kas_core/theme/

draw.rs

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License in the LICENSE-APACHE file or at:
//     https://www.apache.org/licenses/LICENSE-2.0

//! Widget-facing high-level draw API

use winit::keyboard::Key;

use super::{FrameStyle, MarkStyle, SelectionStyle, SizeCx, Text, ThemeSize};
use crate::dir::Direction;
use crate::draw::color::{ParseError, Rgb, Rgba};
use crate::draw::{Draw, DrawIface, DrawRounded, DrawShared, DrawSharedImpl, ImageId, PassType};
use crate::event::EventState;
#[allow(unused)] use crate::event::{Command, ConfigCx};
use crate::geom::{Coord, Offset, Rect};
use crate::text::{Effect, TextDisplay, format::FormattableText};
use crate::theme::ColorsLinear;
use crate::{Id, Tile, autoimpl};
#[allow(unused)] use crate::{Layout, theme::TextClass};
use std::ops::Range;
use std::time::Instant;

/// Optional background colour
#[derive(Copy, Clone, Debug, Default, PartialEq)]
pub enum Background {
    /// Use theme/feature's default
    #[default]
    Default,
    /// Error state
    Error,
    /// A given color
    Rgb(Rgb),
}

impl From<Rgb> for Background {
    #[inline]
    fn from(color: Rgb) -> Self {
        Background::Rgb(color)
    }
}

#[derive(Copy, Clone, Debug, thiserror::Error)]
pub enum BackgroundParseError {
    /// No `#` prefix
    ///
    /// NOTE: this exists to allow the possibility of supporting new exprs like
    /// "Default" or "Error".
    #[error("Unknown: no `#` prefix")]
    Unknown,
    /// Invalid hex
    #[error("invalid hex sequence")]
    InvalidRgb(#[from] ParseError),
}

impl std::str::FromStr for Background {
    type Err = BackgroundParseError;

    #[inline]
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s.starts_with("#") {
            Rgb::from_str(s).map(|c| c.into()).map_err(|e| e.into())
        } else {
            Err(BackgroundParseError::Unknown)
        }
    }
}

/// Draw interface
///
/// This interface is provided to widgets in [`Layout::draw`].
/// Lower-level interfaces may be accessed through [`Self::draw`].
///
/// `DrawCx` is not a `Copy` or `Clone` type; instead it may be "reborrowed"
/// via [`Self::re`].
///
/// -   `draw.check_box(&*self, self.state);` — note `&*self` to convert from to
///     `&W` from `&mut W`, since the latter would cause borrow conflicts
#[autoimpl(Debug ignore self.h)]
pub struct DrawCx<'a> {
    h: &'a mut dyn ThemeDraw,
    id: Id,
}

impl<'a> DrawCx<'a> {
    /// Reborrow with a new lifetime
    ///
    /// Rust allows references like `&T` or `&mut T` to be "reborrowed" through
    /// coercion: essentially, the pointer is copied under a new, shorter, lifetime.
    /// Until rfcs#1403 lands, reborrows on user types require a method call.
    #[inline(always)]
    pub fn re<'b>(&'b mut self) -> DrawCx<'b>
    where
        'a: 'b,
    {
        DrawCx {
            h: self.h,
            id: self.id.clone(),
        }
    }

    /// Construct from a [`DrawCx`] and [`EventState`]
    #[cfg_attr(not(feature = "internal_doc"), doc(hidden))]
    #[cfg_attr(docsrs, doc(cfg(internal_doc)))]
    pub(crate) fn new(h: &'a mut dyn ThemeDraw, id: Id) -> Self {
        DrawCx { h, id }
    }

    /// Set the identity of the current widget
    ///
    /// This struct tracks the [`Id`] of the calling widget to allow evaluation
    /// of widget state (e.g. is disabled, is under the mouse, has key focus).
    /// Usually you don't need to worry about this since the `#[widget]` macro
    /// injects a call to this method at the start of [`Layout::draw`].
    pub fn set_id(&mut self, id: Id) {
        self.id = id;
    }

