servo/components/layout/multicol.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/. */

//! CSS Multi-column layout <http://dev.w3.org/csswg/css-multicol/>

use std::cmp::{max, min};
use std::fmt;
use std::sync::Arc;

use app_units::Au;
use base::print_tree::PrintTree;
use euclid::default::{Point2D, Vector2D};
use log::{debug, trace};
use style::logical_geometry::LogicalSize;
use style::properties::ComputedValues;
use style::values::computed::length::{
    NonNegativeLengthOrAuto, NonNegativeLengthPercentageOrNormal,
};
use style::values::generics::column::ColumnCount;

use crate::ServoArc;
use crate::block::BlockFlow;
use crate::context::LayoutContext;
use crate::display_list::{DisplayListBuildState, StackingContextCollectionState};
use crate::floats::FloatKind;
use crate::flow::{Flow, FlowClass, FragmentationContext, GetBaseFlow, OpaqueFlow};
use crate::fragment::{Fragment, FragmentBorderBoxIterator, Overflow};

#[allow(unsafe_code)]
unsafe impl crate::flow::HasBaseFlow for MulticolFlow {}

#[repr(C)]
pub struct MulticolFlow {
    pub block_flow: BlockFlow,

    /// Length between the inline-start edge of a column and that of the next.
    /// That is, the used column-width + used column-gap.
    pub column_pitch: Au,
}

#[allow(unsafe_code)]
unsafe impl crate::flow::HasBaseFlow for MulticolColumnFlow {}

#[repr(C)]
pub struct MulticolColumnFlow {
    pub block_flow: BlockFlow,
}

impl MulticolFlow {
    pub fn from_fragment(fragment: Fragment, float_kind: Option<FloatKind>) -> MulticolFlow {
        MulticolFlow {
            block_flow: BlockFlow::from_fragment_and_float_kind(fragment, float_kind),
            column_pitch: Au(0),
        }
    }
}

impl MulticolColumnFlow {
    pub fn from_fragment(fragment: Fragment) -> MulticolColumnFlow {
        MulticolColumnFlow {
            block_flow: BlockFlow::from_fragment(fragment),
        }
    }
}

impl Flow for MulticolFlow {
    fn class(&self) -> FlowClass {
        FlowClass::Multicol
    }

    fn as_mut_block(&mut self) -> &mut BlockFlow {
        &mut self.block_flow
    }

    fn as_block(&self) -> &BlockFlow {
        &self.block_flow
    }

    fn bubble_inline_sizes(&mut self) {
        // FIXME(SimonSapin) http://dev.w3.org/csswg/css-sizing/#multicol-intrinsic
        self.block_flow.bubble_inline_sizes();
    }

    fn assign_inline_sizes(&mut self, layout_context: &LayoutContext) {
        debug!(
            "assign_inline_sizes({}): assigning inline_size for flow",
            "multicol"
        );
        trace!("MulticolFlow before assigning: {:?}", &self);

        let shared_context = layout_context.shared_context();
        self.block_flow.compute_inline_sizes(shared_context);

        // Move in from the inline-start border edge.
        let inline_start_content_edge = self.block_flow.fragment.border_box.start.i +
            self.block_flow.fragment.border_padding.inline_start;

        // Distance from the inline-end margin edge to the inline-end content edge.
        let inline_end_content_edge = self.block_flow.fragment.margin.inline_end +
            self.block_flow.fragment.border_padding.inline_end;

        self.block_flow.assign_inline_sizes(layout_context);
        let padding_and_borders = self.block_flow.fragment.border_padding.inline_start_end();
        let content_inline_size =
            self.block_flow.fragment.border_box.size.inline - padding_and_borders;
        let column_width;
        {
            let style = &self.block_flow.fragment.style;
            let column_gap = Au::from(match style.get_position().column_gap {
                NonNegativeLengthPercentageOrNormal::LengthPercentage(ref len) => {
                    len.0.to_pixel_length(content_inline_size)
                },
                NonNegativeLengthPercentageOrNormal::Normal => self
                    .block_flow
                    .fragment
                    .style
                    .get_font()
                    .font_size
                    .computed_size(),
            });

