SMIL:CSS Animation: Difference between revisions
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=== Implementing <code>getOverrideStyle()</code> === | === Implementing <code>getOverrideStyle()</code> === | ||
Note that Gecko doesn't currently implement <code>getOverrideStyle()</code>. Here's a basic outline of how | Note that Gecko doesn't currently implement <code>getOverrideStyle()</code>. Here's a basic outline of how this function could be implemented (& is implemeted in the patch linked above): | ||
* Add a new <code>nsRefPtr<nsDOMCSSDeclaration> mOverrideStyle</code> member variable on each <code>nsStyledElement</code>, to be used as a backing store for that element's override style. | |||
* I've based the implementation of this largely on the content style rule in SVG. (See <code>mContentStyleRule</code> in [http://mxr.mozilla.org/seamonkey/source/content/svg/content/src/nsSVGElement.h nsSVGElement.h] and [http://mxr.mozilla.org/seamonkey/source/content/svg/content/src/nsSVGElement.cpp nsSVGElement.cpp] ) | |||
* The override style is queryable (& editable) via a new method <code>nsIContent::GetOverrideStyle</code>. By default, this method has an empty implementation, but <code>nsStyledElement</code> overrides this method to return its <code>mOverrideStyle</code>. | |||
* The override style rule is read (& applied) in HTMLCSSStyleSheetImpl::RulesMatching, right after we read the inline style rule. | |||
* See [http://hg.mozilla.org/users/dholbert_mozilla.com/smil-patches/file/tip/getoverridestyle.patch patch] for more details (it's fairly small) | |||
Latest revision as of 13:46, 20 March 2009
Current status
There's an existing smil_css patch in dholbert's smil-patches patch-queue. This patch applies on top of the other patches in the queue, and it makes use of a simple "getOverrideStyle" implementation in order to set styles.
The smil_css patch is not complete yet -- it currently has these limitations:
- It can only animate CSS properties of type
nsCSSValue. (notnsCSSValuePair/nsCSSValueRect/ etc) - It can only currently interpolate between fixed-length units. (inch, mm, pt, etc). (unit-conversion code needs a reference to the PresContext & font-metrics to interpolate/interconvert between fixed-length units / display pixels / em-units / ex-units.)
Overview of Proposed Strategy
Animating CSS Style
As suggested in the documentation on the "SMIL Sandwich Model" in the smil-animation spec, I'm proposing that we use an implementation backed by getOverrideStyle().
Here's an overview of the steps required to animate a specific CSS property on a specific element, using getOverrideStyle(), during a SMIL animation sample:
- Call
getOverrideStyle()on the element, and from this, clear any existing value for the CSS property in question. (This ensures thatgetComputedStyle()won't reflect any animation effects, so it can be used as a 'base value' for animation in the next step) - Perform SMIL interpolation & compositing for the CSS property, using
getComputedStyle()as the base value. - Store the final composited value of the property in
getOverrideStyle().
Implementing getOverrideStyle()
Note that Gecko doesn't currently implement getOverrideStyle(). Here's a basic outline of how this function could be implemented (& is implemeted in the patch linked above):
- Add a new
nsRefPtr<nsDOMCSSDeclaration> mOverrideStylemember variable on eachnsStyledElement, to be used as a backing store for that element's override style. - I've based the implementation of this largely on the content style rule in SVG. (See
mContentStyleRulein nsSVGElement.h and nsSVGElement.cpp ) - The override style is queryable (& editable) via a new method
nsIContent::GetOverrideStyle. By default, this method has an empty implementation, butnsStyledElementoverrides this method to return itsmOverrideStyle. - The override style rule is read (& applied) in HTMLCSSStyleSheetImpl::RulesMatching, right after we read the inline style rule.
- See patch for more details (it's fairly small)