    /// Access event-management state
    pub fn ev_state(&mut self) -> &mut EventState {
        self.h.components().2
    }

    /// Access a [`SizeCx`]
    ///
    /// (This also allows access to [`EventState`].)
    pub fn size_cx(&mut self) -> SizeCx<'_> {
        let (w, _, es) = self.h.components();
        SizeCx::new(es, w)
    }

    /// Access theme colors
    pub fn colors(&self) -> &ColorsLinear {
        self.h.colors()
    }

    /// Access a [`DrawShared`]
    pub fn draw_shared(&mut self) -> &mut dyn DrawShared {
        self.h.components().1.shared()
    }

    /// Access the low-level draw device
    ///
    /// Note: this drawing API is modular, with limited functionality in the
    /// base trait [`Draw`]. To access further functionality, it is necessary
    /// to downcast with [`crate::draw::DrawIface::downcast_from`].
    pub fn draw(&mut self) -> &mut dyn Draw {
        self.h.components().1
    }

    /// Access the draw device as a [`DrawRounded`] implementation, if possible
    ///
    /// Warning: this does not reflect whether the underlying draw device
    /// supports [`DrawRounded`] (which would require specialization) but
    /// whether the theme in question requires [`DrawRounded`]. As such, this
    /// method is only useful with a theme requiring this extension such as
    /// [`FlatTheme`](super::FlatTheme).
    pub fn draw_rounded(&mut self) -> Option<&mut dyn DrawRounded> {
        self.h.draw_rounded()
    }

    /// Access the low-level draw device (implementation type)
    ///
    /// The implementing type must be specified. See [`DrawIface::downcast_from`].
    pub fn draw_iface<DS: DrawSharedImpl>(&mut self) -> Option<DrawIface<'_, DS>> {
        DrawIface::downcast_from(self.draw())
    }

    /// Draw to a new pass
    ///
    /// Adds a new draw pass for purposes of enforcing draw order. Content of
    /// the new pass will be drawn after content in the parent pass.
    ///
    /// Warning: the number of passes used can have a substantial performance
    /// impact, potentially more on GPU communication than CPU usage.
    pub fn with_pass<F: FnOnce(DrawCx)>(&mut self, f: F) {
        let clip_rect = self.h.get_clip_rect();
        let id = self.id.clone();
        self.h.new_pass(
            clip_rect,
            Offset::ZERO,
            PassType::Clip,
            Box::new(|h| f(DrawCx { h, id })),
        );
    }

    /// Draw to a new pass with clipping and offset (e.g. for scrolling)
    ///
    /// Adds a new draw pass of type [`PassType::Clip`], with draw operations
    /// clipped to `rect` and translated by `offset.
    ///
    /// Warning: the number of passes used can have a substantial performance
    /// impact, potentially more on GPU communication than CPU usage.
    pub fn with_clip_region<F: FnOnce(DrawCx)>(&mut self, rect: Rect, offset: Offset, f: F) {
        let id = self.id.clone();
        self.h.new_pass(
            rect,
            offset,
            PassType::Clip,
            Box::new(|h| f(DrawCx { h, id })),
        );
    }

    /// Draw to a new pass as an overlay (e.g. for pop-up menus)
    ///
    /// Adds a new draw pass of type [`PassType::Overlay`], with draw operations
    /// clipped to `rect`.
    ///
    /// The theme is permitted to enlarge the `rect` for the purpose of drawing
    /// a frame or shadow around this overlay, thus the
    /// [`Self::get_clip_rect`] may be larger than expected.
    ///
    /// Warning: the number of passes used can have a substantial performance
    /// impact, potentially more on GPU communication than CPU usage.
    pub fn with_overlay<F: FnOnce(DrawCx)>(&mut self, rect: Rect, offset: Offset, f: F) {
        let id = self.id.clone();
        self.h.new_pass(
            rect,
            offset,
            PassType::Overlay,
            Box::new(|h| f(DrawCx { h, id })),
        );
    }