            let column_style = style.get_column();
            let mut column_count;
            if let NonNegativeLengthOrAuto::LengthPercentage(column_width) =
                column_style.column_width
            {
                let column_width = Au::from(column_width);
                column_count = max(
                    1,
                    (content_inline_size + column_gap).0 / (column_width + column_gap).0,
                );
                if let ColumnCount::Integer(specified_column_count) = column_style.column_count {
                    column_count = min(column_count, specified_column_count.0);
                }
            } else {
                column_count = match column_style.column_count {
                    ColumnCount::Integer(n) => n.0,
                    _ => unreachable!(),
                }
            }
            column_width = max(
                Au(0),
                (content_inline_size + column_gap) / column_count - column_gap,
            );
            self.column_pitch = column_width + column_gap;
        }

        self.block_flow.fragment.border_box.size.inline = content_inline_size + padding_and_borders;

        self.block_flow.propagate_assigned_inline_size_to_children(
            shared_context,
            inline_start_content_edge,
            inline_end_content_edge,
            column_width,
            |_, _, _, _, _, _| {},
        );

        trace!("MulticolFlow after assigning: {:?}", &self);
    }

    fn assign_block_size(&mut self, ctx: &LayoutContext) {
        debug!("assign_block_size: assigning block_size for multicol");
        trace!("MulticolFlow before assigning: {:?}", &self);

        let fragmentation_context = Some(FragmentationContext {
            this_fragment_is_empty: true,
            available_block_size: {
                let style = &self.block_flow.fragment.style;
                let size = style
                    .content_block_size()
                    .maybe_to_used_value(None)
                    .or_else(|| style.max_block_size().maybe_to_used_value(None));

                size.unwrap_or_else(|| {
                    // FIXME: do column balancing instead
                    // FIXME: (until column balancing) substract margins/borders/padding
                    LogicalSize::from_physical(
                        self.block_flow.base.writing_mode,
                        ctx.shared_context().viewport_size(),
                    )
                    .block
                })
            },
        });

        // Before layout, everything is in a single "column"
        assert_eq!(self.block_flow.base.children.len(), 1);
        let mut column = self.block_flow.base.children.pop_front_arc().unwrap();

        // Pretend there is no children for this:
        self.block_flow.assign_block_size(ctx);

        loop {
            let remaining = Arc::get_mut(&mut column)
                .unwrap()
                .fragment(ctx, fragmentation_context);
            self.block_flow.base.children.push_back_arc(column);
            column = match remaining {
                Some(remaining) => remaining,
                None => break,
            };
        }

        trace!("MulticolFlow after assigning: {:?}", &self);
    }

    fn compute_stacking_relative_position(&mut self, layout_context: &LayoutContext) {
        self.block_flow
            .compute_stacking_relative_position(layout_context);
        let pitch = LogicalSize::new(self.block_flow.base.writing_mode, self.column_pitch, Au(0));
        let pitch = pitch.to_physical(self.block_flow.base.writing_mode);
        for (i, child) in self.block_flow.base.children.iter_mut().enumerate() {
            let point = &mut child.mut_base().stacking_relative_position;
            *point += Vector2D::new(pitch.width * i as i32, pitch.height * i as i32);
        }
    }

    fn update_late_computed_inline_position_if_necessary(&mut self, inline_position: Au) {
        self.block_flow
            .update_late_computed_inline_position_if_necessary(inline_position)
    }

    fn update_late_computed_block_position_if_necessary(&mut self, block_position: Au) {
        self.block_flow
            .update_late_computed_block_position_if_necessary(block_position)
    }

    fn build_display_list(&mut self, state: &mut DisplayListBuildState) {
        debug!("build_display_list_multicol");
        self.block_flow.build_display_list(state);
    }

    fn collect_stacking_contexts(&mut self, state: &mut StackingContextCollectionState) {
        self.block_flow.collect_stacking_contexts(state);
    }

    fn repair_style(&mut self, new_style: &ServoArc<ComputedValues>) {
        self.block_flow.repair_style(new_style)
    }

    fn compute_overflow(&self) -> Overflow {
        self.block_flow.compute_overflow()
    }

    fn contains_roots_of_absolute_flow_tree(&self) -> bool {
        self.block_flow.contains_roots_of_absolute_flow_tree()
    }

    fn is_absolute_containing_block(&self) -> bool {
        self.block_flow.is_absolute_containing_block()
    }

    fn generated_containing_block_size(&self, flow: OpaqueFlow) -> LogicalSize<Au> {
        self.block_flow.generated_containing_block_size(flow)
    }

