replaced.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

use crate::dom_traversal::NodeExt;
use crate::fragments::{Fragment, ImageFragment};
use crate::geom::flow_relative::{Rect, Vec2};
use crate::geom::physical;
use crate::sizing::ContentSizes;
use crate::style_ext::ComputedValuesExt;
use crate::ContainingBlock;
use net_traits::image::base::Image;
use servo_arc::Arc as ServoArc;
use std::sync::Arc;
use style::properties::ComputedValues;
use style::values::computed::{Length, LengthOrAuto};
use style::values::CSSFloat;
use style::Zero;

#[derive(Debug)]
pub(crate) struct ReplacedContent {
    pub kind: ReplacedContentKind,
    intrinsic: IntrinsicSizes,
}

/// * Raster images always have an instrinsic width and height, with 1 image pixel = 1px.
///   The intrinsic ratio should be based on dividing those.
///   See https://github.com/w3c/csswg-drafts/issues/4572 for the case where either is zero.
///   PNG specifically disallows this but I (SimonSapin) am not sure about other formats.
///
/// * Form controls have both intrinsic width and height **but no intrinsic ratio**.
///   See https://github.com/w3c/csswg-drafts/issues/1044 and
///   https://drafts.csswg.org/css-images/#intrinsic-dimensions “In general, […]”
///
/// * For SVG, see https://svgwg.org/svg2-draft/coords.html#SizingSVGInCSS
///   and again https://github.com/w3c/csswg-drafts/issues/4572.
#[derive(Debug)]
pub(crate) struct IntrinsicSizes {
    pub width: Option<Length>,
    pub height: Option<Length>,
    pub ratio: Option<CSSFloat>,
}

#[derive(Debug)]
pub(crate) enum ReplacedContentKind {
    Image(Option<Arc<Image>>),
}

impl ReplacedContent {
    pub fn for_element<'dom>(element: impl NodeExt<'dom>) -> Option<Self> {
        if let Some((image, intrinsic_size_in_dots)) = element.as_image() {
            // FIXME: should 'image-resolution' (when implemented) be used *instead* of
            // `script::dom::htmlimageelement::ImageRequest::current_pixel_density`?

            // https://drafts.csswg.org/css-images-4/#the-image-resolution
            let dppx = 1.0;

            let width = (intrinsic_size_in_dots.x as CSSFloat) / dppx;
            let height = (intrinsic_size_in_dots.y as CSSFloat) / dppx;
            return Some(Self {
                kind: ReplacedContentKind::Image(image),
                intrinsic: IntrinsicSizes {
                    width: Some(Length::new(width)),
                    height: Some(Length::new(height)),
                    // FIXME https://github.com/w3c/csswg-drafts/issues/4572
                    ratio: Some(width / height),
                },
            });
        }
        None
    }

    fn flow_relative_intrinsic_size(&self, style: &ComputedValues) -> Vec2<Option<Length>> {
        let intrinsic_size = physical::Vec2 {
            x: self.intrinsic.width,
            y: self.intrinsic.height,
        };
        intrinsic_size.size_to_flow_relative(style.writing_mode)
    }

    fn inline_size_over_block_size_intrinsic_ratio(
        &self,
        style: &ComputedValues,
    ) -> Option<CSSFloat> {
        self.intrinsic.ratio.map(|width_over_height| {
            if style.writing_mode.is_vertical() {
                1. / width_over_height
            } else {
                width_over_height
            }
        })
    }

    pub fn inline_content_sizes(&self, style: &ComputedValues) -> ContentSizes {
        // FIXME: min/max-content of replaced elements is not defined in
        // https://dbaron.org/css/intrinsic/
        // This seems sensible?
        let inline = self
            .flow_relative_intrinsic_size(style)
            .inline
            .unwrap_or(Length::zero());
        ContentSizes {
            min_content: inline,
            max_content: inline,
        }
    }

    pub fn make_fragments<'a>(
        &'a self,
        style: &ServoArc<ComputedValues>,
        size: Vec2<Length>,
    ) -> Vec<Fragment> {
        match &self.kind {
            ReplacedContentKind::Image(image) => image
                .as_ref()
                .and_then(|image| image.id)
                .map(|image_key| {
                    Fragment::Image(ImageFragment {
                        style: style.clone(),
                        rect: Rect {
                            start_corner: Vec2::zero(),
                            size,
                        },
                        image_key,
                    })
                })
                .into_iter()
                .collect(),
        }
    }

