Add advances to TextMetrics and change baselines API

This changes the canvas TextMetrics interface mixin in two ways:

* It adds an advances attribute, for the advances of each character.
* It changes the baselines-retrieval API from separate attributes to a
  dictionary returned by a getBaselines() method.

Author: fserb

source

@@ -60014,10 +60014,18 @@ interface <dfn>CanvasPattern</dfn> {
   void <span data-x="dom-canvaspattern-setTransform">setTransform</span>(optional <span>DOMMatrix2DInit</span> transform);
 };
 
+[Exposed=(Window,Worker)]
+dictionary <dfn>Baselines</dfn> {
+  double <span data-x="dom-Baselines-alphabetic">alphabetic</span>;
+  double <span data-x="dom-Baselines-hanging">hanging</span>;
+  double <span data-x="dom-Baselines-ideographic">ideographic</span>;
+};
+
 [Exposed=(Window,Worker)]
 interface <dfn>TextMetrics</dfn> {
   // x-direction
   readonly attribute double <span data-x="dom-textmetrics-width">width</span>; // advance width
+  readonly attribute FrozenArray&lt;double> <span data-x="dom-textmetrics-advances">advances</span>;
   readonly attribute double <span data-x="dom-textmetrics-actualBoundingBoxLeft">actualBoundingBoxLeft</span>;
   readonly attribute double <span data-x="dom-textmetrics-actualBoundingBoxRight">actualBoundingBoxRight</span>;
 
@@ -60028,9 +60036,7 @@ interface <dfn>TextMetrics</dfn> {
   readonly attribute double <span data-x="dom-textmetrics-actualBoundingBoxDescent">actualBoundingBoxDescent</span>;
   readonly attribute double <span data-x="dom-textmetrics-emHeightAscent">emHeightAscent</span>;
   readonly attribute double <span data-x="dom-textmetrics-emHeightDescent">emHeightDescent</span>;
-  readonly attribute double <span data-x="dom-textmetrics-hangingBaseline">hangingBaseline</span>;
-  readonly attribute double <span data-x="dom-textmetrics-alphabeticBaseline">alphabeticBaseline</span>;
-  readonly attribute double <span data-x="dom-textmetrics-ideographicBaseline">ideographicBaseline</span>;
+  <span>Baselines</span> <span data-x="dom-textmetrics-getBaselines">getBaselines</span>();
 };
 
 [<span data-x="dom-imagedata">Constructor</span>(unsigned long sw, unsigned long sh),
@@ -62953,6 +62959,7 @@ try {
    </dd>
 
    <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-width">width</code></dt>
+   <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-advances">advances</code></dt>
    <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-actualBoundingBoxLeft">actualBoundingBoxLeft</code></dt>
    <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-actualBoundingBoxRight">actualBoundingBoxRight</code></dt>
    <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-fontBoundingBoxAscent">fontBoundingBoxAscent</code></dt>
@@ -62961,9 +62968,7 @@ try {
    <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-actualBoundingBoxDescent">actualBoundingBoxDescent</code></dt>
    <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-emHeightAscent">emHeightAscent</code></dt>
    <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-emHeightDescent">emHeightDescent</code></dt>
-   <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-hangingBaseline">hangingBaseline</code></dt>
-   <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-alphabeticBaseline">alphabeticBaseline</code></dt>
-   <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-ideographicBaseline">ideographicBaseline</code></dt>
+   <dt><var>metrics</var> . <code subdfn data-x="dom-textmetrics-getBaselines">getBaselines</code>()</dt>
 
    <dd>
 
@@ -63150,7 +63155,7 @@ v6DVT (also check for '- -' bits in the part above) -->
   argument, <var>text</var>. When the method is invoked, the user agent must run the
   <span>text preparation algorithm</span>, passing it <var>text</var> and the object implementing
   the <code>CanvasText</code> interface, and then using the returned <span>inline box</span> must
-  create a new <code>TextMetrics</code> object with its attributes set as described in the following
+  create a new <code>TextMetrics</code> object with members behaving as described in the following
   list.
 <!--ADD-TOPIC:Security-->
   If doing these measurements requires using a font that has an <span>origin</span> that is not the
@@ -63173,6 +63178,13 @@ v6DVT (also check for '- -' bits in the part above) -->
    <dd><p>The width of that <span>inline box</span>, in <span data-x="'px'">CSS pixels</span>. (The
    text's advance width.)</p></dd>
 
