style/values/computed/
position.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5//! CSS handling for the computed value of
6//! [`position`][position] values.
7//!
8//! [position]: https://drafts.csswg.org/css-backgrounds-3/#position
9
10use crate::logical_geometry::PhysicalSide;
11use crate::values::computed::{
12    Context, Integer, LengthPercentage, NonNegativeNumber, Percentage, ToComputedValue,
13};
14use crate::values::generics;
15use crate::values::generics::position::{
16    AnchorSideKeyword, AspectRatio as GenericAspectRatio, GenericAnchorFunction, GenericAnchorSide,
17    GenericInset, Position as GenericPosition, PositionComponent as GenericPositionComponent,
18    PositionOrAuto as GenericPositionOrAuto, ZIndex as GenericZIndex,
19};
20pub use crate::values::specified::position::{
21    AnchorName, AnchorScope, DashedIdentAndOrTryTactic, GridAutoFlow, GridTemplateAreas,
22    MasonryAutoFlow, PositionAnchor, PositionArea, PositionAreaAxis, PositionAreaKeyword,
23    PositionAreaType, PositionTryFallbacks, PositionTryFallbacksTryTactic,
24    PositionTryFallbacksTryTacticKeyword, PositionTryOrder, PositionVisibility,
25};
26use crate::Zero;
27use std::fmt::{self, Write};
28use style_traits::{CssWriter, ToCss};
29
30/// The computed value of a CSS `<position>`
31pub type Position = GenericPosition<HorizontalPosition, VerticalPosition>;
32
33/// The computed value of an `auto | <position>`
34pub type PositionOrAuto = GenericPositionOrAuto<Position>;
35
36/// The computed value of a CSS horizontal position.
37pub type HorizontalPosition = LengthPercentage;
38
39/// The computed value of a CSS vertical position.
40pub type VerticalPosition = LengthPercentage;
41
42/// The computed value of anchor side.
43pub type AnchorSide = GenericAnchorSide<Percentage>;
44
45impl AnchorSide {
46    /// Break down given anchor side into its equivalent keyword and percentage.
47    pub fn keyword_and_percentage(&self) -> (AnchorSideKeyword, Percentage) {
48        match self {
49            Self::Percentage(p) => (AnchorSideKeyword::Start, *p),
50            Self::Keyword(k) => {
51                if matches!(k, AnchorSideKeyword::Center) {
52                    (AnchorSideKeyword::Start, Percentage(0.5))
53                } else {
54                    (*k, Percentage::zero())
55                }
56            },
57        }
58    }
59}
60
61/// The computed value of an `anchor()` function.
62pub type AnchorFunction = GenericAnchorFunction<Percentage, Inset>;
63
64#[cfg(feature = "gecko")]
65use crate::{
66    gecko_bindings::structs::AnchorPosOffsetResolutionParams,
67    values::{computed::Length, DashedIdent},
68};
69
70impl AnchorFunction {
71    /// Resolve the anchor function with the given resolver. Returns `Err()` if no anchor is found.
72    #[cfg(feature = "gecko")]
73    pub fn resolve(
74        anchor_name: &DashedIdent,
75        anchor_side: &AnchorSide,
76        prop_side: PhysicalSide,
77        params: &AnchorPosOffsetResolutionParams,
78    ) -> Result<Length, ()> {
79        use crate::gecko_bindings::structs::Gecko_GetAnchorPosOffset;
80
81        let (keyword, percentage) = anchor_side.keyword_and_percentage();
82        let mut offset = Length::zero();
83        let valid = unsafe {
84            Gecko_GetAnchorPosOffset(
85                params,
86                anchor_name.0.as_ptr(),
87                prop_side as u8,
88                keyword as u8,
89                percentage.0,
90                &mut offset,
91            )
92        };
93
94        if !valid {
95            return Err(());
96        }
97
98        Ok(offset)
99    }
100}
101
102/// Perform the adjustment of a given value for a given try tactic, as per:
103/// https://drafts.csswg.org/css-anchor-position-1/#swap-due-to-a-try-tactic
104pub(crate) trait TryTacticAdjustment {
105    /// Performs the adjustments necessary given an old side we're relative to, and a new side
106    /// we're relative to.
107    fn try_tactic_adjustment(&mut self, old_side: PhysicalSide, new_side: PhysicalSide);
108}
109
110impl<T: TryTacticAdjustment> TryTacticAdjustment for Box<T> {
111    fn try_tactic_adjustment(&mut self, old_side: PhysicalSide, new_side: PhysicalSide) {
112        (**self).try_tactic_adjustment(old_side, new_side);
113    }
114}
115
116impl<T: TryTacticAdjustment> TryTacticAdjustment for generics::NonNegative<T> {
117    fn try_tactic_adjustment(&mut self, old_side: PhysicalSide, new_side: PhysicalSide) {
118        self.0.try_tactic_adjustment(old_side, new_side);
119    }
120}
121
122impl<Percentage: TryTacticAdjustment> TryTacticAdjustment for GenericAnchorSide<Percentage> {
123    fn try_tactic_adjustment(&mut self, old_side: PhysicalSide, new_side: PhysicalSide) {
124        match self {
125            Self::Percentage(p) => p.try_tactic_adjustment(old_side, new_side),
126            Self::Keyword(side) => side.try_tactic_adjustment(old_side, new_side),
127        }
128    }
129}
130
131impl<Percentage: TryTacticAdjustment, Fallback: TryTacticAdjustment> TryTacticAdjustment
132    for GenericAnchorFunction<Percentage, Fallback>
133{
134    fn try_tactic_adjustment(&mut self, old_side: PhysicalSide, new_side: PhysicalSide) {
135        self.side.try_tactic_adjustment(old_side, new_side);
136        if let Some(fallback) = self.fallback.as_mut() {
137            fallback.try_tactic_adjustment(old_side, new_side);
138        }
139    }
140}
141
142/// A computed type for `inset` properties.