    /// https://drafts.csswg.org/css2/visudet.html#inline-replaced-width
    /// https://drafts.csswg.org/css2/visudet.html#inline-replaced-height
    ///
    /// Also used in other cases, for example
    /// https://drafts.csswg.org/css2/visudet.html#block-replaced-width
    pub fn used_size_as_if_inline_element(
        &self,
        containing_block: &ContainingBlock,
        style: &ComputedValues,
    ) -> Vec2<Length> {
        let mode = style.writing_mode;
        let intrinsic_size = self.flow_relative_intrinsic_size(style);
        let intrinsic_ratio = self.inline_size_over_block_size_intrinsic_ratio(style);

        let box_size = style.box_size().percentages_relative_to(containing_block);
        let min_box_size = style
            .min_box_size()
            .percentages_relative_to(containing_block)
            .auto_is(Length::zero);
        let max_box_size = style
            .max_box_size()
            .percentages_relative_to(containing_block);

        let default_object_size = || {
            // FIXME:
            // “If 300px is too wide to fit the device, UAs should use the width of
            //  the largest rectangle that has a 2:1 ratio and fits the device instead.”
            // “height of the largest rectangle that has a 2:1 ratio, has a height not greater
            //  than 150px, and has a width not greater than the device width.”
            physical::Vec2 {
                x: Length::new(300.),
                y: Length::new(150.),
            }
            .size_to_flow_relative(mode)
        };
        let clamp = |inline_size: Length, block_size: Length| Vec2 {
            inline: inline_size.clamp_between_extremums(min_box_size.inline, max_box_size.inline),
            block: block_size.clamp_between_extremums(min_box_size.block, max_box_size.block),
        };
        // https://drafts.csswg.org/css2/visudet.html#min-max-widths
        // https://drafts.csswg.org/css2/visudet.html#min-max-heights
        match (box_size.inline, box_size.block) {
            (LengthOrAuto::LengthPercentage(inline), LengthOrAuto::LengthPercentage(block)) => {
                clamp(inline, block)
            },
            (LengthOrAuto::LengthPercentage(inline), LengthOrAuto::Auto) => {
                let block = if let Some(i_over_b) = intrinsic_ratio {
                    inline / i_over_b
                } else if let Some(block) = intrinsic_size.block {
                    block
                } else {
                    default_object_size().block
                };
                clamp(inline, block)
            },
            (LengthOrAuto::Auto, LengthOrAuto::LengthPercentage(block)) => {
                let inline = if let Some(i_over_b) = intrinsic_ratio {
                    block * i_over_b
                } else if let Some(inline) = intrinsic_size.inline {
                    inline
                } else {
                    default_object_size().inline
                };
                clamp(inline, block)
            },
            (LengthOrAuto::Auto, LengthOrAuto::Auto) => {
                let inline_size =
                    match (intrinsic_size.inline, intrinsic_size.block, intrinsic_ratio) {
                        (Some(inline), _, _) => inline,
                        (None, Some(block), Some(i_over_b)) => {
                            // “used height” in CSS 2 is always gonna be the intrinsic one,
                            // since it is available.
                            block * i_over_b
                        },
                        // FIXME
                        //
                        // “If 'height' and 'width' both have computed values of 'auto'
                        // and the element has an intrinsic ratio but no intrinsic height or width,
                        // […]”
                        //
                        // In this `match` expression this would be an additional arm here:
                        //
                        // ```
                        // (Vec2 { inline: None, block: None }, Some(_)) => {…}
                        // ```
                        //
                        // “[…] then the used value of 'width' is undefined in CSS 2.
                        // However, it is suggested that, if the containing block's width
                        // does not itself depend on the replaced element's width,
                        // then the used value of 'width' is calculated from the constraint
                        // equation used for block-level, non-replaced elements in normal flow.”
                        _ => default_object_size().inline,
                    };
                let block_size = if let Some(block) = intrinsic_size.block {
                    block
                } else if let Some(i_over_b) = intrinsic_ratio {
                    // “used width” in CSS 2 is what we just computed above
                    inline_size / i_over_b
                } else {
                    default_object_size().block
                };

                let i_over_b = if let Some(i_over_b) = intrinsic_ratio {
                    i_over_b
                } else {
                    return clamp(inline_size, block_size);
                };

