这是一个工作示例。
<html> <script type="text/javascript"> var canvas, ctx, flag = false, prevX = 0, currX = 0, prevY = 0, currY = 0, dot_flag = false; var x = "black", y = 2; function init() { canvas = document.getElementById('can'); ctx = canvas.getContext("2d"); w = canvas.width; h = canvas.height; canvas.addEventListener("mousemove", function (e) { findxy('move', e) }, false); canvas.addEventListener("mousedown", function (e) { findxy('down', e) }, false); canvas.addEventListener("mouseup", function (e) { findxy('up', e) }, false); canvas.addEventListener("mouseout", function (e) { findxy('out', e) }, false); } function color(obj) { switch (obj.id) { case "green": x = "green"; break; case "blue": x = "blue"; break; case "red": x = "red"; break; case "yellow": x = "yellow"; break; case "orange": x = "orange"; break; case "black": x = "black"; break; case "white": x = "white"; break; } if (x == "white") y = 14; else y = 2; } function draw() { ctx.beginPath(); ctx.moveTo(prevX, prevY); ctx.lineTo(currX, currY); ctx.strokeStyle = x; ctx.lineWidth = y; ctx.stroke(); ctx.closePath(); } function erase() { var m = confirm("Want to clear"); if (m) { ctx.clearRect(0, 0, w, h); document.getElementById("canvasimg").style.display = "none"; } } function save() { document.getElementById("canvasimg").style.border = "2px solid"; var dataURL = canvas.toDataURL(); document.getElementById("canvasimg").src = dataURL; document.getElementById("canvasimg").style.display = "inline"; } function findxy(res, e) { if (res == 'down') { prevX = currX; prevY = currY; currX = e.clientX - canvas.offsetLeft; currY = e.clientY - canvas.offsetTop; flag = true; dot_flag = true; if (dot_flag) { ctx.beginPath(); ctx.fillStyle = x; ctx.fillRect(currX, currY, 2, 2); ctx.closePath(); dot_flag = false; } } if (res == 'up' || res == "out") { flag = false; } if (res == 'move') { if (flag) { prevX = currX; prevY = currY; currX = e.clientX - canvas.offsetLeft; currY = e.clientY - canvas.offsetTop; draw(); } } } </script> <body onload="init()"> <canvas id="can" width="400" height="400" ></canvas> <div >Choose Color</div> <div id="green" onclick="color(this)"></div> <div id="blue" onclick="color(this)"></div> <div id="red" onclick="color(this)"></div> <div id="yellow" onclick="color(this)"></div> <div id="orange" onclick="color(this)"></div> <div id="black" onclick="color(this)"></div> <div >Eraser</div> <div id="white" onclick="color(this)"></div> <img id="canvasimg" > <input type="button" value="save" id="btn" size="30" onclick="save()" > <input type="button" value="clear" id="clr" size="23" onclick="erase()" > </body> </html>