143pub type Inset = GenericInset<Percentage, LengthPercentage>;
144impl TryTacticAdjustment for Inset {
145    // https://drafts.csswg.org/css-anchor-position-1/#swap-due-to-a-try-tactic:
146    //
147    //     For inset properties, change the specified side in anchor() functions to maintain the
148    //     same relative relationship to the new direction that they had to the old.
149    //
150    //     If a <percentage> is used, and directions are opposing, change it to 100% minus the
151    //     original percentage.
152    fn try_tactic_adjustment(&mut self, old_side: PhysicalSide, new_side: PhysicalSide) {
153        match self {
154            Self::Auto => {},
155            Self::AnchorContainingCalcFunction(lp) | Self::LengthPercentage(lp) => {
156                lp.try_tactic_adjustment(old_side, new_side)
157            },
158            Self::AnchorFunction(anchor) => anchor.try_tactic_adjustment(old_side, new_side),
159            Self::AnchorSizeFunction(anchor) => anchor.try_tactic_adjustment(old_side, new_side),
160        }
161    }
162}
163
164impl Position {
165    /// `50% 50%`
166    #[inline]
167    pub fn center() -> Self {
168        Self::new(
169            LengthPercentage::new_percent(Percentage(0.5)),
170            LengthPercentage::new_percent(Percentage(0.5)),
171        )
172    }
173
174    /// `0% 0%`
175    #[inline]
176    pub fn zero() -> Self {
177        Self::new(LengthPercentage::zero(), LengthPercentage::zero())
178    }
179}
180
181impl ToCss for Position {
182    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
183    where
184        W: Write,
185    {
186        self.horizontal.to_css(dest)?;
187        dest.write_char(' ')?;
188        self.vertical.to_css(dest)
189    }
190}
191
192impl GenericPositionComponent for LengthPercentage {
193    fn is_center(&self) -> bool {
194        match self.to_percentage() {
195            Some(Percentage(per)) => per == 0.5,
196            _ => false,
197        }
198    }
199}
200
201#[inline]
202fn block_or_inline_to_inferred(keyword: PositionAreaKeyword) -> PositionAreaKeyword {
203    if matches!(
204        keyword.axis(),
205        PositionAreaAxis::Block | PositionAreaAxis::Inline
206    ) {
207        keyword.with_axis(PositionAreaAxis::Inferred)
208    } else {
209        keyword
210    }
211}
212
213#[inline]
214fn inferred_to_block(keyword: PositionAreaKeyword) -> PositionAreaKeyword {
215    keyword.with_inferred_axis(PositionAreaAxis::Block)
216}
217
218#[inline]
219fn inferred_to_inline(keyword: PositionAreaKeyword) -> PositionAreaKeyword {
220    keyword.with_inferred_axis(PositionAreaAxis::Inline)
221}
222
223// This exists because the spec currently says that further simplifications
224// should be made to the computed value. That's confusing though, and probably
225// all these simplifications should be wrapped up into the simplifications that
226// we make to the specified value. I.e. all this should happen in
227// PositionArea::parse_internal().
228// See also https://github.com/w3c/csswg-drafts/issues/12759
229impl ToComputedValue for PositionArea {
230    type ComputedValue = Self;
231
232    fn to_computed_value(&self, _context: &Context) -> Self {
233        let mut computed = self.clone();
234        let pair_type = self.get_type();
235        if pair_type == PositionAreaType::Logical || pair_type == PositionAreaType::SelfLogical {
236            if computed.second != PositionAreaKeyword::None {
237                computed.first = block_or_inline_to_inferred(computed.first);
238                computed.second = block_or_inline_to_inferred(computed.second);
239            }
240        } else if pair_type == PositionAreaType::Inferred
241            || pair_type == PositionAreaType::SelfInferred
242        {
243            if computed.second == PositionAreaKeyword::SpanAll {
244                // We remove the superfluous span-all, converting the inferred
245                // keyword to a logical keyword to avoid ambiguity, per spec.
246                computed.first = inferred_to_block(computed.first);
247                computed.second = PositionAreaKeyword::None;
248            } else if computed.first == PositionAreaKeyword::SpanAll {
249                computed.first = computed.second;
250                computed.first = inferred_to_inline(computed.first);
251                computed.second = PositionAreaKeyword::None;
252            }
253        }
254
255        if computed.first == computed.second {
256            computed.second = PositionAreaKeyword::None;
257        }
258        computed
259    }
260
261    fn from_computed_value(computed: &Self) -> Self {
262        computed.clone()
263    }
264}
265
266/// A computed value for the `z-index` property.
267pub type ZIndex = GenericZIndex<Integer>;
268
269/// A computed value for the `aspect-ratio` property.
270pub type AspectRatio = GenericAspectRatio<NonNegativeNumber>;
style/values/computed/position.rs

style/values/computed/
position.rs
