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style: Add comments for the calculation of Procedure::Add on Scale and transform list.

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Add more comments to let people know the intention of the special case.

Differential Revision: https://phabricator.services.mozilla.com/D12070
This commit is contained in:
Boris Chiou 2018-11-16 19:06:16 +00:00 • committed by Emilio Cobos Álvarez
parent c81e1d82d5
commit 4f7a3ae533
1 changed files with 9 additions and 4 deletions
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13
components/style/values/animated/transform.rs
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@ -851,6 +851,10 @@ impl Animate for ComputedTransform {
fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
use std::borrow::Cow;
// Addition for transforms simply means appending to the list of
// transform functions. This is different to how we handle the other
// animation procedures so we treat it separately here rather than
// handling it in TransformOperation.
if procedure == Procedure::Add {
let result = self.0.iter().chain(&other.0).cloned().collect::<Vec<_>>();
return Ok(Transform(result));
@ -1584,8 +1588,10 @@ impl Animate for ComputedScale {
(&Scale::None, &Scale::None) => Ok(Scale::None),
(&Scale::Scale3D(_, ..), _) | (_, &Scale::Scale3D(_, ..)) => {
let (from, to) = (self.resolve(), other.resolve());
// FIXME(emilio, bug 1464791): why does this do something different than
// Scale3D / TransformOperation::Scale3D?
// For transform lists, we add by appending to the list of
// transform functions. However, ComputedScale cannot be
// simply concatenated, so we have to calculate the additive
// result here.
if procedure == Procedure::Add {
// scale(x1,y1,z1)*scale(x2,y2,z2) = scale(x1*x2, y1*y2, z1*z2)
return Ok(Scale::Scale3D(from.0 * to.0, from.1 * to.1, from.2 * to.2));
@ -1598,8 +1604,7 @@ impl Animate for ComputedScale {
},
(&Scale::Scale(_, ..), _) | (_, &Scale::Scale(_, ..)) => {
let (from, to) = (self.resolve(), other.resolve());
// FIXME(emilio, bug 1464791): why does this do something different than
// Scale / TransformOperation::Scale?
// As with Scale3D, addition needs special handling.
if procedure == Procedure::Add {
// scale(x1,y1)*scale(x2,y2) = scale(x1*x2, y1*y2)
return Ok(Scale::Scale(from.0 * to.0, from.1 * to.1));