[webkit-dev] webkit-resource: referring to resources in User Agent stylesheet

[Dimitri Glazkov]

It would be extremely easy to limit it to UA sheets only.

:DG<

On Tue, Apr 26, 2011 at 2:05 PM, Sam Weinig <weinig at apple.com> wrote:
> Would we want this to be web facing? Or should we limit it to inside the built-in stylesheets?
>
> -Sam
>
> On Apr 26, 2011, at 1:18 PM, Dimitri Glazkov wrote:
>
>> Hello,
>>
>> SUMMARY: we would like to introduce a "webkit-resource" URL scheme for
>> CSS, which would refer to images baked into WebKit.
>>
>> BACKGROUND: in order to style media controls today, we rely on the
>> ControlPart enum
>> (http://codesearch.google.com/codesearch/p#OAMlx_jo-ck/src/third_party/WebKit/Source/WebCore/platform/ThemeTypes.h&l=48&exact_package=chromium),
>> which is exposed as the  -webkit-appearance CSS attribute. For
>> example:
>>
>> video::-webkit-media-controls-play-button {
>>  -webkit-appearance: media-play-button;
>> }
>>
>> In addition, the state of the button is further adjusted by looking at
>> the runtime state or media characteristics of the element (is the user
>> currently hovering or clicking on the element? is it playing? is it
>> streaming? has an error occurred?). This happens at the port layer, in
>> RenderTheme implementation.
>>
>> With impending introduction of media element pseudo-classes and the
>> patch in bug 58342 landing, we will be able to sense these extra
>> states at the CSS level:
>>
>> video:playing::-webkit-media-controls-play-button:hover {
>>  -webkit-appearance: media-play-button-playing-hover;
>> }
>>
>> This would result in a lot less of mindless style-flipping
>> RenderTheme/MediaControlElement code and provide more flexibility for
>> each port to design their pretty things.
>>
>> However, sticking with existing -webkit-appearance strategy will
>> result in ControlPart enum exploding as combinatorial math suggests.
>> Which is a ...
>>
>> PROBLEM: We need a way to somehow in CSS associate an element state
>> with a relatively arbitrary key to avoid ControlPart from becoming the
>> tallest enum ever.
>>
>> SOLUTION: Looking at the current media controls implementations, most
>> of the -webkit-appearance states are kind of like background images,
>> each reflecting appearance of an element at a particular state. Thus,
>> it seems we should be able to solve this by just using CSS
>> backgrounds:
>>
>> video:playing::-webkit-media-controls-play-button:hover {
>>   background: url(/media-controls/play-button-hover.png);
>> }
>>
>> That is how the authors would style the media controls. However, at
>> the UA level, we shouldn't probably be loading resources from random
>> sites. Instead, we need a way to bake these images into the WebKit
>> runtime, and then a way to refer to them from the stylesheet.
>>
>> This is where a vendor-specific URL scheme comes in:
>>
>> video:playing::-webkit-media-controls-play-button:hover {
>>   background: url(webkit-resource:/media-controls/play-button-hover.png);
>> }
>>
>> A quick poll of smart people (abarth and smfr) seems to indicate it's
>> not a completely horrid idea.
>>
>> WDYT? Thoughts? Comments?
>>
>> :DG<
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>
>