HTML5画布 - 在画布上拖动文本问题

时间:2011-02-16 14:28:04

标签: javascript html5 canvas

我想拖动位于Canvas上的文本,我找到了一个教程如何拖动一个Rectange但我无法在文本上实现它,这是下面的移动矩形的代码,可以帮助我实现一些它在文字上?

<!doctype html>
<html>
<head>
<meta charset="UTF-8" />
<title>Canvas Drag and Drop Test</title>
</head>
<body>
<section>

<div>
<canvas id="canvas" width="400" height="300">
This text is displayed if your browser does not support HTML5 Canvas.
</canvas>
</div>

<script type="text/javascript">

var canvas;
var ctx;
var x = 75;
var y = 50;
var dx = 5;
var dy = 3;
var WIDTH = 400;
var HEIGHT = 300;
var dragok = false;

function rect(x,y,w,h) {
 ctx.beginPath();
 ctx.rect(x,y,w,h);
 ctx.closePath();
 ctx.fill();
}

function clear() {
 ctx.clearRect(0, 0, WIDTH, HEIGHT);
}

function init() {
 canvas = document.getElementById("canvas");
 ctx = canvas.getContext("2d");
 return setInterval(draw, 10);
}

function draw() {
 clear();
 ctx.fillStyle = "#FAF7F8";
 rect(0,0,WIDTH,HEIGHT);
 ctx.fillStyle = "#444444";
 rect(x - 15, y - 15, 30, 30);
}

function myMove(e){
 if (dragok){
  x = e.pageX - canvas.offsetLeft;
  y = e.pageY - canvas.offsetTop;
 }
}

function myDown(e){
 if (e.pageX < x + 15 + canvas.offsetLeft && e.pageX > x - 15 +
 canvas.offsetLeft && e.pageY < y + 15 + canvas.offsetTop &&
 e.pageY > y -15 + canvas.offsetTop){
  x = e.pageX - canvas.offsetLeft;
  y = e.pageY - canvas.offsetTop;
  dragok = true;
  canvas.onmousemove = myMove;
 }
}

function myUp(){
 dragok = false;
 canvas.onmousemove = null;
}

init();
canvas.onmousedown = myDown;
canvas.onmouseup = myUp;

</script>

</section>
</body>
</html>

Test

而且当我在HEAD标签中添加此代码时,它不起作用。为什么会这样?

1 个答案:

答案 0 :(得分:8)

基本示例 http://jsfiddle.net/h3BCq/1/

上传一个(保持rect函数,添加新文本函数,绘制文本的边界框) http://jsfiddle.net/h3BCq/2/

我绝对是在欺骗。我使用px的字体大小更容易抓住它的宽度。您可以使用em或点,但您只需要转换为像素即可获得估计的宽度。我基本上只删除了rect,并添加了filltext,并修改了检查以检查文本宽度。