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script.js
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script.js
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let output = document.getElementById('output-lines');
let screen = document.getElementById("canvas");
let ongoingTouches = [];
let presstimer = null;
function startup() {
screen.addEventListener("touchstart", handleStart, false);
screen.addEventListener("touchend", handleEnd, false);
screen.addEventListener("touchcancel", handleCancel, false);
screen.addEventListener("touchmove", handleMove, false);
}
function handleStart(evt) {
evt.preventDefault();
log("Touch.event: start");
let ctx = screen.getContext("2d");
let touches = evt.changedTouches;
for (let i = 0; i < touches.length; i++) {
// log("touchstart:" + i + "...");
ongoingTouches.push(copyTouch(touches[i]));
let color = colorForTouch(touches[i]);
ctx.beginPath();
ctx.arc(touches[i].pageX, touches[i].pageY, 4, 0, 2 * Math.PI, false); // a circle at the start
ctx.fillStyle = color;
ctx.fill();
// log("touchstart:" + i + ".");
}
presstimer = setTimeout(function() {
log("Long press detected");
}, 1000);
}
function handleEnd(evt) {
evt.preventDefault();
log("Touch.event: end");
let ctx = screen.getContext("2d");
let touches = evt.changedTouches;
for (let i = 0; i < touches.length; i++) {
let color = colorForTouch(touches[i]);
let idx = ongoingTouchIndexById(touches[i].identifier);
if (idx >= 0) {
ctx.lineWidth = 4;
ctx.fillStyle = color;
ctx.beginPath();
ctx.moveTo(ongoingTouches[idx].pageX, ongoingTouches[idx].pageY);
ctx.lineTo(touches[i].pageX, touches[i].pageY);
ctx.fillRect(touches[i].pageX - 4, touches[i].pageY - 4, 8, 8); // and a square at the end
ongoingTouches.splice(idx, 1); // remove it; we're done
} else {
log("Can't figure out which touch to end");
}
}
clearPressTimeout();
}
function handleCancel(evt) {
evt.preventDefault();
log("Touch.event: cancel");
let touches = evt.changedTouches;
for (let i = 0; i < touches.length; i++) {
let idx = ongoingTouchIndexById(touches[i].identifier);
ongoingTouches.splice(idx, 1); // remove it; we're done
}
}
function handleMove(evt) {
evt.preventDefault();
let ctx = screen.getContext("2d");
log("Touch.event: move");
let touches = evt.changedTouches;
for (let i = 0; i < touches.length; i++) {
let color = colorForTouch(touches[i]);
let idx = ongoingTouchIndexById(touches[i].identifier);
if (idx >= 0) {
log("Continuing touch " + idx);
ctx.beginPath();
log("ctx.moveTo(" + ongoingTouches[idx].pageX + ", " + ongoingTouches[idx].pageY + ");");
ctx.moveTo(ongoingTouches[idx].pageX, ongoingTouches[idx].pageY);
log("ctx.lineTo(" + touches[i].pageX + ", " + touches[i].pageY + ");");
ctx.lineTo(touches[i].pageX, touches[i].pageY);
ctx.lineWidth = 4;
ctx.strokeStyle = color;
ctx.stroke();
ongoingTouches.splice(idx, 1, copyTouch(touches[i])); // swap in the new touch record
log(".");
} else {
log("Can't figure out which touch to continue");
}
clearPressTimeout();
}
}
function colorForTouch(touch) {
let r = touch.identifier % 16;
let g = Math.floor(touch.identifier / 3) % 16;
let b = Math.floor(touch.identifier / 7) % 16;
r = r.toString(16); // make it a hex digit
g = g.toString(16); // make it a hex digit
b = b.toString(16); // make it a hex digit
let color = "#" + r + g + b;
log("Color for touch with identifier " + touch.identifier + ": " + color);
return color;
}
function copyTouch({ identifier, pageX, pageY }) {
return { identifier, pageX, pageY };
}
function ongoingTouchIndexById(idToFind) {
for (let i = 0; i < ongoingTouches.length; i++) {
let id = ongoingTouches[i].identifier;
if (id == idToFind) {
return i;
}
}
return -1; // Not found
}
function clearPressTimeout(){
if (presstimer !== null) {
clearTimeout(presstimer);
presstimer = null;
}
}
function log(msg) {
output.innerHTML += msg + "<br>";
}
document.addEventListener("DOMContentLoaded", startup);