e) {
const x = e.pageX * CANVAS_SCALE;
const y = e.pageY * CANVAS_SCALE;
const force = (e.touches && e.touches[0] && e.touches[0]["force"]) || 0.1;
context.lineWidth = (Math.exp(1.2 * force) + 3) * CANVAS_SCALE;
this.record_position(x, y);
}
start_drawing(e) {
this.turn_on();
context.beginPath();
this.set_position(e);
context.moveTo(this.x, this.y);
}
draw(e) {
context.beginPath();
context.moveTo(this.x, this.y);
this.set_position(e);
context.lineTo(this.x, this.y);
context.stroke();
}
stop_drawing() {
this.turn_off();
}
}
let pen = null;
pen = new Pen();
function start_drawing(e) {
e.preventDefault();
pen.start_drawing(e);
}
function draw(e) {
e.preventDefault();
if (!pen.isOn) return;
pen.draw(e);
}
function stop_drawing(e) {
e.preventDefault();
pen.stop_drawing();
}
function clear_drawing() {
context.clearRect(0, 0, canvas.width, canvas.height);
pen.hasGrid = false;
}
function add_grid() {
if (pen.hasGrid) return;
context.strokeStyle = "#ccc";
context.lineWidth = CANVAS_SCALE;
for (let x = 0; x < canvas.width; x += 100 * CANVAS_SCALE) {
context.moveTo(x, 0);
context.lineTo(x, canvas.height);
}
for (let y = 0; y < canvas.height; y += 100 * CANVAS_SCALE) {
context.moveTo(0, y);
context.lineTo(canvas.width, y);
}
context.stroke();
pen.hasGrid = true;
context.strokeStyle = "black";
context.lineWidth = 2 * CANVAS_SCALE;
}
function save_drawing() {
localStorage.setItem('saved-canvas', canvas.toDataURL('image/png'));
window.location = canvas.toDataURL('image/png');
}
function process_drawing(event) {
if ((event.ctrlKey || event.metaKey) && event.key === "s") {
event.preventDefault();
save_drawing();
}
}
</script>
</body>
</html>