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Add a lang IDL Attribute to CanvasTextDrawingStyles, and clarify "direction" on same #10873

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Add a lang IDL Attribute to CanvasTextDrawingStyles, and clarify "direction" on same #10873

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eba506c
Add the lang IDL attribute to CanvasTextDrawingStyles
schenney-chromium Dec 18, 2024
caa22ca
Merge branch 'whatwg:main' into main
schenney-chromium Dec 18, 2024
488b95b
Fix Developer info
schenney-chromium Dec 18, 2024
01e6185
Merge branch 'whatwg:main' into main
schenney-chromium Jan 10, 2025
b6df5ee
Merge branch 'whatwg:main' into main
schenney-chromium Jan 22, 2025
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Post review revisions
schenney-chromium Jan 22, 2025
152e3a4
Clean up offscreen snapshot behavior
schenney-chromium Jan 23, 2025
60a5971
Fix the setter/getter for lang.
schenney-chromium Jan 23, 2025
720ff90
Next round of edits.
schenney-chromium Jan 23, 2025
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Original file line number Diff line number Diff line change
Expand Up @@ -65549,6 +65549,7 @@ interface mixin <dfn interface>CanvasPathDrawingStyles</dfn> {

interface mixin <dfn interface>CanvasTextDrawingStyles</dfn> {
// text
attribute DOMString <span data-x="dom-context-2d-lang">lang</span>; // (default: "inherit")
attribute DOMString <span data-x="dom-context-2d-font">font</span>; // (default 10px sans-serif)
attribute <span>CanvasTextAlign</span> <span data-x="dom-context-2d-textAlign">textAlign</span>; // (default: "start")
attribute <span>CanvasTextBaseline</span> <span data-x="dom-context-2d-textBaseline">textBaseline</span>; // (default: "alphabetic")
Expand Down Expand Up @@ -66022,6 +66023,7 @@ context.fillRect(100,0,50,50); // only this square remains</code></pre>
data-x="dom-context-2d-shadowOffsetX">shadowOffsetX</code>, <code
data-x="dom-context-2d-shadowOffsetY">shadowOffsetY</code>, <code
data-x="dom-context-2d-shadowBlur">shadowBlur</code>, <code
data-x="dom-context-2d-lang">lang</code>, <code
data-x="dom-context-2d-font">font</code>, <code
data-x="dom-context-2d-textAlign">textAlign</code>, <code
data-x="dom-context-2d-textBaseline">textBaseline</code>, <code
Expand Down Expand Up @@ -66516,13 +66518,26 @@ transform. ack Shaun Morris. -->
<h6>Text styles</h6>

<dl class="domintro">
<dt><code data-x=""><var>context</var>.<span subdfn data-x="dom-context-2d-lang">lang</span> [ = <var>value</var> ]</code></dt>
<dt><code data-x=""><var>styles</var>.<span data-x="dom-context-2d-lang">lang</span> [ = <var>value</var> ]</code></dt>
<dd>
<p>Returns the current language setting.</p>

<p>Can be set, to change the language used when resolving fonts. The syntax and valid values
are the same as those for the <span data-x="attr-lang">lang</span> element attribute, or the
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value "<code data-x="dom-context-2d-direction-inherit">inherit</code>" which is described
below.</p>

<p>The default is "<code data-x="dom-context-2d-direction-inherit">inherit</code>".</p>
</dd>

<dt><code data-x=""><var>context</var>.<span subdfn data-x="dom-context-2d-font">font</span> [ = <var>value</var> ]</code></dt>
<dt><code data-x=""><var>styles</var>.<span data-x="dom-context-2d-font">font</span> [ = <var>value</var> ]</code></dt>
<dd>
<p>Returns the current font settings.</p>

<p>Can be set, to change the font. The syntax is the same as for the CSS <span>'font'</span>
property; values that cannot be parsed as CSS font values are ignored.</p>
property; values that cannot be parsed as CSS font values are ignored. The default is "10px sans-serif".</p>

<p>Relative keywords and lengths are computed relative to the font of the <code>canvas</code>
element.</p>
Expand Down Expand Up @@ -66694,15 +66709,72 @@ worker.postMessage(offscreenCanvas, [offscreenCanvas]);</code></pre>
Notice that the font is only loaded inside the worker, and not in the document context.</p>
</div>

<p>The choice of fonts and glyphs within a font may vary according to the <dfn
attribute for="CanvasTextDrawingStyles"><code data-x="dom-context-2d-lang">lang</code></dfn>
IDL attribute. On setting, <code data-x="dom-context-2d-lang">lang</code> must be
a <span data-x="attr-lang">valid BCP 47 language tag</span> or the string "inherit".
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This doesn't actually define what the setter does.

