egui 0.33.2

An easy-to-use immediate mode GUI that runs on both web and native
Documentation 
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use std::sync::Arc;

use crate::{Galley, Painter, Rect, Ui, Visuals, pos2, vec2};

use super::CCursorRange;

#[derive(Clone, Debug)]
pub struct RowVertexIndices {
    pub row: usize,
    pub vertex_indices: [u32; 6],
}

/// Adds text selection rectangles to the galley.
pub fn paint_text_selection(
    galley: &mut Arc<Galley>,
    visuals: &Visuals,
    cursor_range: &CCursorRange,
    mut new_vertex_indices: Option<&mut Vec<RowVertexIndices>>,
) {
    if cursor_range.is_empty() {
        return;
    }

    // We need to modify the galley (add text selection painting to it),
    // and so we need to clone it if it is shared:
    let galley: &mut Galley = Arc::make_mut(galley);

    let color = visuals.selection.bg_fill;
    let [min, max] = cursor_range.sorted_cursors();
    let min = galley.layout_from_cursor(min);
    let max = galley.layout_from_cursor(max);

    for ri in min.row..=max.row {
        let row = Arc::make_mut(&mut galley.rows[ri].row);

        let left = if ri == min.row {
            row.x_offset(min.column)
        } else {
            0.0
        };
        let right = if ri == max.row {
            row.x_offset(max.column)
        } else {
            let newline_size = if row.ends_with_newline {
                row.height() / 2.0 // visualize that we select the newline
            } else {
                0.0
            };
            row.size.x + newline_size
        };

        let rect = Rect::from_min_max(pos2(left, 0.0), pos2(right, row.size.y));
        let mesh = &mut row.visuals.mesh;

        // Time to insert the selection rectangle into the row mesh.
        // It should be on top (after) of any background in the galley,
        // but behind (before) any glyphs. The row visuals has this information:
        let glyph_index_start = row.visuals.glyph_index_start;

        // Start by appending the selection rectangle to end of the mesh, as two triangles (= 6 indices):
        let num_indices_before = mesh.indices.len();
        mesh.add_colored_rect(rect, color);
        assert_eq!(
            num_indices_before + 6,
            mesh.indices.len(),
            "We expect exactly 6 new indices"
        );

        // Copy out the new triangles:
        let selection_triangles = [
            mesh.indices[num_indices_before],
            mesh.indices[num_indices_before + 1],
            mesh.indices[num_indices_before + 2],
            mesh.indices[num_indices_before + 3],
            mesh.indices[num_indices_before + 4],
            mesh.indices[num_indices_before + 5],
        ];

        // Move every old triangle forwards by 6 indices to make room for the new triangle:
        for i in (glyph_index_start..num_indices_before).rev() {
            mesh.indices.swap(i, i + 6);
        }
        // Put the new triangle in place:
        mesh.indices[glyph_index_start..glyph_index_start + 6]
            .clone_from_slice(&selection_triangles);

        row.visuals.mesh_bounds = mesh.calc_bounds();

        if let Some(new_vertex_indices) = &mut new_vertex_indices {
            new_vertex_indices.push(RowVertexIndices {
                row: ri,
                vertex_indices: selection_triangles,
            });
        }
    }
}

/// Paint one end of the selection, e.g. the primary cursor.
///
/// This will never blink.
pub fn paint_cursor_end(painter: &Painter, visuals: &Visuals, cursor_rect: Rect) {
    let stroke = visuals.text_cursor.stroke;

    let top = cursor_rect.center_top();
    let bottom = cursor_rect.center_bottom();

    painter.line_segment([top, bottom], (stroke.width, stroke.color));

    if false {
        // Roof/floor:
        let extrusion = 3.0;
        let width = 1.0;
        painter.line_segment(
            [top - vec2(extrusion, 0.0), top + vec2(extrusion, 0.0)],
            (width, stroke.color),
        );
        painter.line_segment(
            [bottom - vec2(extrusion, 0.0), bottom + vec2(extrusion, 0.0)],
            (width, stroke.color),
        );
    }
}

/// Paint one end of the selection, e.g. the primary cursor, with blinking (if enabled).
pub fn paint_text_cursor(
    ui: &Ui,
    painter: &Painter,
    primary_cursor_rect: Rect,
    time_since_last_interaction: f64,
) {
    if ui.visuals().text_cursor.blink {
        let on_duration = ui.visuals().text_cursor.on_duration;
        let off_duration = ui.visuals().text_cursor.off_duration;
        let total_duration = on_duration + off_duration;

        let time_in_cycle = (time_since_last_interaction % (total_duration as f64)) as f32;

        let wake_in = if time_in_cycle < on_duration {
            // Cursor is visible
            paint_cursor_end(painter, ui.visuals(), primary_cursor_rect);
            on_duration - time_in_cycle
        } else {
            // Cursor is not visible
            total_duration - time_in_cycle
        };

        ui.ctx().request_repaint_after_secs(wake_in);
    } else {
        paint_cursor_end(painter, ui.visuals(), primary_cursor_rect);
    }
}