我在网上发现了许多教程，用于在HTML画布中拖放图像和形状。但它们似乎都旨在移动页面加载时在画布内生成的对象。我正在构建一个应用程序，让用户单击虚拟键盘上的按钮，然后单击画布以显示相应的数字或字符。这是我的代码：
<script type="text/javascript">
var mathCanvas = document.getElementById("matharea");
var ctx = mathCanvas.getContext("2d");
ctx.font="20px Arial";
var placementCallback = function(){}
mathCanvas.onselectstart = function(){return false;}
function insertOne(){placementCallback = function(x, y){ctx.fillText('1', x-6,y+6);}};
function insertTwo(){placementCallback = function(x, y){ctx.fillText('2', x-6,y+6);}};
function insertThree(){placementCallback = function(x, y){ctx.fillText('3', x-6,y+6);}};
mathCanvas.onclick = function(event){
placementCallback(event.offsetX, event.offsetY);
}
</script>
我删除了一些插入函数以使其更短（我的HTML中的按钮具有调用这些函数的onclick属性）。我需要能够选择放在屏幕上的字符并实现拖放和删除功能，但我想不出有办法在页面加载后放置在屏幕上的文本（I对Javascript来说还是个新手。我该怎么做？我不希望任何人给我代码来做这件事，但如果我能朝正确的方向努力，那就太好了。
答案 0 :(得分：0)
问题是canvas是立即模式。无论你把它放在画布上，它都会立即放在画布上。它不会让您能够以任何方式，形状或形式修改该值。
将其视为MS Paint（或您的OS'等效物）与Photoshop之间的区别 在PS中，您可以拥有可以移动和编辑的图层，当您决定完成图像时，您可以保存它并使所有数据变平。
当您在MS Paint中制作图像时，只要您单击或键入，您放置的那个东西就在那里，除非您擦除它，绘制它或绘制一个矩形，否则它不会移动/被编辑一个部分并移动整个矩形（包括你想要编辑的像素周围的像素）。
只需调用fillText就会在那一瞬间绘制单词，但不会记住它绘制的内容，它的位置，内容，文本与周围像素的差异等等。
因此，您的通用解决方案是您需要将文本转换为对象，然后将这些对象的一个方面（文本内容）绘制到屏幕上。
如果文本发生变化，您可以对对象进行更改并重新绘制（因为您的对象将存储其X和Y坐标，并且将使用其存储宽度值， context.measureText(textObj.text).width方法/属性），当您单击画布时，可以检查单击的坐标，如果这些坐标与文本对象的存储坐标相交，则可以在屏幕上修改其位置
在这方面，您应该查看那些处理在画布上拖动对象的示例 按钮点击应被视为 创建 其中一个对象的方式。
答案 1 :(得分：-1)
我知道这是很多代码...但我不想通过它..它是我很久以前建立的东西的一部分......只需复制并粘贴到html文件中......我希望它能满足您的需求：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.17/jquery-ui.min.js" type="text/javascript"></script>
<script src="http://jquery-ui.googlecode.com/svn/tags/latest/external/jquery.bgiframe-2.1.2.js" type="text/javascript"></script>
<script src="http://jquery-ui.googlecode.com/svn/tags/latest/ui/minified/i18n/jquery-ui-i18n.min.js" type="text/javascript"></script>
<script type="text/javascript" src="http://ajax.microsoft.com/ajax/jquery.validate/1.7/jquery.validate.min.js"></script>
<script>
;(function($) {
$.fn.insertAtCaret = function (myValue) {
return this.each(function() {
//IE support
if (document.selection) {
this.focus();
sel = document.selection.createRange();
sel.text = myValue;
this.focus();
} else if (this.selectionStart || this.selectionStart == '0') {
//MOZILLA / NETSCAPE support
var startPos = this.selectionStart;
var endPos = this.selectionEnd;
var scrollTop = this.scrollTop;
this.value = this.value.substring(0, startPos)+ myValue+ this.value.substring(endPos,this.value.length);
this.focus();
this.selectionStart = startPos + myValue.length;
this.selectionEnd = startPos + myValue.length;
this.scrollTop = scrollTop;
} else {
this.value += myValue;
this.focus();
}
});
};
})(jQuery);
$(function go_prev() {
//When you click on a link with class of poplight and the href starts with a #
$('a.poplight[href^=#]').click(function() {
var popID = $(this).attr('rel'); //Get Popup Name
var popURL = $(this).attr('href'); //Get Popup href to define size
//Pull Query & Variables from href URL
var query= popURL.split('?');
var dim= query[1].split('&');
var popWidth = dim[0].split('=')[1]; //Gets the first query string value