    /// Target area for drawing
    ///
    /// Drawing is restricted to this [`Rect`], which may be the whole window, a
    /// [clip region](Self::with_clip_region) or an
    /// [overlay](Self::with_overlay). This may be used to cull hidden
    /// items from lists inside a scrollable view.
    pub fn get_clip_rect(&mut self) -> Rect {
        self.h.get_clip_rect()
    }

    /// Register widget `id` as handler of an access `key`
    ///
    /// An *access key* (also known as mnemonic) is a shortcut key able to
    /// directly open menus, activate buttons, etc. Usually this requires that
    /// the <kbd>Alt</kbd> is held, though
    /// [alt-bypass mode](crate::window::Window::with_alt_bypass) is available.
    ///
    /// The widget `id` is bound to the given `key`, if available. When the
    /// access key is pressed (assuming that this binding succeeds), widget `id`
    /// will receive navigation focus (if supported; otherwise an ancestor may
    /// receive focus) and is sent [`Command::Activate`] (likewise, an ancestor
    /// may handle this if widget `id` does not).
    ///
    /// If multiple widgets attempt to register themselves as handlers of the
    /// same `key`, then only the first succeeds.
    ///
    /// Returns `true` when the key should be underlined.
    pub fn access_key(&mut self, id: &Id, key: &Key) -> bool {
        self.ev_state().add_access_key_binding(id, key)
    }

    /// Draw a frame inside the given `rect`
    ///
    /// The frame dimensions are given by [`SizeCx::frame`].
    pub fn frame(&mut self, rect: Rect, style: FrameStyle, bg: Background) {
        self.h.frame(&self.id, rect, style, bg)
    }

    /// Draw a separator in the given `rect`
    pub fn separator(&mut self, rect: Rect) {
        self.h.separator(rect);
    }

    /// Draw a selection highlight / frame
    ///
    /// Adjusts the background color and/or draws a line around the given rect.
    /// In the latter case, a margin of size [`SizeCx::inner_margins`] around
    /// `rect` is expected.
    pub fn selection(&mut self, rect: Rect, style: SelectionStyle) {
        self.h.selection(rect, style);
    }

    /// Draw text
    ///
    /// Text is clipped to `rect`.
    ///
    /// This is a convenience method over [`Self::text_with_effects`].
    ///
    /// The `text` should be prepared before calling this method.
    pub fn text<T: FormattableText>(&mut self, rect: Rect, text: &Text<T>) {
        self.text_with_position(rect.pos, rect, text);
    }

    /// Draw text with specified color
    ///
    /// Text is clipped to `rect` and drawn using `color`.
    ///
    /// This is a convenience method over [`Self::text_with_effects`].
    ///
    /// The `text` should be prepared before calling this method.
    pub fn text_with_color<T: FormattableText>(&mut self, rect: Rect, text: &Text<T>, color: Rgba) {
        let effects = text.effect_tokens();
        self.text_with_effects(rect.pos, rect, text, &[color], effects);
    }

    /// Draw text with effects and an offset
    ///
    /// Text is clipped to `rect`, drawing from `pos`; use `pos = rect.pos` if
    /// the text is not scrolled.
    ///
    /// This is a convenience method over [`Self::text_with_effects`].
    ///
    /// The `text` should be prepared before calling this method.
    pub fn text_with_position<T: FormattableText>(
        &mut self,
        pos: Coord,
        rect: Rect,
        text: &Text<T>,
    ) {
        let effects = text.effect_tokens();
        self.text_with_effects(pos, rect, text, &[], effects);
    }

