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style: Tweak the serialization of rotate property

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The serialization of rotate should be updated to match the current spec.

1. If a rotation about the z axis (that is, in 2D) is specified, the property
   must serialize as just an <angle>.

2. If any other rotation is specified, the property must serialize with an axis
   specified. If the axis is parallel with the x or y axes, it must serialize
   as the appropriate keyword.

Also, we need to handle the zero length vector separately because it is
parallel to every other vector but different from x axis, y axis, or z axis.

Differential Revision: https://phabricator.services.mozilla.com/D127747
This commit is contained in:
Boris Chiou 2023-05-27 16:19:05 +02:00 • committed by Oriol Brufau
parent 6899931303
commit f00818b8ec
1 changed files with 30 additions and 14 deletions
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44
components/style/values/generics/transform.rs
View file

@ -687,7 +687,7 @@ pub trait IsParallelTo {
impl<Number, Angle> ToCss for Rotate<Number, Angle>
where
Number: Copy + ToCss,
Number: Copy + ToCss + Zero,
Angle: ToCss,
(Number, Number, Number): IsParallelTo,
{
@ -700,25 +700,41 @@ where
Rotate::None => dest.write_str("none"),
Rotate::Rotate(ref angle) => angle.to_css(dest),
Rotate::Rotate3D(x, y, z, ref angle) => {
// If a 3d rotation is specified, the property must serialize with an axis
// specified. If the axis is parallel with the x, y, or z axises, it must
// serialize as the appropriate keyword.
// If the axis is parallel with the x or y axes, it must serialize as the
// appropriate keyword. If a rotation about the z axis (that is, in 2D) is
// specified, the property must serialize as just an <angle>
//
// https://drafts.csswg.org/css-transforms-2/#individual-transform-serialization
let v = (x, y, z);
if v.is_parallel_to(&DirectionVector::new(1., 0., 0.)) {
dest.write_char('x')?;
let axis = if x.is_zero() && y.is_zero() && z.is_zero() {
// The zero length vector is parallel to every other vector, so
// is_parallel_to() returns true for it. However, it is definitely different
// from x axis, y axis, or z axis, and it's meaningless to perform a rotation
// using that direction vector. So we *have* to serialize it using that same
// vector - we can't simplify to some theoretically parallel axis-aligned
// vector.
None
} else if v.is_parallel_to(&DirectionVector::new(1., 0., 0.)) {
Some("x ")
} else if v.is_parallel_to(&DirectionVector::new(0., 1., 0.)) {
dest.write_char('y')?;
Some("y ")
} else if v.is_parallel_to(&DirectionVector::new(0., 0., 1.)) {
dest.write_char('z')?;
// When we're parallel to the z-axis, we can just serialize the angle.
return angle.to_css(dest);
} else {
x.to_css(dest)?;
dest.write_char(' ')?;
y.to_css(dest)?;
dest.write_char(' ')?;
z.to_css(dest)?;
None
};
match axis {
Some(a) => dest.write_str(a)?,
None => {
x.to_css(dest)?;
dest.write_char(' ')?;
y.to_css(dest)?;
dest.write_char(' ')?;
z.to_css(dest)?;
dest.write_char(' ')?;
}
}
dest.write_char(' ')?;
angle.to_css(dest)
},
}