I recommend looking at letterSpacing and wordSpacing. We want the same kind of language for lang and direction with the distinction between public API and internal state.

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Done, I think.

To determine the <dfn data-x="dom-context-2d-font-language">language for the font</dfn> from
the <code data-x="dom-context-2d-lang">lang</code> IDL attribute, use the following steps:</p>

<ol>
<li><p>If <var>object</var>'s <code data-x="dom-context-2d-lang">lang</code> value is
"inherit", then</p>
<ol>
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<li><p>If <var>object</var>'s <span>font style source object</span> is a <code>canvas</code>
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Couple issues here:

  1. "The lang getter steps are to return ..."
  2. It needs to return the value of some internal concept, similar to what letterSpacing does.
  3. It should probably be its own paragraph. We no longer really define getters and setters and concepts all in one paragraph.

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Done.

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I'm not sure I did "2" as you meant.

element, then set the <span data-x="dom-context-2d-font-language">language for the
font</span> to the element's <span data-x="language">language</span>. The <span
data-x="dom-context-2d-font-language">language for the font</span> must be updated when the
rendering context is created and each time the
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This needs to manipulate an internal concept.

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Not sure what you mean here. Has the last set of edits addressed this?

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No. If you look at the letterSpacing getter it is defined as follows:

The letterSpacing getter steps are to return the serialized form of this's letter spacing.

"letter spacing" there is the internal concept. That is what's missing here. The internal concept can have the same name as the getter, but it is distinct.

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I believe we're talking about the setter here. I feel I'm being slow, but is this sort of what you mean (sans links):

The lang setter steps are to set the value and update the internal font language

I think we agree that the value in lang is the string that round-trips, while the internal font language really is internal and not visible to authors.

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It's about both the getter and the setter. If the internal font language is the concept you could rewrite the getter as:

The language getter steps are to return this's internal font language.

(Note that you need to use "this" as well. We need to know where to find this internal concept after all.)

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The desired behavior for the getter relates to #10884. Do we want to return the "inherit" string or the internal font language? For direction Chromium and Webkit does the latter, while Firefox does the former.

From a back-compat position it's probably very hard to change direction, so maybe we should spec lang and direction to do the Chromium/WebKit thing. That's probably what developers most want. But it means no round-tripping.

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Since there is no interop, is there really a back-compat issue? Has Firefox received bug reports about this?
I am very interested in the results from your counters, but as a web-dev I was very surprised when you metionned Chrome and Safari's behavior for direction. I personnaly think it's bad to have the computed value instead of "inherit" there. We don't have a granular way of resetting the context's attributes, so I wouldn't be surprised someone made their own thing by just reading all the props on the context and setting them back later. Returning the computed value would break that.

For lang, as currently written, "inherit" does not update outside of the setter, because the value stored is computed in the setter itself. So in that case it would make sense to return the stored (computed) value, but I think "inherit" wouldn't be the proper keyword. If "inherit" really did update even after setting, then returning "inherit" would make more sense IMO.

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Since there is no interop, is there really a back-compat issue? Has Firefox received bug reports about this? I am very interested in the results from your counters, but as a web-dev I was very surprised when you metionned

It will take a couple of months to get counter information, as far as I can tell. I'm not sure what it can tell us about intent or desire, so I'll also try to find some hints from various developer forums (like how many people have asked about this issue, or asked how to get the direction or something like that).

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FWIW, per https://w3ctag.github.io/design-principles/#attributes-like-data, it should roundtrip, if it doesn't it should be, a setter method, and a getter method.

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Yeah I tend to agree with @Kaiido as to what we want here. It seems very strange to return the computed value, especially if it's informed by layout. (To be clear, I know how it all works, just speaking from the perspective of HTML standard semantics.)