    /// Draw text with a given effect list
    ///
    /// Text is clipped to `rect`, drawing from `pos`; use `pos = rect.pos` if
    /// the text is not scrolled.
    ///
    /// If `colors` is empty, it is replaced with a single theme-defined color.
    /// Text is then drawn using `colors[0]` except as specified by effects.
    ///
    /// The list of `effects` (if not empty) controls render effects:
    /// [`Effect::e`] is an index into `colors` while [`Effect::flags`] controls
    /// underline and strikethrough. [`Effect::start`] is the text index at
    /// which this effect first takes effect, and must effects must be ordered
    /// such that the sequence of [`Effect::start`] values is strictly
    /// increasing. [`Effect::default()`] is used if `effects` is empty or while
    /// `index < effects.first().unwrap().start`.
    ///
    /// Text objects may embed their own list of effects, accessible using
    /// [`Text::effect_tokens`]. It is always valid to disregard these
    /// and use a custom `effects` list or empty list.
    pub fn text_with_effects<T: FormattableText>(
        &mut self,
        pos: Coord,
        rect: Rect,
        text: &Text<T>,
        colors: &[Rgba],
        effects: &[Effect],
    ) {
        if let Ok(display) = text.display() {
            if effects.is_empty() {
                // Use the faster and simpler implementation when we don't have effects
                self.h
                    .text(&self.id, pos, rect, display, colors.first().cloned());
            } else {
                if cfg!(debug_assertions) {
                    let num_colors = if colors.is_empty() { 1 } else { colors.len() };
                    let mut i = 0;
                    for effect in effects {
                        assert!(effect.start >= i);
                        i = effect.start;

                        assert!(usize::from(effect.e) < num_colors);
                    }
                }

                self.h
                    .text_effects(&self.id, pos, rect, display, colors, effects);
            }
        }
    }

    /// Draw some text with a selection
    ///
    /// Text is drawn like [`Self::text_with_position`] except that the subset
    /// identified by `range` is highlighted using theme-defined colors.
    pub fn text_with_selection<T: FormattableText>(
        &mut self,
        pos: Coord,
        rect: Rect,
        text: &Text<T>,
        range: Range<usize>,
    ) {
        if range.is_empty() {
            return self.text_with_position(pos, rect, text);
        }

        let Ok(display) = text.display() else {
            return;
        };

        self.h
            .text_selected_range(&self.id, pos, rect, display, range);
    }

    /// Draw an edit marker at the given `byte` index on this `text`
    ///
    /// The text cursor is draw from `rect.pos` and clipped to `rect`.
    ///
    /// The `text` should be prepared before calling this method.
    pub fn text_cursor<T: FormattableText>(
        &mut self,
        pos: Coord,
        rect: Rect,
        text: &Text<T>,
        byte: usize,
    ) {
        if let Ok(text) = text.display() {
            self.h.text_cursor(&self.id, pos, rect, text, byte);
        }
    }

    /// Draw UI element: check box (without label)
    ///
    /// The check box is a small visual element, typically a distinctive square
    /// box with or without a "check" selection mark.
    ///
    /// The theme may animate transitions. To achieve this, `last_change` should be
    /// the time of the last state change caused by the user, or none when the
    /// last state change was programmatic.
    pub fn check_box(&mut self, rect: Rect, checked: bool, last_change: Option<Instant>) {
        self.h.check_box(&self.id, rect, checked, last_change);
    }

    /// Draw UI element: radio box (without label)
    ///
    /// The radio box is a small visual element, typically a disinctive
    /// circular box with or without a "radio" selection mark.
    ///
    /// The theme may animate transitions. To achieve this, `last_change` should be
    /// the time of the last state change caused by the user, or none when the
    /// last state change was programmatic.
    pub fn radio_box(&mut self, rect: Rect, checked: bool, last_change: Option<Instant>) {
        self.h.radio_box(&self.id, rect, checked, last_change);
    }

    /// Draw UI element: mark
    ///
    /// If `rect` is larger than required, the mark will be centered.
    pub fn mark(&mut self, rect: Rect, style: MarkStyle) {
        self.h.mark(&self.id, rect, style);
    }

    /// Draw UI element: scroll bar
    pub fn scroll_bar<W: Tile>(&mut self, track_rect: Rect, grip: &W, dir: Direction) {
        self.h
            .scroll_bar(&self.id, grip.id_ref(), track_rect, grip.rect(), dir);
    }

