var tempContext = null; // konteks 2d pembolehubah global
var bermula = palsu;
var mText_canvas = null;
var x = 0, y =0;
window.add
window.onload = function() {
var canvas = document.getElementById("event_canvas");
console.log(canvas.parentNode.clientWidth);
canvas.width = canvas.parentNode.clientWidth;
canvas.height = canvas.parentNode.clientHeight;
jika (!canvas.getContext) {
console.log("Kanvas tidak disokong. Sila pasang penyemak imbas yang serasi dengan HTML5.");
kembali;
}
// dapatkan konteks 2D kanvas dan lukis segi empat tepat
tempContext = canvas.getContext("2d");
tempContext.fillStyle="blue";
x = canvas.width/2;
y = canvas.height/2;
tempContext.fillRect(x, y, 80, 40);
// acara utama - gunakan elemen DOM sebagai objek
canvas.addEventListener('keydown', doKeyDown, true);
canvas.focus();
// acara utama - gunakan tetingkap sebagai objek
window.addEventListener('keydown', doKeyDown, true);
// acara tetikus
canvas.addEventListener("mousedown", doMouseDown, false);
canvas.addEventListener('mousemove', doMouseMove, false);
canvas.addEventListener('mouseup', doMouseUp, false);
}
fungsi getPointOnCanvas(kanvas, x, y) {
var bbox = canvas.getBoundingClientRect();
kembali { x: x - bbox.left * (canvas.width / bbox.width),
y: y - bbox.top * (canvas.height / bbox.height)
};
}
fungsi doKeyDown(e) {
var keyID = e.keyCode ? e.keyCode :e.which;
if(keyID === 38 || keyID === 87) { // anak panah atas dan W
clearCanvas();
y = y - 10;
tempContext.fillRect(x, y, 80, 40);
e.preventDefault();
}
if(keyID === 39 || keyID === 68) { // anak panah kanan dan D
clearCanvas();
x = x 10;
tempContext.fillRect(x, y, 80, 40);
e.preventDefault();
}
if(keyID === 40 || keyID === 83) { // anak panah ke bawah dan S
clearCanvas();
y = y 10;
tempContext.fillRect(x, y, 80, 40);
e.preventDefault();
}
if(keyID === 37 || keyID === 65) { // anak panah kiri dan A
clearCanvas();
x = x - 10;
tempContext.fillRect(x, y, 80, 40);
e.preventDefault();
}
}
function clearCanvas() {
tempContext.clearRect(0, 0, 500, 500)
}
function doMouseDown(event) {
var x = event.pageX;
var y = event.pageY;
var kanvas = acara.sasaran;
var loc = getPointOnCanvas(kanvas, x, y);
console.log("tetikus turun pada titik( x:" loc.x ", y:" loc.y ")");
tempContext.beginPath();
tempContext.moveTo(loc.x, loc.y);
mula = benar;
}
fungsi doMouseMove(event) {
var x = event.pageX;
var y = event.pageY;
var kanvas = acara.sasaran;
var loc = getPointOnCanvas(kanvas, x, y);
jika (bermula) {
tempContext.lineTo(loc.x, loc.y);
tempContext.stroke();
}
}
fungsi doMouseUp(event) {
console.log("mouse up now");
jika (bermula) {
doMouseMove(event);
dimulakan = palsu;
}
}

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任>
如下: