[e] (0) Mention that getImageData() might return different pixel data…

… than you set, due to premultiplying. git-svn-id: http://svn.whatwg.org/webapps@3230 340c8d12-0b0e-0410-8428-c7bf67bfef74
whatwg · Jun 12, 2009 · 3b74ed3 · 3b74ed3
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diff --git a/index b/index
@@ -25546,6 +25546,12 @@ context.getImageData(0, 0, w, h);</pre>
   for all of the <code title=dom-context-2d-getImageData><a href=#dom-context-2d-getimagedata>createImageData()</a></code>, <code title=dom-context-2d-getImageData><a href=#dom-context-2d-getimagedata>getImageData()</a></code> and <code title=dom-context-2d-putImageData><a href=#dom-context-2d-putimagedata>putImageData()</a></code>
   operations.</p>
 
+  <p class=note>Due to the lossy nature of converting to and from
+  premultiplied alpha color values, pixels that have just been set
+  using <code title=dom-context-2d-putImageData><a href=#dom-context-2d-putimagedata>putImageData()</a></code> might be
+  returned to an equivalent <code title=dom-context-2d-getImageData><a href=#dom-context-2d-getimagedata>getImageData()</a></code> as
+  different values.</p>
+
   <p>The current path, <a href=#transformations title=dom-context-2d-transformation>transformation matrix</a>,
   <a href=#shadows title=shadows>shadow attributes</a>, <a href=#dom-context-2d-globalalpha title=dom-context-2d-globalAlpha>global alpha</a>, the <a href=#clipping-region title="clipping region">clipping region</a>, and <a href=#dom-context-2d-globalcompositeoperation title=dom-context-2d-globalCompositeOperation>global composition
   operator</a> must not affect the <code title=dom-context-2d-getImageData><a href=#dom-context-2d-getimagedata>getImageData()</a></code> and <code title=dom-context-2d-putImageData><a href=#dom-context-2d-putimagedata>putImageData()</a></code>

diff --git a/source b/source
@@ -28085,6 +28085,14 @@ context.getImageData(0, 0, w, h);</pre>
   title="dom-context-2d-putImageData">putImageData()</code>
   operations.</p>
 
+  <p class="note">Due to the lossy nature of converting to and from
+  premultiplied alpha color values, pixels that have just been set
+  using <code
+  title="dom-context-2d-putImageData">putImageData()</code> might be
+  returned to an equivalent <code
+  title="dom-context-2d-getImageData">getImageData()</code> as
+  different values.</p>
+
   <p>The current path, <span
   title="dom-context-2d-transformation">transformation matrix</span>,
   <span title="shadows">shadow attributes</span>, <span