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POCanvas redraws only after loop ends
 

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    <p>I have an issue with drawing on canvas in a loop.</p> <p>What I want to achieve is that in each loop the script waits for a few milliseconds, then draws on a canvas, the user can actually see the change, and then the loop repeats.</p> <p>What it does instead is that the user can't see the change, until the for-loop ends.</p> <p>But I have found that if I show an alert window and the script waits for the user to respond, it actually draws the change.</p> <p>How to show "the small changes" in every loop, not just in the end?</p> <p>My code (<s>also here: <a href="http://janiczek.github.com/heighway-dragon/" rel="nofollow">http://janiczek.github.com/heighway-dragon/</a> </s> the link now contains something else):</p> <pre><code>&lt;script type="text/javascript"&gt; function sleep (ms) { var start = new Date().getTime(); while (new Date().getTime() &lt; start + ms) continue; }; function draw (withalert) { if (withalert == null) withalert = false; var cur_x = 100 - .5; var cur_y = 200 - .5; length = 3; steps = 20; c.strokeStyle = "#f00"; canvas.width = canvas.width; for (var count = 0; count &lt; steps; count++) { sleep(100); c.beginPath(); c.moveTo(cur_x, cur_y); cur_x += length; c.lineTo(cur_x, cur_y); c.stroke(); if (withalert) alert(count); } }; &lt;/script&gt; &lt;canvas id=canvas width=300 height=300 style="border: 2px solid #000"&gt;&lt;/canvas&gt;&lt;br&gt; &lt;input type="submit" value="Without alert" onclick="draw()"&gt; &lt;input type="submit" value="With alert" onclick="draw(true)"&gt; &lt;script type="text/javascript"&gt; var canvas = document.getElementById("canvas"); var c = canvas.getContext("2d"); &lt;/script&gt; </code></pre>
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    1. USMartin Janiczek
    1. USMartin Janiczek
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    1. COThe `if (withalert == null) withalert = false;` line is unnecessary, if `withalert` is `null` the `if (withalert)` check would fail properly.
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      1. USjball
    2. COjball, this code is just an "as-simple-as-possible" example of what I experience with larger code. I didn't want to put here the whole thing - only the parts where the problem lies. (and the button for alert isn't in the larger code - it's just to illustrate that it redraws if I hold it with something)
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      1. USMartin Janiczek
 

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