我正在使用要在网格上使用的矩形选择工具制作 HTML5 网格。它进展顺利，除非当我尝试使用矩形选择工具时，我的网格消失了。我希望网格留在画布上。
到目前为止，这是我的代码（如果您对此进行测试，您可能会更好地理解我的问题），
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<script type='text/javascript' src='http://code.jquery.com/jquery-1.7.1.js'></script>
<style type='text/css'>
*
{
margin: 0; padding: 0;
}
html, body
{
height: 100%; width: 100%;
}
canvas
{
display: block;
}
</style>
<script type='text/javascript'>//<![CDATA[
$(window).load(function(){
$(document).ready(function () {
function renderGrid(x_size,y_size, color)
{
var canvas = $("#myCanvas").get(0);
var context = canvas.getContext("2d");
context.save();
context.lineWidth = 0.5;
context.strokeStyle = color;
// horizontal grid lines
for(var i = 0; i <= canvas.height; i = i + x_size)
{
context.beginPath();
context.moveTo(0, i);
context.lineTo(canvas.width, i);
context.closePath();
context.stroke();
}
// vertical grid lines
for(var j = 0; j <= canvas.width; j = j + y_size)
{
context.beginPath();
context.moveTo(j, 0);
context.lineTo(j, canvas.height);
context.closePath();
context.stroke();
}
context.restore();
}
renderGrid(10,15, "gray");
});
});//]]>
</script>
</head>
<body>
<div style="height:480px;width:640px;border:1px solid #ccc;font:16px/26px Georgia, Garamond, Serif;overflow:auto;">
<canvas id="myCanvas" width="800" height="800" style="border:0px solid #000000;">
Your browser does not support the HTML5 canvas tag.
</canvas>
</div>
<script>
// Keep everything in anonymous function, called on window load.
if(window.addEventListener) {
window.addEventListener('load', function () {
var canvas, context;
// The active tool instance.
var tool;
var tool_default = 'rect';
function init () {
// Find the canvas element.
canvas = document.getElementById('myCanvas');
if (!canvas) {
alert('Error: I cannot find the canvas element!');
return;
}
if (!canvas.getContext) {
alert('Error: no canvas.getContext!');
return;
}
// Get the 2D canvas context.
context = canvas.getContext('2d');
if (!context) {
alert('Error: failed to getContext!');
return;
}
// Activate the default tool.
if (tools[tool_default]) {
tool = new tools[tool_default]();
}
// Attach the mousedown, mousemove and mouseup event listeners.
canvas.addEventListener('mousedown', ev_canvas, false);
canvas.addEventListener('mousemove', ev_canvas, false);
canvas.addEventListener('mouseup', ev_canvas, false);
}
// The general-purpose event handler. This function just determines the mouse
// position relative to the canvas element.
function ev_canvas (ev) {
if (ev.layerX || ev.layerX == 0) { // Firefox
ev._x = ev.layerX;
ev._y = ev.layerY;
} else if (ev.offsetX || ev.offsetX == 0) { // Opera
ev._x = ev.offsetX;
ev._y = ev.offsetY;
}
// Call the event handler of the tool.
var func = tool[ev.type];
if (func) {
func(ev);
}
}
// The event handler for any changes made to the tool selector.
function ev_tool_change (ev) {
if (tools[this.value]) {
tool = new tools[this.value]();
}
}
// This object holds the implementation of each drawing tool.
var tools = {};
// The rectangle tool.
tools.rect = function () {
var tool = this;
this.started = false;
this.mousedown = function (ev) {
tool.started = true;
tool.x0 = ev._x;
tool.y0 = ev._y;
};
this.mousemove = function (ev) {
if (!tool.started) {
return;
}
var x = Math.min(ev._x, tool.x0),
y = Math.min(ev._y, tool.y0),
w = Math.abs(ev._x - tool.x0),
h = Math.abs(ev._y - tool.y0);
context.clearRect(0, 0, canvas.width, canvas.height);
if (!w || !h) {
return;
}
context.strokeRect(x, y, w, h);
};
this.mouseup = function (ev) {
if (tool.started) {
tool.mousemove(ev);
tool.started = false;
}
};
};
init();
}, false); }
</script>
</body>
</html>
谢谢，如果您需要更多解释，请告诉我。