//Fade in the Popup and add close button
$('#' + popID).fadeIn().css({ 'width': Number( popWidth ) }).prepend('<a href="#" class="close"><img src="close_pop.png" class="btn_close" title="Close Window" alt="Close" /></a>');
//Define margin for center alignment (vertical horizontal) - we add 80px to the height/width to accomodate for the padding and border width defined in the css
var popMargTop = ($('#' + popID).height() + 90) / 2;
var popMargLeft = ($('#' + popID).width() + 80) / 2;
//Apply Margin to Popup
$('#' + popID).css({
'top' : 10,
'margin-left' : -popMargLeft
});
//Fade in Background
$('body').append('<div id="fade"></div>'); //Add the fade layer to bottom of the body tag.
$('#fade').css({'filter' : 'alpha(opacity=80)'}).fadeIn(); //Fade in the fade layer - .css({'filter' : 'alpha(opacity=80)'}) is used to fix the IE Bug on fading transparencies
return false;
});
//Close Popups and Fade Layer
$('a.close, #fade').live('click', function() { //When clicking on the close or fade layer...
$('#fade , .popup_block').fadeOut(function() {
$('#fade, a.close').remove(); //fade them both out
});
return false;
});
});
</script>
<script>
var NumIms = 0;
var NumTxts = 0;
//IMAGE VARIABLES
var ImIds=[];
var ImNm=[];
var ImWdth=[];
var ImHght=[];
//TEXT VARIABLES
var TxtIds=[];
var Txt=[];
var TxtFnt=[];
var TxtCol=[];
var TxtSz=[];
var MyWidth;
var MyHeight;
var img;
function MoveOver(id,Rid) {
var img = new Image();
img.src = Rid;
MyWidth = img.width;
MyHeight = img.height;
$("#UpIm" + id).append("W=" + MyWidth + " H=" + MyHeight);
$("#containment-wrapper").append('<div id="AdIm' + id + '" class="draggable ui-widget-content" style="width:' + MyWidth + 'px; height:' + MyHeight + 'px; background-image: url(' + Rid + '); position:absolute; left:18px; top:18px;"></div>');
ImIds[id]="AdIm" + id;
ImNm[id]=Rid;
ImWdth[id]=MyWidth;
ImHght[id]=MyHeight;
$( "#AdIm" + id ).draggable();
var f = document.getElementById('UpIm' +id);
var Olddiv = document.getElementById('ul' + id);
f.removeChild(Olddiv);
}
</script>
<script>
function removeIm(id) {
var f = document.getElementById('files');
var Folddiv = document.getElementById('UpIm' + id);
f.removeChild(Folddiv);
var d = document.getElementById('containment-wrapper');
var Dolddiv = document.getElementById('AdIm' + id);
d.removeChild(Dolddiv);
ImIds.splice(id,1,"deleted");
}
</script>
<script type="text/javascript" >
var iid = -1;
var pic_real_width, pic_real_height, img;
function removeFormIm(Rid,id) {
var f = document.getElementById('files');
var Folddiv = document.getElementById('UpIm' + id);
f.removeChild(Folddiv);
var d = document.getElementById('containment-wrapper');
var Dolddiv = document.getElementById('AdIm' + id);
d.removeChild(Folddiv);
}
</script>
<style>
#containment-wrapper { width: 845px; height:150px; border:2px solid #ccc; }
#fade { /*--Transparent background layer--*/
display: none; /*--hidden by default--*/
background: #000;
position: fixed; left: 0; top: 0;
width: 100%; height: 100%;
opacity: .80;
z-index: 9999;
}
.popup_block{
display: none; /*--hidden by default--*/
background: #fff;
padding: 20px;
border: 20px solid #ddd;
