Apply Tab's proposal for blur radius <http://lists.w3.org/Archives/Public/www-style/2010Jul/0464.html>

Author: fantasai

css3-background/Overview.html

@@ -22,12 +22,12 @@
 
    <h1>CSS Backgrounds and Borders Module Level 3</h1>
 
-   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 21 June 2010</h2>
+   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 24 August 2010</h2>
 
    <dl>
     <dt>This version:
 
-    <dd><!--<a href="http://www.w3.org/TR/2010/WD-css3-background-20100621">http://www.w3.org/TR/2010/ED-css3-background-20100621</a>-->
+    <dd><!--<a href="http://www.w3.org/TR/2010/WD-css3-background-20100824">http://www.w3.org/TR/2010/ED-css3-background-20100824</a>-->
      <a
      href="http://dev.w3.org/csswg/css3-background">http://dev.w3.org/csswg/css3-background</a>
 
@@ -3722,9 +3722,9 @@ <h3 id=the-box-shadow><span class=secno>7.2. </span>The &lsquo;<a
    <li>The second length is the vertical offset. A positive value offsets the
     shadow down, a negative one up.
 
-   <li>The third length is a blur distance. Negative values are not allowed.
-    If the blur value is zero, the shadow's edge is sharp. Otherwise, the
-    larger the value, the more the shadow's edge is blurred. See below.
+   <li>The third length is a blur radius. Negative values are not allowed. If
+    the blur value is zero, the shadow's edge is sharp. Otherwise, the larger
+    the value, the more the shadow's edge is blurred. See below.
 
    <li>The fourth length is a spread distance. Positive values cause the
     shadow shape to expand in all directions by the specified radius.
@@ -3777,11 +3777,17 @@ <h3 id=the-box-shadow><span class=secno>7.2. </span>The &lsquo;<a
 
   <p>A non-zero blur distance indicates that the resulting shadow should be
    blurred, such as by a Gaussian filter. The exact algorithm is not defined;
-   however for a long, straight shadow edge, this should create a color
-   transition the length of the blur distance that is perpendicular to and
-   centered on the shadow's edge, and that ranges from the full shadow color
-   at the radius endpoint inside the shadow to fully transparent at the
-   endpoint outside it.
+   however the resulting shadow must approximate (with each pixel being
+   within 5% of its expected value) the image that would be generated by
+   applying to the shadow a Gaussian blur with a standard deviation equal to
+   the blur radius
+
+  <p class=note>Note this means for a long, straight shadow edge, the blur
+   radius will create a visibly apparent color transition approximately the
+   twice length of the blur radius that is perpendicular to and centered on
+   the shadow's edge, and that ranges from the full shadow color at the
+   endpoint inside the shadow to fully transparent at the endpoint outside
+   it.
 
   <div class=example>
    <p>The example below demonstrates the effects of spread and blur on the

css3-background/Overview.src.html

@@ -2698,7 +2698,7 @@ <h3 id="the-box-shadow">The 'box-shadow' property</h3>
   <li>The second length is the vertical offset. A positive value
   offsets the shadow down, a negative one up.
 
-  <li>The third length is a blur distance. Negative values are not
+  <li>The third length is a blur radius. Negative values are not
   allowed. If the blur value is zero, the shadow's edge is sharp.
   Otherwise, the larger the value, the more the shadow's edge is
   blurred. See below.
@@ -2754,11 +2754,16 @@ <h3 id="the-box-shadow">The 'box-shadow' property</h3>
 
 <p>A non-zero blur distance indicates that the resulting shadow should
 be blurred, such as by a Gaussian filter. The exact algorithm is not
-defined; however for a long, straight shadow edge, this should create
-a color transition the length of the blur distance that is perpendicular
-to and centered on the shadow's edge, and that ranges from the full
-shadow color at the radius endpoint inside the shadow to fully
-transparent at the endpoint outside it.
+defined; however the resulting shadow must approximate (with each pixel
+being within 5% of its expected value) the image that would be generated
+by applying to the shadow a Gaussian blur with a standard deviation equal
+to the blur radius
+
+<p class="note">Note this means for a long, straight shadow edge, the
+blur radius will create a visibly apparent color transition approximately
+the twice length of the blur radius that is perpendicular to and centered
+on the shadow's edge, and that ranges from the full shadow color at the
+endpoint inside the shadow to fully transparent at the endpoint outside it.
 
 <div class="example">
 <p>The example below demonstrates the effects of spread and blur