[css-view-transitions-1] Clarify that observable image size refers to…

… the border-box, and observed natural size is not affected by hw constraints (#8819)

* Clarify that observable image size refers to the border-box

Ink-overflow is an implementation detail, and up to the UA
to apply. object-view-box doesn't directly affect the ink-overflow rect.

See [resolution](#8597 (comment)).

Closes #8597

* Fix regarding texture size

* Add changelog entries

* Apply nits

* clarify note

css-view-transitions-1/Overview.bs

@@ -1570,10 +1570,10 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;
  over an infinite transparent canvas,
  following the [=capture rendering characteristics=].
 
- 1. Let |interestRectangle| be the result of [=computing the interest rectangle=] for |element|.
+ 1. Return the portion of the canvas that includes |element|'s [=ink overflow rectangle=] as an image.
+ The [=natural size=] of the image must be |element|'s [=border box=]'s [=size=],
+ and its origin corresponds to the |element|'s [=border box=]'s origin.
 
- 1. Return the portion of the canvas within |interestRectangle| as an image.
- The natural size of the image is equal to the |interestRectangle| bounds.
  </div>
 
 ### [=Capture rendering characteristics=] ### {#capture-rendering-characteristics-algorithm}
@@ -1590,6 +1590,10 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;
 
  * Effects on the element, such as 'opacity' and 'filter' are applied to the capture.
 
+ * Implementations may clip the rendered contents if the [=ink overflow rectangle=] exceeds some [=implementation-defined=] maximum.
+ However, the captured image should include, at the very least, the contents of |element| that intersect with the [=snapshot root=].
+ Implementations may adjust the rasterization quality to account for elements with a large [=ink overflow area=] that are transformed into view.
+
  * [=list/For each=] |descendant| of [=shadow-including descendant=] {{Element}} and [=pseudo-element=] of |element|,
  if |descendant| has a [=computed value=] of 'view-transition-name' that is not ''view-transition-name/none'',
  then skip painting |descendant|.
@@ -1601,28 +1605,6 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;
  Issue: Specify what happens with 'mix-blend-mode'.
  </div>
 
-### [=Compute the interest rectangle=] ### {#compute-the-interest-rectangle-algorithm}
-
- <div algorithm>
- To <dfn lt="computing the interest rectangle|compute the interest rectangle">compute the interest rectangle</dfn> of an {{Element}} |element|, perform the following steps.
- They return a rectangle.
-
- Note: The interest rectangle is the subset of |element|'s [=ink overflow rectangle=] that should be captured.
- This is required for cases where an element's ink overflow rectangle needs to be clipped because of hardware constraints.
- For example, if it exceeds the maximum texture size.
-
- 1. Assert: |element| is not |element|'s [=node document=]'s [=document element=].
-
- Note: The [=document element=] is captured differently, as specified in [=capture the image=].
-
- 1. If |element|'s [=ink overflow area=] does not exceed an implementation-defined maximum size,
- then return a rectangle that is equal to |element|'s [=ink overflow rectangle=].
-
- 1. Otherwise:
-
- Issue: Define the algorithm used to clip the snapshot when it exceeds max size.
- </div>
-
 ## [=Handle transition frame=] ## {#handle-transition-frame-algorithm}
 
  <div algorithm>
@@ -1810,6 +1792,8 @@ Changes from <a href="https://www.w3.org/TR/2022/WD-css-view-transitions-1-20221
 * Add support for :only-child. See <a href="https://github.com/w3c/csswg-drafts/issues/8057">issue 8057</a>.
 * Add concept of a tree of pseudo-elements under [=pseudo-element root=]. See <a href="https://github.com/w3c/csswg-drafts/issues/8113">issue 8113</a>.
 * When skipping a transition, the {{UpdateCallback}} is called in own task rather than synchronosly. See <a href="https://github.com/w3c/csswg-drafts/issues/7904">issue 7904</a>
+* When capturing images, at least the in-viewport part of the image should be captured, downscale if needed. See <a href="https://github.com/w3c/csswg-drafts/issues/8561">issue 8561</a>.
+* Applying the [=ink overflow=] to the captured image is implementation defined, and doesn't affect the image's [=natural size=]. See <a href="https://github.com/w3c/csswg-drafts/issues/8597">issue 8597</a>.
 
 <h3 id="changes-since-2022-10-25">
 Changes from <a href="https://www.w3.org/TR/2022/WD-css-view-transitions-1-20221025/">2022-10-25 Working Draft (FPWD)</a>