<code data-x="dom-context-2d-lang">lang</code> attribute is
set to "inherit" (not on all changes to the element's <span
data-x="language">language</span>).</p></li>

<li><p>Otherwise, if <var>object</var>'s <span>font style source object</span> is an
<code>OffscreenCanvas</code> object created via <span
data-x="dom-canvas-transferControlToOffscreen">transferControlToOffscreen</span>,
then set the <span data-x="dom-context-2d-font-language">language for the font</span> to
the source canvas element's <span data-x="language">language</span>. The source
canvas's language should be snapshot at the time of transfer and the value used
whenever the <code data-x="dom-context-2d-lang">lang</code> value is "inherit".</p></li>
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<li>
<p>Otherwise, <var>object</var>'s <span>font style source object</span> is an
<code>OffscreenCanvas</code> object:</p>
<ol>
<li><p>Let <var>global</var> be <var>object</var>'s <span>relevant global
object</span>.</p></li>

<li><p>If <var>global</var> is a <code>Window</code> object, then set the <span
data-x="dom-context-2d-font-language">language for the font</span> to the
<span data-x="language">language</span> from <var>global</var>'s
<span data-x="concept-document-window">associated <code>Document</code></span>.
The <span data-x="concept-document-window">associated <code>Document</code></span>'s
language should be snapshot when the <code>OffscreenCanvas</code> is
created and the value used whenever the <code data-x="dom-context-2d-lang">lang</code>
value is "inherit".</p></li>

<li><p>Otherwise, the <span data-x="dom-context-2d-font-language">language for the
font</span> is explicitly unknown.</p></li>
</ol>
</li>
</ol>
<li><p>Otherwise, the <span data-x="dom-context-2d-font-language">language for the font</span> is the <code data-x="dom-context-2d-lang">lang</code> value.</p></li>
</ol>

<p>The <code data-x="dom-context-2d-lang">lang</code> IDL attribute, on getting, must return
the current value.</p>

<p>The <dfn attribute for="CanvasTextDrawingStyles"><code
data-x="dom-context-2d-font">font</code></dfn> IDL attribute, on setting, must be <span
data-x="parse something according to a CSS grammar">parsed as a CSS &lt;'font'> value</span> (but
without supporting property-independent style sheet syntax like 'inherit'), and the resulting font
must be assigned to the context, with the <span>'line-height'</span> component forced to 'normal',
with the <span>'font-size'</span> component converted to <span data-x="'px'">CSS pixels</span>,
and with system fonts being computed to explicit values. If the new value is syntactically
incorrect (including using property-independent style sheet syntax like 'inherit' or 'initial'),
then it must be ignored, without assigning a new font value. <ref>CSS</ref></p>
must be assigned to the context, with the <span data-x="dom-context-2d-font-language">language
for the font</span> as determined above, with the <span>'line-height'</span>
component forced to 'normal', with the <span>'font-size'</span> component converted to <span
data-x="'px'">CSS pixels</span>, and with system fonts being computed to explicit values. If the
new value is syntactically incorrect (including using property-independent style sheet syntax
like 'inherit' or 'initial'), then it must be ignored, without assigning a new font value.
<ref>CSS</ref></p>

<p>Font family names must be interpreted in the context of the <span>font style source
object</span> when the font is to be used; any fonts embedded using <code
Expand Down Expand Up @@ -66900,16 +66972,54 @@ worker.postMessage(offscreenCanvas, [offscreenCanvas]);</code></pre>

<dd><p>Treat input to the <span>text preparation algorithm</span> as right-to-left text.</p></dd>

<!--
<dt><dfn><code data-x="dom-context-2d-direction-auto">auto</code></dfn>
<dt><dfn enum-value for="CanvasDirection"><code data-x="dom-context-2d-direction-inherit">inherit</code></dfn>

<dd><p>Determine the direction from the input to the <span>text preparation algorithm</span>.</p></dd>
-->
<dd><p>Use the following process to determine the value for the
<dfn for="CanvasDirection"><code data-x="dom-context-2d-inherited-direction">inherited direction</code></dfn> referred to in the <span>text preparation algorithm</span></p>

