  <option value=0 select>0</option>
    <option value=22.5>22.5</option>
    <option value=45>45</option>
    <option value=67.5>67.5</option>
    <option value=90>90</option>
</select>

    Fill <input id='fillCheckbox' type='checkbox' checked/>
    <input id='eraseAllButton' type='button' value='Erase all'/>
</div>

<div id='dragDiv'>
    控制: <input type='checkbox' id='editCheckbox'/>
</div>

<script>
    /*
 * Copyright (C) 2012 David Geary. This code is from the book
 * Core HTML5 Canvas, published 