egui/egui_extras/src/layout.rs

use egui::{Pos2, Rect, Response, Sense, Ui};

#[derive(Clone, Copy)]
pub(crate) enum CellSize {
    /// Absolute size in points
    Absolute(f32),
    /// Take all available space
    Remainder,
}

/// Cells are positioned in two dimensions, cells go in one direction and form lines.
///
/// In a strip there's only one line which goes in the direction of the strip:
///
/// In a horizontal strip, a `[StripLayout]` with horizontal `[CellDirection]` is used.
/// Its cells go from left to right inside this `[StripLayout]`.
///
/// In a table there's a `[StripLayout]` for each table row with a horizontal `[CellDirection]`.
/// Its cells go from left to right. And the lines go from top to bottom.
pub(crate) enum CellDirection {
    /// Cells go from left to right.
    Horizontal,
    /// Cells go from top to bottom.
    Vertical,
}

/// Positions cells in `[CellDirection]` and starts a new line on `[StripLayout::end_line]`
pub struct StripLayout<'l> {
    ui: &'l mut Ui,
    direction: CellDirection,
    rect: Rect,
    cursor: Pos2,
    max: Pos2,
    pub(crate) clip: bool,
}

impl<'l> StripLayout<'l> {
    pub(crate) fn new(ui: &'l mut Ui, direction: CellDirection, clip: bool) -> Self {
        let rect = ui.available_rect_before_wrap();
        let pos = rect.left_top();

        Self {
            ui,
            rect,
            cursor: pos,
            max: pos,
            direction,
            clip,
        }
    }

    pub fn current_y(&self) -> f32 {
        self.rect.top()
    }

    fn cell_rect(&self, width: &CellSize, height: &CellSize) -> Rect {
        Rect {
            min: self.cursor,
            max: Pos2 {
                x: match width {
                    CellSize::Absolute(width) => self.cursor.x + width,
                    CellSize::Remainder => self.rect.right(),
                },
                y: match height {
                    CellSize::Absolute(height) => self.cursor.y + height,
                    CellSize::Remainder => self.rect.bottom(),
                },
            },
        }
    }

    fn set_pos(&mut self, rect: Rect) {
        self.max.x = self.max.x.max(rect.right());
        self.max.y = self.max.y.max(rect.bottom());

        match self.direction {
            CellDirection::Horizontal => {
                self.cursor.x = rect.right() + self.ui.spacing().item_spacing.x;
            }
            CellDirection::Vertical => {
                self.cursor.y = rect.bottom() + self.ui.spacing().item_spacing.y;
            }
        }
    }

    pub(crate) fn empty(&mut self, width: CellSize, height: CellSize) {
        self.set_pos(self.cell_rect(&width, &height));
    }

    pub(crate) fn add(
        &mut self,
        width: CellSize,
        height: CellSize,
        add_contents: impl FnOnce(&mut Ui),
    ) -> Response {
        let rect = self.cell_rect(&width, &height);
        let used_rect = self.cell(rect, add_contents);
        self.set_pos(rect);
        self.ui.allocate_rect(rect.union(used_rect), Sense::hover())
    }

    pub(crate) fn add_striped(
        &mut self,
        width: CellSize,
        height: CellSize,
        add_contents: impl FnOnce(&mut Ui),
    ) -> Response {
        let rect = self.cell_rect(&width, &height);

        // Make sure we don't have a gap in the stripe background:
        let rect = rect.expand2(egui::vec2(0.5 * self.ui.spacing().item_spacing.x, 0.0));

        self.ui
            .painter()
            .rect_filled(rect, 0.0, self.ui.visuals().faint_bg_color);

        self.add(width, height, add_contents)
    }

    /// only needed for layouts with multiple lines, like [`Table`](crate::Table).
    pub fn end_line(&mut self) {
        match self.direction {
            CellDirection::Horizontal => {
                self.cursor.y = self.max.y + self.ui.spacing().item_spacing.y;
                self.cursor.x = self.rect.left();
            }
            CellDirection::Vertical => {
                self.cursor.x = self.max.x + self.ui.spacing().item_spacing.x;
                self.cursor.y = self.rect.top();
            }
        }
    }

    fn cell(&mut self, rect: Rect, add_contents: impl FnOnce(&mut Ui)) -> Rect {
        let mut child_ui = self.ui.child_ui(rect, *self.ui.layout());

        if self.clip {
            child_ui.set_clip_rect(child_ui.clip_rect().intersect(rect));
        }

        add_contents(&mut child_ui);
        child_ui.min_rect()
    }

    /// Allocate the rect in [`Self::ui`] so that the scrollview knows about our size
    pub fn allocate_rect(&mut self) -> Response {
        let mut rect = self.rect;
        rect.set_right(self.max.x);
        rect.set_bottom(self.max.y);

        self.ui.allocate_rect(rect, Sense::hover())
    }
}