我正在创建一个可在Lampix（将基于触摸的界面投射到平面上的灯）上运行的应用程序。该应用程序需要包括基于触摸的绘图。为了使自己熟悉必要的编码，我找到了一个简单的“ sketchpad”的示例代码。我已将该代码复制并粘贴到用于该应用程序的现有index.html文件中。我正在本地主机上运行html，当我这样做时，似乎javascript方面无法正常工作。
在我从（https://zipso.net/a-simple-touchscreen-sketchpad-using-javascript-and-html5/）抓取此代码的网站上，他们有正在执行的代码的示例，而我的触摸屏计算机允许我在空白处画图。因此，我认为这不是浏览器兼容性问题。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Lampix App Starter</title>
<link rel="stylesheet" type="text/css" href="styles.css">
<script type="text/javascript">
// Variables for referencing the canvas and 2dcanvas context
var canvas,ctx;
// Variables to keep track of the mouse position and left-button status
var mouseX,mouseY,mouseDown=0;
// Variables to keep track of the touch position
var touchX,touchY;
// Keep track of the old/last position when drawing a line
// We set it to -1 at the start to indicate that we don't have a good value for it yet
var lastX,lastY=-1;
// Draws a line between the specified position on the supplied canvas name
// Parameters are: A canvas context, the x position, the y position, the size of the dot
function drawLine(ctx,x,y,size) {
// If lastX is not set, set lastX and lastY to the current position
if (lastX==-1) {
lastX=x;
lastY=y;
}
// Let's use black by setting RGB values to 0, and 255 alpha (completely opaque)
r=0; g=0; b=0; a=255;
// Select a fill style
ctx.strokeStyle = "rgba("+r+","+g+","+b+","+(a/255)+")";
// Set the line "cap" style to round, so lines at different angles can join into each other
ctx.lineCap = "round";
//ctx.lineJoin = "round";
// Draw a filled line
ctx.beginPath();
// First, move to the old (previous) position
ctx.moveTo(lastX,lastY);
// Now draw a line to the current touch/pointer position
ctx.lineTo(x,y);
// Set the line thickness and draw the line
ctx.lineWidth = size;
ctx.stroke();
ctx.closePath();
// Update the last position to reference the current position
lastX=x;
lastY=y;
}
// Clear the canvas context using the canvas width and height
function clearCanvas(canvas,ctx) {
ctx.clearRect(0, 0, canvas.width, canvas.height);
}
// Keep track of the mouse button being pressed and draw a dot at current location
function sketchpad_mouseDown() {
mouseDown=1;
drawLine(ctx,mouseX,mouseY,12);
}
// Keep track of the mouse button being released
function sketchpad_mouseUp() {
mouseDown=0;
// Reset lastX and lastY to -1 to indicate that they are now invalid, since we have lifted the "pen"
lastX=-1;
lastY=-1;
}
// Keep track of the mouse position and draw a dot if mouse button is currently pressed
function sketchpad_mouseMove(e) {
// Update the mouse co-ordinates when moved
getMousePos(e);
// Draw a dot if the mouse button is currently being pressed
if (mouseDown==1) {
drawLine(ctx,mouseX,mouseY,12);
}
}
// Get the current mouse position relative to the top-left of the canvas
function getMousePos(e) {
if (!e)
var e = event;
if (e.offsetX) {
mouseX = e.offsetX;
mouseY = e.offsetY;
}
else if (e.layerX) {
mouseX = e.layerX;
mouseY = e.layerY;
}
}
// Draw something when a touch start is detected
function sketchpad_touchStart() {
// Update the touch co-ordinates
getTouchPos();
drawLine(ctx,touchX,touchY,12);
// Prevents an additional mousedown event being triggered
event.preventDefault();
}
function sketchpad_touchEnd() {
// Reset lastX and lastY to -1 to indicate that they are now invalid, since we have lifted the "pen"
lastX=-1;
lastY=-1;
}
// Draw something and prevent the default scrolling when touch movement is detected
function sketchpad_touchMove(e) {
// Update the touch co-ordinates
getTouchPos(e);
// During a touchmove event, unlike a mousemove event, we don't need to check if the touch is engaged, since there will always be contact with the screen by definition.
drawLine(ctx,touchX,touchY,12);
// Prevent a scrolling action as a result of this touchmove triggering.
event.preventDefault();
}
// Get the touch position relative to the top-left of the canvas
// When we get the raw values of pageX and pageY below, they take into account the scrolling on the page
// but not the position relative to our target div. We'll adjust them using "target.offsetLeft" and
// "target.offsetTop" to get the correct values in relation to the top left of the canvas.
function getTouchPos(e) {
if (!e)
var e = event;
if(e.touches) {
if (e.touches.length == 1) { // Only deal with one finger
var touch = e.touches[0]; // Get the information for finger #1
touchX=touch.pageX-touch.target.offsetLeft;
touchY=touch.pageY-touch.target.offsetTop;
}
}
}
// Set-up the canvas and add our event handlers after the page has loaded
function init() {
// Get the specific canvas element from the HTML document
canvas = document.getElementById('sketchpad');
// If the browser supports the canvas tag, get the 2d drawing context for this canvas
if (canvas.getContext)
ctx = canvas.getContext('2d');
// Check that we have a valid context to draw on/with before adding event handlers
if (ctx) {
// React to mouse events on the canvas, and mouseup on the entire document
canvas.addEventListener('mousedown', sketchpad_mouseDown, false);
canvas.addEventListener('mousemove', sketchpad_mouseMove, false);
window.addEventListener('mouseup', sketchpad_mouseUp, false);
// React to touch events on the canvas
canvas.addEventListener('touchstart', sketchpad_touchStart, false);
canvas.addEventListener('touchend', sketchpad_touchEnd, false);
canvas.addEventListener('touchmove', sketchpad_touchMove, false);
}
}
</script>
<style>
html, body {
margin: 0;
padding: 0;
width: 100vw;
height: 100vh;
overflow: hidden;
background: white;
font-family: 'Helvetica', sans-serif;
color: navy;
}
ul.a { /*bulleted list for object description*/
list-style-type: circle;
/* Some CSS styling */
#sketchpadapp {
/* Prevent nearby text being highlighted when accidentally dragging mouse outside confines of the canvas */
-webkit-touch-callout: none;
-webkit-user-select: none;
-khtml-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
}
.leftside {
float:left;
width:220px;
height:285px;
background-color:#def;
padding:10px;
border-radius:4px;
}
.rightside {
float:left;
margin-left:10px;
}
#sketchpad {
float:left;
height:300px;
width:400px;
border:2px solid #888;
border-radius:4px;
position:relative; /* Necessary for correct mouse co-ords in Firefox */
}
#clearbutton {
font-size: 15px;
padding: 10px;
-webkit-appearance: none;
background: #eee;
border: 1px solid #888;
}
</style>
</head>
<body>
<div id="sketchpadapp">
<div class="leftside">
Touchscreen and mouse support HTML5 canvas sketchpad.<br/><br/>
Draw something by tapping or dragging.<br/><br/>
Works on iOS, Android and desktop/laptop touchscreens using Chrome/Firefox/Safari.<br/><br/>
<input type="submit" value="Clear Sketchpad" id="clearbutton" onclick="clearCanvas(canvas,ctx);">
</div>
<div class="rightside">
<canvas id="sketchpad" height="300" width="400">
</canvas>
</div>
</div>
</body>
</html>
您应该可以触摸或单击指定的框，并且会出现一个黑点。如果单击并拖动，将会出现很多点，从而产生有点像摇晃的线条的效果。