    /// Draw UI element: slider
    pub fn slider<W: Tile>(&mut self, track_rect: Rect, grip: &W, dir: Direction) {
        self.h
            .slider(&self.id, grip.id_ref(), track_rect, grip.rect(), dir);
    }

    /// Draw UI element: progress bar
    ///
    /// -   `rect`: area of whole widget
    /// -   `dir`: direction of progress bar
    /// -   `state`: highlighting information
    /// -   `value`: progress value, between 0.0 and 1.0
    pub fn progress_bar(&mut self, rect: Rect, dir: Direction, value: f32) {
        self.h.progress_bar(&self.id, rect, dir, value);
    }

    /// Draw an image
    pub fn image(&mut self, rect: Rect, id: ImageId) {
        self.h.image(id, rect);
    }
}

/// Theme drawing implementation
///
/// # Theme extension
///
/// Most themes will not want to implement *everything*, but rather derive
/// not-explicitly-implemented methods from a base theme. This may be achieved
/// with the [`kas::extends`](crate::extends) macro:
/// ```ignore
/// #[extends(ThemeDraw, base = self.base())]
/// impl ThemeDraw {
///     // only implement some methods here
/// }
/// ```
/// Note: [`Self::components`] must be implemented
/// explicitly since this method returns references.
///
/// If Rust had stable specialization + GATs + negative trait bounds we could
/// allow theme extension without macros as follows.
/// <details>
///
/// ```ignore
/// #![feature(generic_associated_types)]
/// #![feature(specialization)]
/// # use kas_core::geom::Rect;
/// # use kas_core::theme::ThemeDraw;
/// /// Provides a default implementation of each theme method over a base theme
/// pub trait ThemeDrawExtends: ThemeDraw {
///     /// Type of base implementation
///     type Base<'a>: ThemeDraw where Self: 'a;
///
///     /// Access the base theme
///     fn base<'a>(&'a mut self) -> Self::Base<'a>;
/// }
///
/// // Note: we may need negative trait bounds here to avoid conflict with impl for Box<H>
/// impl<D: ThemeDrawExtends> ThemeDraw for D {
///     default fn get_clip_rect(&mut self) -> Rect {
///         self.base().get_clip_rect()
///     }
///
///     // And so on for other methods...
/// }
/// ```
/// </details>
#[autoimpl(for<H: trait + ?Sized> Box<H>)]
pub trait ThemeDraw {
    /// Access components: [`ThemeSize`], [`Draw`], [`EventState`]
    fn components(&mut self) -> (&dyn ThemeSize, &mut dyn Draw, &mut EventState);

    /// Access theme colors
    fn colors(&self) -> &ColorsLinear;

    /// Access draw device over [`DrawRounded`] (if available)
    ///
    /// TODO(Rust): remove once Rust supports downcast to trait objects
    fn draw_rounded(&mut self) -> Option<&mut dyn DrawRounded>;

    /// Construct a new pass
    fn new_pass<'a>(
        &mut self,
        rect: Rect,
        offset: Offset,
        class: PassType,
        f: Box<dyn FnOnce(&mut dyn ThemeDraw) + 'a>,
    );

    /// Target area for drawing
    ///
    /// Drawing is restricted to this [`Rect`]. Affected by [`Self::new_pass`].
    /// This may be used to cull hidden items from lists inside a scrollable view.
    fn get_clip_rect(&mut self) -> Rect;

    /// Draw [`EventState`] overlay
    fn event_state_overlay(&mut self);

    /// Draw a frame inside the given `rect`
    ///
    /// The frame dimensions are given by [`ThemeSize::frame`].
    fn frame(&mut self, id: &Id, rect: Rect, style: FrameStyle, bg: Background);

    /// Draw a separator in the given `rect`
    fn separator(&mut self, rect: Rect);

    /// Draw a selection highlight / frame
    fn selection(&mut self, rect: Rect, style: SelectionStyle);

