# [html5] r8294 - [giow] (3) Make arc() match reality better and contradict itself less. Fixing ht [...]

whatwg at whatwg.org whatwg at whatwg.org
Mon Nov 18 16:06:32 PST 2013

```Author: ianh
Date: 2013-11-18 16:06:30 -0800 (Mon, 18 Nov 2013)
New Revision: 8294

Modified:
complete.html
index
source
Log:
[giow] (3) Make arc() match reality better and contradict itself less.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=23050
Affected topics: Canvas

Modified: complete.html
===================================================================
--- complete.html	2013-11-18 23:34:34 UTC (rev 8293)
+++ complete.html	2013-11-19 00:06:30 UTC (rev 8294)
@@ -55270,20 +55270,26 @@

<p>Consider an ellipse that has its origin at (<var title="">x</var>, <var title="">y</var>), that
-  inclined <var title="">rotation</var> radians clockwise from the x-axis. The points at <var title="">startAngle</var> and <var title="">endAngle</var> along this circle's circumference,
-  measured in radians clockwise from the ellipse's semi-major axis, are the start and end points
-  respectively.</p>
+  inclined <var title="">rotation</var> radians clockwise from the x-axis.</p>

-  <p>If the <var title="">anticlockwise</var> argument is false and <span title=""><var title="">endAngle</var>-<var title="">startAngle</var></span> is equal to or greater than <span title="">2π</span>, or, if the <var title="">anticlockwise</var> argument is <em>true</em> and
-  <span title=""><var title="">startAngle</var>-<var title="">endAngle</var></span> is equal to or
-  greater than <span title="">2π</span>, then the arc is the whole circumference of this
-  ellipse.</p>
+  <p>If the <var title="">anticlockwise</var> argument is false and <span title=""><var title="">endAngle</var>-<var title="">startAngle</var></span> is equal to or greater than <span title="">2π</span>, or, if the <var title="">anticlockwise</var> argument is <em>true</em>
+  and <span title=""><var title="">startAngle</var>-<var title="">endAngle</var></span> is equal
+  to or greater than <span title="">2π</span>, then the arc is the whole circumference of this
+  ellipse, and the point at <var title="">startAngle</var> along this circle's circumference,
+  measured in radians clockwise from the ellipse's semi-major axis, acts as both the start point and
+  the end point.</p>

-  <p>Otherwise, the arc is the path along the circumference of this ellipse from the start point to
+<!--CLEANUP-->
+  <p>Otherwise, the points at <var title="">startAngle</var> and <var title="">endAngle</var> along this circle's circumference,
+  measured in radians clockwise from the ellipse's semi-major axis, are the start and end points
+  respectively, and the arc is the path along the circumference of this ellipse from the start point to
the end point, going anti-clockwise if the <var title="">anticlockwise</var> argument is true, and
clockwise otherwise. Since the points are on the ellipse, as opposed to being simply angles from
zero, the arc can never cover an angle greater than <span title="">2π</span> radians.</p>

+  <p class=note>Even if the arc covers the entire circumference of the ellipse and there are no
+  other points in the subpath, the path is not closed unless the <code title=dom-context-2d-closePath><a href=#dom-context-2d-closepath>closePath()</a></code> method is appropriately invoked.</p>
+
implementation to throw an <code><a href=#indexsizeerror>IndexSizeError</a></code> exception.</p>

Modified: index
===================================================================
--- index	2013-11-18 23:34:34 UTC (rev 8293)
+++ index	2013-11-19 00:06:30 UTC (rev 8294)
@@ -55270,20 +55270,26 @@

<p>Consider an ellipse that has its origin at (<var title="">x</var>, <var title="">y</var>), that
-  inclined <var title="">rotation</var> radians clockwise from the x-axis. The points at <var title="">startAngle</var> and <var title="">endAngle</var> along this circle's circumference,
-  measured in radians clockwise from the ellipse's semi-major axis, are the start and end points
-  respectively.</p>
+  inclined <var title="">rotation</var> radians clockwise from the x-axis.</p>

-  <p>If the <var title="">anticlockwise</var> argument is false and <span title=""><var title="">endAngle</var>-<var title="">startAngle</var></span> is equal to or greater than <span title="">2π</span>, or, if the <var title="">anticlockwise</var> argument is <em>true</em> and
-  <span title=""><var title="">startAngle</var>-<var title="">endAngle</var></span> is equal to or
-  greater than <span title="">2π</span>, then the arc is the whole circumference of this
