I'm working on a canvas javascript where with the mousemove event you can erase the background...
Now i'm trying to get the same experience for touchscreens (mobile). How can I give my code the mousemove and touchmove event at the same time?
(function() {
// Creates a new canvas element and appends it as a child
// to the parent element, and returns the reference to
// the newly created canvas element
function createCanvas(parent, width, height) {
var canvas = {};
canvas.node = document.createElement('canvas');
canvas.context = canvas.node.getContext('2d');
canvas.node.width = width || 100;
canvas.node.height = height || 100;
parent.appendChild(canvas.node);
return canvas;
}
function init(container, width, height, fillColor) {
var canvas = createCanvas(container, width, height);
var ctx = canvas.context;
// define a custom fillCircle method
ctx.fillCircle = function(x, y, radius, fillColor) {
/*this.fillStyle = fillColor;
this.beginPath();
this.moveTo(x, y);
this.arc(x, y, radius, 0, Math.PI * 2, false);
this.fill();*/
var radgrad = ctx.createRadialGradient(x, y, 0, x, y, radius);
radgrad.addColorStop(0, 'rgba(255,0,0,1)');
radgrad.addColorStop(0.8, 'rgba(255,0,0,.9)');
radgrad.addColorStop(1, 'rgba(255,0,0,0)');
// draw shape
ctx.fillStyle = radgrad;
ctx.fillRect(x - radius, y - radius, x + radius, y + radius);
};
ctx.clearTo = function(fillColor) {
ctx.fillStyle = fillColor;
ctx.fillRect(0, 1, width, height);
};
ctx.clearTo(fillColor || "#ddd");
// bind mouse events
canvas.node.onmousemove = function(e) {
if (!canvas.isDrawing) {
return;
}
var x = e.pageX - this.offsetLeft;
var y = e.pageY - this.offsetTop;
var radius = 100; // or whatever
var fillColor = '#ff0000';
ctx.globalCompositeOperation = 'destination-out';
ctx.fillCircle(x, y, radius, fillColor);
};
canvas.node.onmouseenter = function(e) {
canvas.isDrawing = true;
};
}
var container = document.getElementById('canvas');
init(container, 5000, 3000, '#f8fa58');
})();body {
margin-left: -10vw;
margin-top: -30vh;
background: url(https://i-d-images.vice.com/images/articles/meta/2014/10/21/untitled-article-1413860640.jpg?crop=1xw:0.44513137557959814xh;0xw,0.14219474497681608xh&resize=2000:*&output-format=image/jpeg&output-quality=75) no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
#canvas {
z-index: -1;
top: 2vh;
left: -10vw;
width: 110vw;
height: 130vh;
overflow: hidden;
}<div id="back"></div>
<div id="canvas"></div>You can use the same event handler, but inside, you'll have to process the event differently, because there is no clientX nor clientY property on touch[XXX] events.
Touch events can be multi-touch, so they do hold an array of touches, which have these coordinate properties.
IMO a cleaner way would be to split your event handler in two different phases : one to extract the event's coordinates, and one to do something with these coords.
(function() {
// a little verbose but...
function handleMousemove(event){
var x = event.clientX;
var y = event.clientY;
draw(x, y);
}
function handleTouchmove(event){
event.preventDefault(); // we don't want to scroll
var touch = event.touches[0];
var x = touch.clientX;
var y = touch.clientY;
draw(x, y);
}
// this one can be shared by both touch and move events
function activateDrawing(event){
event.preventDefault();
canvas.isDrawing = true;
}
function draw(eventX, eventY){
var x = eventX - canvas.node.offsetLeft;
var y = eventY - canvas.node.offsetTop;
if (!canvas.isDrawing) {
return;
}
var radius = 100; // or whatever
var fillColor = '#ff0000';
ctx.globalCompositeOperation = 'destination-out';
ctx.fillCircle(x, y, radius, fillColor);
}
function createCanvas(parent, width, height) {
var canvas = {};
canvas.node = document.createElement('canvas');
canvas.context = canvas.node.getContext('2d');
canvas.node.width = width || 100;
canvas.node.height = height || 100;
parent.appendChild(canvas.node);
return canvas;
}
var canvas, ctx; // got it out to avoid nesting too deeply my handlers;
function init(container, width, height, fillColor) {
canvas = createCanvas(container, width, height);
ctx = canvas.context;
// define a custom fillCircle method
ctx.fillCircle = function(x, y, radius, fillColor) {
var radgrad = ctx.createRadialGradient(x, y, 0, x, y, radius);
radgrad.addColorStop(0, 'rgba(255,0,0,1)');
radgrad.addColorStop(0.8, 'rgba(255,0,0,.9)');
radgrad.addColorStop(1, 'rgba(255,0,0,0)');
// draw shape
ctx.fillStyle = radgrad;
ctx.fillRect(x - radius, y - radius, x + radius, y + radius);
};
ctx.clearTo = function(fillColor) {
ctx.fillStyle = fillColor;
ctx.fillRect(0, 1, width, height);
};
ctx.clearTo(fillColor || "#ddd");
// bind mouse events
canvas.node.onmousemove = throttle(handleMousemove);
canvas.node.ontouchmove = throttle(handleTouchmove);
canvas.node.onmouseenter =
canvas.node.ontouchstart = throttle(activateDrawing);
}
var container = document.getElementById('canvas');
init(container, 5000, 3000, '#f8fa58');
/* Bonus : throttle these events so they don't fire too often */
function throttle(callback) {
var active = false; // a simple flag
var evt; // to keep track of the last event
var handler = function(){ // fired only when screen has refreshed
active = false; // release our flag
callback(evt);
}
return function handleEvent(e) { // the actual event handler
evt = e; // save our event at each call
if (!active) { // only if we weren't already doing it
active = true; // raise the flag
requestAnimationFrame(handler); // wait for next screen refresh
};
}
}
})();body {
margin-left: -10vw;
margin-top: -30vh;
background: url(https://i-d-images.vice.com/images/articles/meta/2014/10/21/untitled-article-1413860640.jpg?crop=1xw:0.44513137557959814xh;0xw,0.14219474497681608xh&resize=2000:*&output-format=image/jpeg&output-quality=75) no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
#canvas {
z-index: -1;
top: 2vh;
left: -10vw;
width: 110vw;
height: 130vh;
overflow: hidden;
}<div id="back"></div>
<div id="canvas"></div>