    /// Draw text
    ///
    /// The `text` should be prepared before calling this method.
    fn text(&mut self, id: &Id, pos: Coord, rect: Rect, text: &TextDisplay, color: Option<Rgba>);

    /// Draw text with effects
    ///
    /// [`ThemeDraw::text`] already supports *font* effects: bold,
    /// emphasis, text size. In addition, this method supports underline and
    /// strikethrough effects.
    ///
    /// If `effects` is empty or all [`Effect::flags`] are default then it is
    /// equivalent (and faster) to call [`Self::text`] instead.
    ///
    /// The `text` should be prepared before calling this method.
    fn text_effects(
        &mut self,
        id: &Id,
        pos: Coord,
        rect: Rect,
        text: &TextDisplay,
        colors: &[Rgba],
        effects: &[Effect],
    );

    /// Method used to implement [`DrawCx::text_with_selection`]
    fn text_selected_range(
        &mut self,
        id: &Id,
        pos: Coord,
        rect: Rect,
        text: &TextDisplay,
        range: Range<usize>,
    );

    /// Draw an edit marker at the given `byte` index on this `text`
    ///
    /// The `text` should be prepared before calling this method.
    fn text_cursor(&mut self, id: &Id, pos: Coord, rect: Rect, text: &TextDisplay, byte: usize);

    /// Draw UI element: check box
    ///
    /// The check box is a small visual element, typically a distinctive square
    /// box with or without a "check" selection mark.
    ///
    /// The theme may animate transitions. To achieve this, `last_change` should be
    /// the time of the last state change caused by the user, or none when the
    /// last state change was programmatic.
    fn check_box(&mut self, id: &Id, rect: Rect, checked: bool, last_change: Option<Instant>);

    /// Draw UI element: radio button
    ///
    /// The radio box is a small visual element, typically a disinctive
    /// circular box with or without a "radio" selection mark.
    ///
    /// The theme may animate transitions. To achieve this, `last_change` should be
    /// the time of the last state change caused by the user, or none when the
    /// last state change was programmatic.
    fn radio_box(&mut self, id: &Id, rect: Rect, checked: bool, last_change: Option<Instant>);

    /// Draw UI element: mark
    fn mark(&mut self, id: &Id, rect: Rect, style: MarkStyle);

    /// Draw UI element: scroll bar
    ///
    /// -   `id`: [`Id`] of the bar
    /// -   `grip_id`: [`Id`] of the grip
    /// -   `rect`: area of whole widget (slider track)
    /// -   `grip_rect`: area of slider grip
    /// -   `dir`: direction of bar
    fn scroll_bar(&mut self, id: &Id, grip_id: &Id, rect: Rect, grip_rect: Rect, dir: Direction);

    /// Draw UI element: slider
    ///
    /// -   `id`: [`Id`] of the bar
    /// -   `grip_id`: [`Id`] of the grip
    /// -   `rect`: area of whole widget (slider track)
    /// -   `grip_rect`: area of slider grip
    /// -   `dir`: direction of slider (currently only LTR or TTB)
    fn slider(&mut self, id: &Id, grip_id: &Id, rect: Rect, grip_rect: Rect, dir: Direction);

    /// Draw UI element: progress bar
    ///
    /// -   `id`: [`Id`] of the bar
    /// -   `rect`: area of whole widget
    /// -   `dir`: direction of progress bar
    /// -   `value`: progress value, between 0.0 and 1.0
    fn progress_bar(&mut self, id: &Id, rect: Rect, dir: Direction, value: f32);

    /// Draw an image
    fn image(&mut self, id: ImageId, rect: Rect);
}

#[cfg(test)]
mod test {
    use super::*;

    fn _draw_ext(mut draw: DrawCx) {
        // We can't call this method without constructing an actual ThemeDraw.
        // But we don't need to: we just want to test that methods are callable.

        let _scale = draw.size_cx().scale_factor();

        let text = crate::theme::Text::new("sample", TextClass::Label, false);
        draw.text_with_selection(Coord::ZERO, Rect::ZERO, &text, 0..6)
    }
}