返回到:Canvas API:CanvasRenderingContext2D
本节课,我们学习CanvasRenderingContext2D.save()方法。
CanvasRenderingContext2D.save()
是 Canvas 2D API 通过将当前状态放入栈中,保存 canvas 全部状态的方法。
void ctx.save();
保存到栈中的绘制状态有下面部分组成:
strokeStyle
, fillStyle
, globalAlpha
, lineWidth
, lineCap
, lineJoin
, miterLimit
, lineDashOffset
, shadowOffsetX
, shadowOffsetY
, shadowBlur
, shadowColor
, globalCompositeOperation
, font
, textAlign
, textBaseline
, direction
, imageSmoothingEnabled
.save
方法这是一段简单的代码片段,使用 save
方法保存默认的状态,这样,稍后你就可以使用默认的设置绘制一个矩形。
<canvas id="canvas"></canvas>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.save(); // 保存默认的状态
ctx.fillStyle = "green";
ctx.fillRect(10, 10, 100, 100);
ctx.restore(); // 还原到上次保存的默认状态
ctx.fillRect(150, 75, 100, 100);
修改下面的代码并在线查看 canvas 的变化:
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta name="robots" content="noindex, nofollow"> <style> body { padding: 0; margin: 0; } svg:not(:root) { display: block; } .playable-code { background-color: #f4f7f8; border: none; border-left: 6px solid #558abb; border-width: medium medium medium 6px; color: #4d4e53; height: 100px; width: 90%; padding: 10px 10px 0; } .playable-canvas { border: 1px solid #4d4e53; border-radius: 2px; } .playable-buttons { text-align: right; width: 90%; padding: 5px 10px 5px 26px; } </style> <title>CanvasRenderingContext2D.save() | Web176教程www.web176.com</title> </head> <body> <canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas> <div class="playable-buttons"> <input id="edit" type="button" value="Edit" /> <input id="reset" type="button" value="Reset" /> </div> <textarea id="code" class="playable-code"> ctx.save(); ctx.fillStyle = "green"; ctx.fillRect(10, 10, 100, 100); ctx.restore(); ctx.fillRect(150, 75, 100, 100);</textarea> <script> var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); ctx.save(); // 保存默认的状态 ctx.fillStyle = "green"; ctx.fillRect(10, 10, 100, 100); ctx.restore(); // 还原到上次保存的默认状态 ctx.fillRect(150, 75, 100, 100); var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); var textarea = document.getElementById("code"); var reset = document.getElementById("reset"); var edit = document.getElementById("edit"); var code = textarea.value; function drawCanvas() { ctx.clearRect(0, 0, canvas.width, canvas.height); eval(textarea.value); } reset.addEventListener("click", function() { textarea.value = code; drawCanvas(); }); edit.addEventListener("click", function() { textarea.focus(); }) textarea.addEventListener("input", drawCanvas); window.addEventListener("load", drawCanvas); </script> </body> </html>