float: left;
font-size: 1.2em;
position: fixed;
top: 50%; left: 50%;
z-index: 99999;
/*--CSS3 Box Shadows--*/
-webkit-box-shadow: 0px 0px 20px #000;
-moz-box-shadow: 0px 0px 20px #000;
box-shadow: 0px 0px 20px #000;
/*--CSS3 Rounded Corners--*/
-webkit-border-radius: 10px;
-moz-border-radius: 10px;
border-radius: 10px;
}
.t_t{
display: none; /*--hidden by default--*/
background: #fff;
padding: 20px;
border: 20px solid #ddd;
float: left;
font-size: 1.2em;
position: fixed;
top: 50%; left: 50%;
z-index: 99999;
/*--CSS3 Box Shadows--*/
-webkit-box-shadow: 0px 0px 20px #000;
-moz-box-shadow: 0px 0px 20px #000;
box-shadow: 0px 0px 20px #000;
/*--CSS3 Rounded Corners--*/
-webkit-border-radius: 10px;
-moz-border-radius: 10px;
border-radius: 10px;
}
img.btn_close {
float: right;
margin: -55px -55px 0 0;
}
/*--Making IE6 Understand Fixed Positioning--*/
*html #fade {
position: absolute;
}
*html .popup_block {
position: absolute;
}
</style>
<script>
function changeTxt(id){
var my_txt;
my_txt = document.getElementById('TxtIn' + id).value;
document.getElementById('AdText' + id).innerHTML = my_txt;
Txt[id] = my_txt;
}
</script>
<script>
function makebold(id){
$('#TxtIn' + id).insertAtCaret('<b></b>');
changeTxt(id);
}
function makeitalic(id){
$('#TxtIn' + id).insertAtCaret('<i></i>');
changeTxt(id);
}
function makecenter(id){
var my_txt;
my_txt = document.getElementById('TxtIn' + id).value;
$("textarea#TxtIn" + id).val('<center>' + my_txt + '</center>');
changeTxt(id)
}
function makebr(id){
$('#TxtIn' + id).insertAtCaret('<br>');
changeTxt(id);
}
function makelink(id){
get_color = document.getElementById('fcolor' + id).value;
$('#TxtIn' + id).insertAtCaret('<a href="http://" style="text-decoration:none; color:#' + get_color + ';"></a>');
changeTxt(id);
}
function makeh2(id){
$('#TxtIn' + id).insertAtCaret('<H2></H2>');
changeTxt(id);
}
function makeh3(id){
$('#TxtIn' + id).insertAtCaret('<H3></H3>');
changeTxt(id);
}
</script>
<script>
function callFontType(id){
var type;
type = document.getElementById('ftype' + id).value;
document.getElementById('AdText' + id).style.fontFamily=type;
TxtFnt[id] = type;
}
</script>
<script>
function CxColor(id){
var Clor;
Clor = document.getElementById('fcolor' + id).value;
Clor = '#' + Clor;
document.getElementById('AdText' + id).style.color=Clor;
TxtCol[id] = Clor;
}
</script>
<script>
function changeFSize(id){
var my_size;
my_size = document.getElementById('SizeIn' + id).value;
my_size = my_size + 'px';
document.getElementById('AdText' + id).style.fontSize = my_size;
TxtSz[id] = my_size;
}
</script>
<script>
var id = -1;
function addFormField() {
id = id + 1;
$("#divTxt").append("<span id='row" + id + "'><small>Add: to textbox:</small><input value=\"b\" onclick=\"makebold(" + id + ")\" title=\"bold: <b>text</b>\" type=\"button\"><input value=\"i\" onclick=\"makeitalic(" + id + ")\" title=\"italic: <i>text</i>\" type=\"button\"><input value=\"center\" onclick=\"makecenter(" + id + ")\" title=\"center: <center>text</center>\" type=\"button\"><input value=\"BR\" onclick=\"makebr(" + id + ")\" title=\"BR: <br>\" type=\"button\"><input value=\"link\" onclick=\"makelink(" + id + ")\" title=\"link: <a href= >URL</a>\" type=\"button\"><input value=\"H2\" onclick=\"makeh2(" + id + ")\" title=\"H2: <H2>text</H2>\" type=\"button\"><input value=\"H3\" onclick=\"makeh3(" + id + ")\" title=\"H3: <H3>text</H3>\" type=\"button\"><br><table><tr><td><a onClick='removeFormField(\"#row" + id + "\",\"" + id + "\"); return false;'>REMOVE</a></td><td> <textarea cols=50 rows=5 name='txt[]' id='TxtIn" + id + "' onKeyUp=\"changeTxt(" + id + ");\">Text " + id + "</textarea></td><td>Font:<select onChange=\"callFontType(" + id + ");\" id=\"ftype" + id + "\"><option value=\"Arial, Helvetica, sans-serif\">Arial</option><option value=\"Impact, Charcoal, sans-serif\">Impact</option><option value=\"Palatino Linotype, Book Antiqua, Palatino, serif\">Palatino</option><option value=\"Tahoma, Geneva, sans-serif\">Tahoma</option><option value=\"Century Gothic, sans-serif\">Century Gothic</option><option value=\"Lucida Sans Unicode, Lucida Grande, sans-serif\">Lucida Grande</option><option value=\"Arial Black, Gadget, sans-serif\">Arial Black</option><option value=\"Times New Roman, Times, serif\">Times New Roman</option><option value=\"Arial Narrow, sans-serif\">Arial Narrow</option><option value=\"Verdana, Geneva, sans-serif\">Verdana</option><option value=\"Copperplate, Copperplate Gothic Light, sans-serif\">Copperplate</option><option value=\"Lucida Console, Monaco, monospace\">Lucida Console</option><option value=\"Gill Sans, Gill Sans MT, sans-serif\">Gill Sans</option><option value=\"Trebuchet MS, Helvetica, sans-serif\">Trebuchet</option><option value=\"Courier New, Courier, monospace\">Courier New</option><option value=\"Georgia, Serif\">Georgia</option></select><br>Color: <input id=\"fcolor" + id + "\" class=\"color\" value=\"000000\"><img src=\"go.png\" style=\"vertical-align:middle;\" onClick='CxColor(" + id + ");'><br>Size: <input type='text' size='4' value=\"12\" name='txt[]' id='SizeIn" + id + "' onKeyUp=\"changeFSize(" + id + ");\"></td></tr></table><br><hr style=\"width:800px; float:left;\"><br></span>");
$("#containment-wrapper").append('<span id="AdText' + id + '" class="draggable ui-widget-content" style="position:absolute; left:18px; top:18px; font-size:16px; font-family:Arial, Helvetica, sans-serif;">Text ' + id + '</span>');
$( "#AdText" + id ).draggable();//{ containment: "#containment-wrapper", scroll: true }
$('#fcolor' + id).load(jscolor.init());
TxtIds[id] = "AdText" + id;
Txt[id] = "Ad Text";
TxtFnt[id] = "Arial";
TxtCol[id] = "#000000";
TxtSz[id] = "16";
$('#row' + id).highlightFade({
speed:1000
});
document.getElementById("id").value = id;
}
function removeFormField(Rid,id) {
$(Rid).remove();
var d = document.getElementById('containment-wrapper');
var olddiv = document.getElementById('AdText' + id);
d.removeChild(olddiv);
TxtIds.splice(id,1,"deleted");
}
function GetURL(id) {
var gurl;
var Ims = "";
var len=ImIds.length;
NumIms = 0;
NumTxts = 0;
//############ Start Get Images for URL ##############
for(var i=0; i<len; i++) {
NumIms++;
var value = ImIds[i];
Ims += '&ImName' + i + '=' + value;
if (value != "deleted"){
value = ImNm[i];
Ims += '&ImNm' + i + '=' + value;