-  ellipse.</p>
+  <p>If the <var title="">anticlockwise</var> argument is false and <span title=""><var title="">endAngle</var>-<var title="">startAngle</var></span> is equal to or greater than <span title="">2π</span>, or, if the <var title="">anticlockwise</var> argument is <em>true</em>
+  and <span title=""><var title="">startAngle</var>-<var title="">endAngle</var></span> is equal
+  to or greater than <span title="">2π</span>, then the arc is the whole circumference of this
+  ellipse, and the point at <var title="">startAngle</var> along this circle's circumference,
+  measured in radians clockwise from the ellipse's semi-major axis, acts as both the start point and
+  the end point.</p>

-  <p>Otherwise, the arc is the path along the circumference of this ellipse from the start point to
+<!--CLEANUP-->
+  <p>Otherwise, the points at <var title="">startAngle</var> and <var title="">endAngle</var> along this circle's circumference,
+  measured in radians clockwise from the ellipse's semi-major axis, are the start and end points
+  respectively, and the arc is the path along the circumference of this ellipse from the start point to
the end point, going anti-clockwise if the <var title="">anticlockwise</var> argument is true, and
clockwise otherwise. Since the points are on the ellipse, as opposed to being simply angles from
zero, the arc can never cover an angle greater than <span title="">2π</span> radians.</p>

+  <p class=note>Even if the arc covers the entire circumference of the ellipse and there are no
+  other points in the subpath, the path is not closed unless the <code title=dom-context-2d-closePath><a href=#dom-context-2d-closepath>closePath()</a></code> method is appropriately invoked.</p>
+
implementation to throw an <code><a href=#indexsizeerror>IndexSizeError</a></code> exception.</p>

Modified: source
===================================================================
--- source	2013-11-18 23:34:34 UTC (rev 8293)
+++ source	2013-11-19 00:06:30 UTC (rev 8294)
@@ -61253,23 +61253,30 @@
<p>Consider an ellipse that has its origin at (<var data-x="">x</var>, <var data-x="">y</var>), that
data-x="">radiusY</var>, and that is rotated about its origin such that its semi-major axis is
-  inclined <var data-x="">rotation</var> radians clockwise from the x-axis. The points at <var
-  data-x="">startAngle</var> and <var data-x="">endAngle</var> along this circle's circumference,
-  measured in radians clockwise from the ellipse's semi-major axis, are the start and end points
-  respectively.</p>
+  inclined <var data-x="">rotation</var> radians clockwise from the x-axis.</p>

<p>If the <var data-x="">anticlockwise</var> argument is false and <span data-x=""><var
data-x="">endAngle</var>-<var data-x="">startAngle</var></span> is equal to or greater than <span
-  data-x="">2π</span>, or, if the <var data-x="">anticlockwise</var> argument is <em>true</em> and
-  <span data-x=""><var data-x="">startAngle</var>-<var data-x="">endAngle</var></span> is equal to or
-  greater than <span data-x="">2π</span>, then the arc is the whole circumference of this
-  ellipse.</p>
+  data-x="">2π</span>, or, if the <var data-x="">anticlockwise</var> argument is <em>true</em>
+  and <span data-x=""><var data-x="">startAngle</var>-<var data-x="">endAngle</var></span> is equal
+  to or greater than <span data-x="">2π</span>, then the arc is the whole circumference of this
+  ellipse, and the point at <var data-x="">startAngle</var> along this circle's circumference,
+  measured in radians clockwise from the ellipse's semi-major axis, acts as both the start point and
+  the end point.</p>

-  <p>Otherwise, the arc is the path along the circumference of this ellipse from the start point to
+<!--CLEANUP-->
+  <p>Otherwise, the points at <var
+  data-x="">startAngle</var> and <var data-x="">endAngle</var> along this circle's circumference,
+  measured in radians clockwise from the ellipse's semi-major axis, are the start and end points
+  respectively, and the arc is the path along the circumference of this ellipse from the start point to
the end point, going anti-clockwise if the <var data-x="">anticlockwise</var> argument is true, and
clockwise otherwise. Since the points are on the ellipse, as opposed to being simply angles from
zero, the arc can never cover an angle greater than <span data-x="">2π</span> radians.</p>

+  <p class="note">Even if the arc covers the entire circumference of the ellipse and there are no
+  other points in the subpath, the path is not closed unless the <code
+  data-x="dom-context-2d-closePath">closePath()</code> method is appropriately invoked.</p>
+