    fn iterate_through_fragment_border_boxes(
        &self,
        iterator: &mut dyn FragmentBorderBoxIterator,
        level: i32,
        stacking_context_position: &Point2D<Au>,
    ) {
        self.block_flow.iterate_through_fragment_border_boxes(
            iterator,
            level,
            stacking_context_position,
        );
    }

    fn mutate_fragments(&mut self, mutator: &mut dyn FnMut(&mut Fragment)) {
        self.block_flow.mutate_fragments(mutator);
    }

    fn print_extra_flow_children(&self, print_tree: &mut PrintTree) {
        self.block_flow.print_extra_flow_children(print_tree);
    }
}

impl Flow for MulticolColumnFlow {
    fn class(&self) -> FlowClass {
        FlowClass::MulticolColumn
    }

    fn as_mut_block(&mut self) -> &mut BlockFlow {
        &mut self.block_flow
    }

    fn as_block(&self) -> &BlockFlow {
        &self.block_flow
    }

    fn bubble_inline_sizes(&mut self) {
        self.block_flow.bubble_inline_sizes();
    }

    fn assign_inline_sizes(&mut self, layout_context: &LayoutContext) {
        debug!(
            "assign_inline_sizes({}): assigning inline_size for flow",
            "multicol column"
        );
        trace!("MulticolFlow before assigning: {:?}", &self);

        self.block_flow.assign_inline_sizes(layout_context);
        trace!("MulticolFlow after assigning: {:?}", &self);
    }

    fn assign_block_size(&mut self, ctx: &LayoutContext) {
        debug!("assign_block_size: assigning block_size for multicol column");
        trace!("MulticolFlow before assigning: {:?}", &self);

        self.block_flow.assign_block_size(ctx);

        trace!("MulticolFlow after assigning: {:?}", &self);
    }

    fn fragment(
        &mut self,
        layout_context: &LayoutContext,
        fragmentation_context: Option<FragmentationContext>,
    ) -> Option<Arc<dyn Flow>> {
        Flow::fragment(&mut self.block_flow, layout_context, fragmentation_context)
    }

    fn compute_stacking_relative_position(&mut self, layout_context: &LayoutContext) {
        self.block_flow
            .compute_stacking_relative_position(layout_context)
    }

    fn update_late_computed_inline_position_if_necessary(&mut self, inline_position: Au) {
        self.block_flow
            .update_late_computed_inline_position_if_necessary(inline_position)
    }

    fn update_late_computed_block_position_if_necessary(&mut self, block_position: Au) {
        self.block_flow
            .update_late_computed_block_position_if_necessary(block_position)
    }

    fn build_display_list(&mut self, state: &mut DisplayListBuildState) {
        debug!("build_display_list_multicol column");
        self.block_flow.build_display_list(state);
    }

    fn collect_stacking_contexts(&mut self, state: &mut StackingContextCollectionState) {
        self.block_flow.collect_stacking_contexts(state);
    }

    fn repair_style(&mut self, new_style: &ServoArc<ComputedValues>) {
        self.block_flow.repair_style(new_style)
    }

    fn compute_overflow(&self) -> Overflow {
        self.block_flow.compute_overflow()
    }

    fn contains_roots_of_absolute_flow_tree(&self) -> bool {
        self.block_flow.contains_roots_of_absolute_flow_tree()
    }

    fn is_absolute_containing_block(&self) -> bool {
        self.block_flow.is_absolute_containing_block()
    }

    fn generated_containing_block_size(&self, flow: OpaqueFlow) -> LogicalSize<Au> {
        self.block_flow.generated_containing_block_size(flow)
    }

    fn iterate_through_fragment_border_boxes(
        &self,
        iterator: &mut dyn FragmentBorderBoxIterator,
        level: i32,
        stacking_context_position: &Point2D<Au>,
    ) {
        self.block_flow.iterate_through_fragment_border_boxes(
            iterator,
            level,
            stacking_context_position,
        );
    }

    fn mutate_fragments(&mut self, mutator: &mut dyn FnMut(&mut Fragment)) {
        self.block_flow.mutate_fragments(mutator);
    }

    fn print_extra_flow_children(&self, print_tree: &mut PrintTree) {
        self.block_flow.print_extra_flow_children(print_tree);
    }
}

impl fmt::Debug for MulticolFlow {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "MulticolFlow: {:?}", self.block_flow)
    }
}

impl fmt::Debug for MulticolColumnFlow {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "MulticolColumnFlow: {:?}", self.block_flow)
    }
}