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use smallvec::smallvec;
use std::mem::replace;

use crate::draw::*;
use crate::event::{Event, Key};
use crate::layout::{Rectangle, Size};
use crate::stylesheet::{StyleState, Stylesheet};
use crate::widget::{Context, IntoNode, Node, StateVec, Widget};

/// A clickable button
pub struct Button<'a, T> {
    state: &'a mut State,
    content: Node<'a, T>,
    on_clicked: Option<T>,
}

/// State for [`Button`](struct.Button.html)
#[allow(missing_docs)]
pub enum State {
    Idle,
    Hover,
    Pressed,
    Disabled,
}

impl<'a, T: 'a> Button<'a, T> {
    /// Construct a new button
    pub fn new<C: IntoNode<'a, T> + 'a>(state: &'a mut State, content: C) -> Self {
        Self {
            state,
            content: content.into_node(),
            on_clicked: None,
        }
    }

    /// Sets the message to be posted when this button is clicked.
    pub fn on_clicked(mut self, message: T) -> Self {
        self.on_clicked = Some(message);
        self
    }
}

impl<'a, T: 'a + Send> Widget<'a, T> for Button<'a, T> {
    fn widget(&self) -> &'static str {
        "button"
    }

    fn state(&self) -> StateVec {
        match self.state {
            State::Idle => StateVec::new(),
            State::Hover => smallvec![StyleState::Hover],
            State::Pressed => smallvec![StyleState::Pressed],
            State::Disabled => smallvec![StyleState::Disabled],
        }
    }

    fn len(&self) -> usize {
        1
    }

    fn visit_children(&mut self, visitor: &mut dyn FnMut(&mut Node<'a, T>)) {
        visitor(&mut self.content);
    }

    fn size(&self, style: &Stylesheet) -> (Size, Size) {
        style
            .background
            .resolve_size((style.width, style.height), self.content.size(), style.padding)
    }

    fn event(&mut self, layout: Rectangle, clip: Rectangle, _: &Stylesheet, event: Event, context: &mut Context<T>) {
        match event {
            Event::Cursor(x, y) => {
                *self.state = match replace(self.state, State::Idle) {
                    State::Idle => {
                        if layout.point_inside(x, y) && clip.point_inside(x, y) {
                            context.redraw();
                            State::Hover
                        } else {
                            State::Idle
                        }
                    }
                    State::Hover => {
                        if layout.point_inside(x, y) && clip.point_inside(x, y) {
                            State::Hover
                        } else {
                            context.redraw();
                            State::Idle
                        }
                    }
                    State::Pressed => {
                        if layout.point_inside(x, y) && clip.point_inside(x, y) {
                            State::Pressed
                        } else {
                            context.redraw();
                            State::Idle
                        }
                    }
                    State::Disabled => State::Disabled,
                };
            }

            Event::Press(Key::LeftMouseButton) => {
                *self.state = match replace(self.state, State::Idle) {
                    State::Hover => {
                        context.redraw();
                        State::Pressed
                    }
                    other => other,
                };
            }

            Event::Release(Key::LeftMouseButton) => {
                *self.state = match replace(self.state, State::Idle) {
                    State::Pressed => {
                        context.redraw();
                        context.extend(self.on_clicked.take());
                        State::Hover
                    }
                    other => other,
                };
            }

            _ => (),
        }
    }

    fn draw(&mut self, layout: Rectangle, clip: Rectangle, style: &Stylesheet) -> Vec<Primitive<'a>> {
        let content_rect = style.background.content_rect(layout, style.padding);

        style
            .background
            .render(layout)
            .into_iter()
            .chain(self.content.draw(content_rect, clip).into_iter())
            .collect()
    }
}

impl<'a, T: 'a + Send> IntoNode<'a, T> for Button<'a, T> {
    fn into_node(self) -> Node<'a, T> {
        Node::new(self)
    }
}

impl Default for State {
    fn default() -> Self {
        State::Idle
    }
}