演示html5 canvas鼠标事件，获取canvas对象上的鼠标坐标，演示键盘事件通过键盘控制canvas上对象移动。
canvas对象支持所有的javascript的鼠标事件，包括鼠标点击(mouseclick), 鼠标按下(mouse down), 鼠标抬起(mouse up),鼠标移动( mouse move)对canvas添加鼠标事件方式有两种，一种方式是通过api来完成：
复制代码代码如下:
// mouse event
canvas.addeventlistener("mousedown",domousedown,false);
canvas.addeventlistener('mousemove', domousemove,false);
canvas.addeventlistener('mouseup', domouseup, false);
另外一种方式在javascript中称为反模式：
复制代码代码如下:
canvas.onmousedown = function(e){
}
canvas.onmouseup = function(e){
}
canvas.onmousemove = function(e){
}
获取鼠标在canvas对象上坐标：
由于canvas上鼠标事件中不能直接获取鼠标在canvas的坐标，所获取的都是基于整个
屏幕的坐标。所以通过鼠标事件e.pagex与e.pagey来获取鼠标位置，然后通过
canvas. getboundingclientrect()来获取canvas对象相对屏幕的相对位置，通过计算
得到鼠标在canvas的坐标，代码如下：
复制代码代码如下:
function getpointoncanvas(canvas, x, y) {
var bbox =canvas.getboundingclientrect();
return { x: x- bbox.left *(canvas.width / bbox.width),
y:y - bbox.top * (canvas.height / bbox.height)
};
}
键盘事件：
html5 canvas本身不支持键盘事件监听与获取，常用的有两种方法来解决这个问题：
一：通过windows对象来实现canvas键盘事件监听与处理
// key event - use window as object
window.addeventlistener('keydown', dokeydown,true);
二：通过在canvas对象上添加其它支持键盘事件的dom元素实现键盘事件支持
复制代码代码如下:
// key event - use dom element asobject
canvas.addeventlistener('keydown', dokeydown,true);
canvas.focus();
其中tabindex为html5 dom元素，支持键盘事件。
演示，一个可以根据键盘上下左右移动的矩形块:
一个完整的鼠标与键盘事件演示代码如下：
复制代码代码如下:
var tempcontext = null; // global variable 2d context
var started = false;
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;
if (!canvas.getcontext) {
console.log("canvas not supported. please install a html5 compatible browser.");
return;
}
// get 2d context of canvas and draw rectangel
tempcontext = canvas.getcontext("2d");
tempcontext.fillstyle="blue";
x = canvas.width/2;
y = canvas.height/2;
tempcontext.fillrect(x, y, 80, 40);
// key event - use dom element as object
canvas.addeventlistener('keydown', dokeydown, true);
canvas.focus();
// key event - use window as object
window.addeventlistener('keydown', dokeydown, true);
// mouse event
canvas.addeventlistener("mousedown", domousedown, false);
canvas.addeventlistener('mousemove', domousemove, false);
canvas.addeventlistener('mouseup', domouseup, false);
}
function getpointoncanvas(canvas, x, y) {
var bbox = canvas.getboundingclientrect();
return { x: x - bbox.left * (canvas.width / bbox.width),
y: y - bbox.top * (canvas.height / bbox.height)
};
}
function dokeydown(e) {
var keyid = e.keycode ? e.keycode :e.which;
if(keyid === 38 || keyid === 87) { // up arrow and w
clearcanvas();
y = y - 10;
tempcontext.fillrect(x, y, 80, 40);
e.preventdefault();
}
if(keyid === 39 || keyid === 68) { // right arrow and d
clearcanvas();
x = x + 10;
tempcontext.fillrect(x, y, 80, 40);
e.preventdefault();
}
if(keyid === 40 || keyid === 83) { // down arrow and s
clearcanvas();
y = y + 10;
tempcontext.fillrect(x, y, 80, 40);
e.preventdefault();
}
if(keyid === 37 || keyid === 65) { // left arrow and 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 canvas = event.target;
var loc = getpointoncanvas(canvas, x, y);
console.log("mouse down at point( x:" + loc.x + ", y:" + loc.y + ")");
tempcontext.beginpath();
tempcontext.moveto(loc.x, loc.y);
started = true;
}
function domousemove(event) {
var x = event.pagex;
var y = event.pagey;
var canvas = event.target;
var loc = getpointoncanvas(canvas, x, y);
if (started) {
tempcontext.lineto(loc.x, loc.y);
tempcontext.stroke();
}
}
function domouseup(event) {
console.log("mouse up now");
if (started) {
domousemove(event);
started = false;
}
}
html部分：
复制代码代码如下:
html canvas event demo - by gloomy fish
press w, a, s, d keys to move
