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Re: [css-masking] 'mask' with resource and image references (was: [css4-images] support for SVG Paint Servers without element())

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Wed, 7 Nov 2012 13:08:43 -0800
Message-ID: <CAAWBYDCBibDX6NsMB35cQ_3D8E_VZ9-vff+R_VPvTGyVLm0fhw@mail.gmail.com>
To: Dirk Schulze <dschulze@adobe.com>
Cc: "robert@ocallahan.org" <robert@ocallahan.org>, "www-style@w3.org list" <www-style@w3.org>
On Wed, Nov 7, 2012 at 12:45 PM, Dirk Schulze <dschulze@adobe.com> wrote:
> On Nov 7, 2012, at 10:43 AM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
>> So, 'mask-image' needs to have its grammar revised to take this into
>> account, so that it can take mask references as well.
>
> This would be the consequence, but wouldn't help IMO.
>
> mask-image: url(image#frag);
>
> It would be unclear until the processing, if this is an SVG resource or an image. However, the syntax would be valid in both cases. The problem for WebKit is, that we already assume that this will be an CSS Image and already start creating an CSSImage resource. This is incompatible with an SVG resource (because of various reasons roc already mentioned). That's why this is not an option for WebKit right now.

Let's be precise here.  It's unclear at parse time whether you're
pointing at a <mask> element or some other paint server element like
<linearGradient>.  You *do* know, at parse time, that it won't be
loading the SVG as an image, because 'mask' is on the list of
properties that default frag-urls to being a resource reference rather
than an image.

Now, a paint server *is* a CSS <image> value, but our existing code
obviously doesn't do anything special with this yet.  (Our existing
code for mask-image doesn't implement roc's rule, so it'll currently
try and interpret it as an SVG image, likely an SVG Stack.)  Once we
switch over, though, we should be fine - we can generate a mask from
the paint server (turned into an image) or the <mask> element equally
well at that point, right?


>> Alternately, we
>> need an additional property which takes a mask ref, and overrides
>> mask-image if specified (like list-style-type and list-style-image -
>> the latter wins if it's not none).
>
> This additional property would make sense from the logical point of view and seem to solve the issue described above, but doesn't help at all on the short hand:
>
> mask: url(image#frag);
>
> Is that 'mask-image'? 'mask-reference'? You can't say until you load the resource. So you can't distinguish between the both during the pure parsing process. This seems to be worst IMO.
>
> Another name for the shorthand for the 'mask-*' properties on the other hand would work for all browsers.

Having 'mask' be a longhand property and some 'mask-*' property be the
shorthand would be *terrible* for usability.  We should avoid this if
there is any possibility of solving this in a different way.

~TJ
Received on Wednesday, 7 November 2012 21:09:31 GMT

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