value = ImWdth[i];
Ims += '&ImWidth' + i + '=' + value;
value = ImHght[i];
Ims += '&ImHeight' + i + '=' + value;
value = $('#AdIm' + i).position().left - $('#AdIm' + i).closest('#containment-wrapper').position().left;
Ims += '&ImLt' + i + '=' + value;
value = $('#AdIm' + i).position().top - $('#AdIm' + i).closest('#containment-wrapper').position().top;
Ims += '&ImTop' + i + '=' + value;
}
}
//########### End Get Images For URL #####################
len=TxtIds.length;
//############ Start Get Texts for URL ##############
for(var i=0; i<len; i++) {
NumTxts++;
var value = TxtIds[i];
Ims += '&TxtName' + i + '=' + escape(value);
if (value != "deleted"){
value = Txt[i];
Ims += '&Txt' + i + '=' + escape(value);
value = TxtFnt[i];
Ims += '&TxtFnt' + i + '=' + escape(value);
value = TxtCol[i];
value = value.substring(1);
Ims += '&TxtCol' + i + '=' + escape(value);
value = TxtSz[i];
Ims += '&TxtSz' + i + '=' + escape(value);
value = $('#AdText' + i).position().left - $('#AdText' + i).closest('#containment-wrapper').position().left;
Ims += '&TxtLt' + i + '=' + value;
value = $('#AdText' + i).position().top - $('#AdText' + i).closest('#containment-wrapper').position().top;
Ims += '&TxtTop' + i + '=' + value;
}
}
//########### End Get Texts For URL #####################
gurl = "ad.php?AdType=hero&ImNum=" + NumIms + "&TxtNum=" + NumTxts;
gurl = gurl + Ims;
//alert(gurl);gurl = escape( gurl );
$("#genurl" + id).html('<textarea id="fe_text" cols=50 rows=5 name="ad_url">' + gurl + '</textarea><br><br><table><tr><td><font style="font-family:Arial, Helvetica, sans-serif; font-size:16px; color:#009999">Preview Gernerated Ad:</font></td><td><a href="' + gurl + '" target="_blank"><img src="view.png"></a></td></tr></table><br>');
}
</script>
<script type="text/javascript">
$(document).ready(function(){
$("#myform1").validate({
debug: false,
submitHandler: function(form) {
// do other stuff for a valid form
$.post('process.php', $("#myform1").serialize(), function(data) {
$('#results').fadeIn('fast');
var mySplitResult = data.split("|||");
if(mySplitResult[1] !== "fail" && mySplitResult[1] !== "disable"){
$('#upd1').html('<textarea id="fe_text" cols=50 rows=5 readonly="readonly">' + mySplitResult[1] + '</textarea><br />');
}
$('#results').html(mySplitResult[0]);
$('#prev1').html(mySplitResult[1]);
setTimeout(function() {
$('#results').fadeOut('slow');
}, 2500);
});
}
});
});
</script>
<script type="text/javascript" src="jscolor.js"></script>
</head>
<body>
<div id="containment-wrapper">
<!--<span id="AdText0" class="draggable ui-widget-content">For Testing ... </span> -->
</div>
<div style="margin-left:50px;">
<center><p style="font-family:Arial, Helvetica, sans-serif; font-size:24px; color:#FF0099">Text Field Input</p>
<p><a href="#" onClick="addFormField(); return false;" style="font-family:Arial, Helvetica, sans-serif; font-size:16px; color:#6633FF;">Add Text Field</a></p></center>
<form action="#" method="get" id="form1" style="font-family:Arial, Helvetica, sans-serif; font-size:16px;">
<input type="hidden" id="id" value="1">
<div id="divTxt"></div>
</form>
</div>
<!-- End Hidden Divs -->
</body>
</html>