<dt><dfn enum-value for="CanvasDirection"><code data-x="dom-context-2d-direction-inherit">inherit</code></dfn>
<ol>
<li><p>If <var>object</var>'s <span>font style source object</span> is a <code>canvas</code>
element:</p>

<ol>
<li><p>If the element has a <span>computed value</span> for
<span>'direction'</span> use that as the <span data-x="dom-context-2d-inherited-direction">inherited direction</span>.</p></li>

<li><p>Otherwise, use the <span data-x="the directionality">directionality</span>
of the element as the <span data-x="dom-context-2d-inherited-direction">inherited direction</span>.</p></li>
</ol>

<li>
<p>Otherwise, <var>object</var>'s <span>font style source object</span> is an
<code>OffscreenCanvas</code> object, set the
<span data-x="dom-context-2d-inherited-direction">inherited direction</span> when
the <code>OffscreenCanvas</code> is created and use the same value through the
life of the <code>OffscreenCanvas</code>:</p>

<ol>
<li><p>If the <code>OffscreenCanvas</code> was created via <span
data-x="dom-canvas-transferControlToOffscreen">transferControlToOffscreen</span>,
then set the <span data-x="dom-context-2d-inherited-direction">inherited direction
</span> to that of source canvas element's as described in the case above.</p></li>

<li><p>Otherwise, if <var>global</var> is a <code>Window</code> object:</p>
<ol>
<li><p>Let <var>Document</var> be the <var>global</var>'s
<span data-x="concept-document-window">associated <code>Document</code></span>.</p></li>

<dd><p>Default to the directionality of the <code>canvas</code> element or <code>Document</code>
as appropriate.</p></dd>
<li><p>Use the <span data-x="the directionality">directionality</span> of the
<var>Document</var> as the <span
data-x="dom-context-2d-inherited-direction">inherited direction</span>.</p></li>
</ol>
</li>

<li><p>Otherwise, set the <span
data-x="dom-context-2d-inherited-direction">inherited direction</span> to
"ltr".</p></li>
</ol>
</li>
</ol>
</dd>
</dl>

<p>The <code data-x="dom-context-2d-fontKerning">fontKerning</code> attribute's allowed keywords
Expand Down Expand Up @@ -67033,32 +67143,11 @@ worker.postMessage(offscreenCanvas, [offscreenCanvas]);</code></pre>
data-x="dom-context-2d-direction-rtl">rtl</code>"</dt>
<dd>Let <var>direction</var> be '<span data-x="concept-rtl">rtl</span>'.</dd>

<!--
<dt>If the <var>target</var> object's <code
data-x="dom-context-2d-direction">direction</code> attribute has the value "<code
data-x="dom-context-2d-direction-auto">auto</code>"</dt>
<dd>
Find the first character in <var>text</var> of bidirectional character type L, AL, or
R, if any. If such a character is found and it is of bidirectional character type AL or R,
then let <var>direction</var> be '<span data-x="concept-rtl">rtl</span>'; otherwise,
let <var>direction</var> be '<span data-x="concept-rtl">rtl</span>'. <ref>BIDI</ref>
</dd>
-->

<dt>If the <var>target</var> object's <span>font style source object</span> is an
element</dt>

<dd>Let <var>direction</var> be <span>the directionality</span> of the <var>target</var> object's <span>font style source object</span>.</dd>

<dt>If the <var>target</var> object's <span>font style source object</span> is a
<code>Document</code> with a non-null <span>document element</span></dt>

<dd>Let <var>direction</var> be <span>the directionality</span> of the <var>target</var>
object's <span>font style source object</span>'s <span>document element</span>.</dd>

<dt>Otherwise</dt>

<dd>Let <var>direction</var> be '<span data-x="concept-ltr">ltr</span>'.</dd>
data-x="dom-context-2d-direction-inherit">inherit</code>"</dt>
<dd>Let <var>direction</var> be the <var>target</var>'s <span
data-x="dom-context-2d-inherited-direction">inherited direction</span>.</dd>
</dl>
</li>

Expand Down Expand Up @@ -146999,6 +147088,7 @@ INSERT INTERFACES HERE
Ştefan Vargyas,
Stefan Weiss,
Steffen Meschkat,
Stephen Chenney,
Stephen Ma,
Stephen Stewart,
Stephen White,
Expand Down