                // https://drafts.csswg.org/css2/visudet.html#min-max-widths
                // “However, for replaced elements with an intrinsic ratio and both
                //  'width' and 'height' specified as 'auto', the algorithm is as follows”
                enum Violation {
                    None,
                    Below(Length),
                    Above(Length),
                }
                let violation = |size, min_size, mut max_size: Option<Length>| {
                    if let Some(max) = max_size.as_mut() {
                        max.max_assign(min_size);
                    }
                    if size < min_size {
                        return Violation::Below(min_size);
                    }
                    match max_size {
                        Some(max_size) if size > max_size => Violation::Above(max_size),
                        _ => Violation::None,
                    }
                };
                match (
                    violation(inline_size, min_box_size.inline, max_box_size.inline),
                    violation(block_size, min_box_size.block, max_box_size.block),
                ) {
                    // Row 1.
                    (Violation::None, Violation::None) => Vec2 {
                        inline: inline_size,
                        block: block_size,
                    },
                    // Row 2.
                    (Violation::Above(max_inline_size), Violation::None) => Vec2 {
                        inline: max_inline_size,
                        block: (max_inline_size / i_over_b).max(min_box_size.block),
                    },
                    // Row 3.
                    (Violation::Below(min_inline_size), Violation::None) => Vec2 {
                        inline: min_inline_size,
                        block: (min_inline_size / i_over_b).clamp_below_max(max_box_size.block),
                    },
                    // Row 4.
                    (Violation::None, Violation::Above(max_block_size)) => Vec2 {
                        inline: (max_block_size * i_over_b).max(min_box_size.inline),
                        block: max_block_size,
                    },
                    // Row 5.
                    (Violation::None, Violation::Below(min_block_size)) => Vec2 {
                        inline: (min_block_size * i_over_b).clamp_below_max(max_box_size.inline),
                        block: min_block_size,
                    },
                    // Rows 6-7.
                    (Violation::Above(max_inline_size), Violation::Above(max_block_size)) => {
                        if max_inline_size.px() / inline_size.px() <=
                            max_block_size.px() / block_size.px()
                        {
                            // Row 6.
                            Vec2 {
                                inline: max_inline_size,
                                block: (max_inline_size / i_over_b).max(min_box_size.block),
                            }
                        } else {
                            // Row 7.
                            Vec2 {
                                inline: (max_block_size * i_over_b).max(min_box_size.inline),
                                block: max_block_size,
                            }
                        }
                    },
                    // Rows 8-9.
                    (Violation::Below(min_inline_size), Violation::Below(min_block_size)) => {
                        if min_inline_size.px() / inline_size.px() <=
                            min_block_size.px() / block_size.px()
                        {
                            // Row 8.
                            Vec2 {
                                inline: (min_block_size * i_over_b)
                                    .clamp_below_max(max_box_size.inline),
                                block: min_block_size,
                            }
                        } else {
                            // Row 9.
                            Vec2 {
                                inline: min_inline_size,
                                block: (min_inline_size / i_over_b)
                                    .clamp_below_max(max_box_size.block),
                            }
                        }
                    },
                    // Row 10.
                    (Violation::Below(min_inline_size), Violation::Above(max_block_size)) => Vec2 {
                        inline: min_inline_size,
                        block: max_block_size,
                    },
                    // Row 11.
                    (Violation::Above(max_inline_size), Violation::Below(min_block_size)) => Vec2 {
                        inline: max_inline_size,
                        block: min_block_size,
                    },
                }
            },
        }
    }
}