+   <dt><dfn><code data-x="dom-textmetrics-advances">advances</code></dfn> attribute</dt>
+
+   <dd><p>Returns a frozen array containing advances for each character in the measured text. Each
+   advance is measured as the distance from the beginning of the string (starting at 0) up to the
+   left side of the character. The same frozen array object must be returned every time this
+   attribute's getter is invoked.</p></dd>
+
    <dt><dfn><code data-x="dom-textmetrics-actualBoundingBoxLeft">actualBoundingBoxLeft</code></dfn> attribute</dt>
 
    <dd>
@@ -63270,30 +63282,31 @@ v6DVT (also check for '- -' bits in the part above) -->
    indicating that the given baseline is below the bottom of that em square (so this value will
    usually be negative). (Zero if the given baseline is the bottom of that em square.)</p></dd>
 
-   <dt><dfn><code data-x="dom-textmetrics-hangingBaseline">hangingBaseline</code></dfn> attribute</dt>
-
-   <dd><p>The distance from the horizontal line indicated by the <code
-   data-x="dom-context-2d-textBaseline">textBaseline</code> attribute to the hanging baseline of the
-   <span>line box</span>, in <span data-x="'px'">CSS pixels</span>; positive numbers indicating that
-   the given baseline is below the hanging baseline. (Zero if the given baseline is the hanging
-   baseline.)</p></dd>
+   <dt><dfn><code data-x="dom-textmetrics-getBaselines">getBaselines()</code></dfn> method</dt>
 
-   <dt><dfn><code data-x="dom-textmetrics-alphabeticBaseline">alphabeticBaseline</code></dfn> attribute</dt>
+   <dd>
+    <p>Returns a <code>Baselines</code> dictionary containing available baselines:
 
-   <dd><p>The distance from the horizontal line indicated by the <code
-   data-x="dom-context-2d-textBaseline">textBaseline</code> attribute to the alphabetic baseline of
-   the <span>line box</span>, in <span data-x="'px'">CSS pixels</span>; positive numbers indicating
-   that the given baseline is below the alphabetic baseline. (Zero if the given baseline is the
-   alphabetic baseline.)</p></dd>
+    <ul>
+     <li><p>If the alphabetic baseline is available for this text, the <dfn><code
+     data-x="dom-Baselines-alphabetic">alphabetic</code></dfn> dictionary member must be set to that
+     baseline value.</p></li>
 
-   <dt><dfn><code data-x="dom-textmetrics-ideographicBaseline">ideographicBaseline</code></dfn> attribute</dt>
+     <li><p>If the hanging baseline is available for this text, the <dfn><code
+     data-x="dom-Baselines-hanging">hanging</code></dfn> dictionary member must be set to that
+     baseline value.</p></li>
 
-   <dd><p>The distance from the horizontal line indicated by the <code
-   data-x="dom-context-2d-textBaseline">textBaseline</code> attribute to the ideographic baseline of
-   the <span>line box</span>, in <span data-x="'px'">CSS pixels</span>; positive numbers indicating
-   that the given baseline is below the ideographic baseline. (Zero if the given baseline is the
-   ideographic baseline.)</p></dd>
+     <li><p>If the ideographic baseline is available for this text, the <dfn><code
+     data-x="dom-Baselines-ideographic">ideographic</code></dfn> dictionary member must be set to
+     that baseline value.</p></li>
+    </ul>
 
+    <p>In all cases, the baslines values are represented as distance from the horizontal line
+    indicated by the <code data-x="dom-context-2d-textBaseline">textBaseline</code> attribute to
+    their respective baseline of the <span>line box</span>, in <span
+    data-x="'px'">CSS pixels</span>, with positive numbers indicating that the given baseline is
+    below the current <code data-x="dom-context-2d-textBaseline">textBaseline</code>.</p>
+   </dd>
   </dl>
 
   <p class="note">Glyphs rendered using <code data-x="dom-context-2d-fillText">fillText()</code> and