Conditional Views

If you try something like this:

#![allow(unused)]
fn main() {
extern crate buoyant;
extern crate embedded_graphics;
use buoyant::view::prelude::*;
use embedded_graphics::{mono_font::ascii::FONT_9X15, pixelcolor::Rgb888};

fn view(is_redacted: bool) -> impl View<Rgb888, ()> {
    if is_redacted {
        Rectangle
    } else {
        Text::new("This is visible!", &FONT_9X15)
    }
}
}

You’ll of course get an error telling you that the types returned from each branch don’t match.

Buoyant provides two macros for creating content conditionally.

Conditional Views with if_view!

The if_view! macro allows you to write views as if you were writing a plain if statement.

extern crate buoyant;
extern crate embedded_graphics;
extern crate embedded_graphics_simulator;
use embedded_graphics_simulator::{OutputSettings, SimulatorDisplay, Window};

const BACKGROUND_COLOR: Rgb888 = Rgb888::CSS_DARK_SLATE_GRAY;
const DEFAULT_COLOR: Rgb888 = Rgb888::WHITE;

fn main() {
    let mut window = Window::new("Example", &OutputSettings::default());
    let mut display: SimulatorDisplay<Rgb888> = SimulatorDisplay::new(Size::new(480, 320));

    display.clear(BACKGROUND_COLOR).unwrap();

    view()
        .as_drawable(display.size(), DEFAULT_COLOR, &mut ())
        .draw(&mut display)
        .unwrap();

    window.show_static(&display);
}

use buoyant::if_view;
use buoyant::view::prelude::*;
use embedded_graphics::{mono_font::ascii::FONT_9X15, pixelcolor::Rgb888, prelude::*};

fn secret_message(message: &str, is_redacted: bool) -> impl View<Rgb888, ()> + use<'_> {
    if_view!((is_redacted) {
        RoundedRectangle::new(4)
            .frame()
            .with_width(9 * message.len() as u32) // yeah yeah ignoring UTF8
            .with_height(15)
    } else {
        Text::new(message, &FONT_9X15)
    })
}

fn view() -> impl View<Rgb888, ()> {
    VStack::new((
        secret_message("Top secret message", true),
        secret_message("Hi Mom!", false),
        secret_message("hunter12", true),
        secret_message("Cats are cool", false),
    ))
    .with_spacing(10)
    .with_alignment(buoyant::layout::HorizontalAlignment::Leading)
    .padding(Edges::All, 10)
}

Variable Binding with match_view!

The match_view! macro is a more powerful version of if_view! that allows you to bind variables in the match arms.

extern crate buoyant;
extern crate embedded_graphics;
extern crate embedded_graphics_simulator;
use embedded_graphics_simulator::{OutputSettings, SimulatorDisplay, Window};

const BACKGROUND_COLOR: Rgb888 = Rgb888::CSS_DARK_SLATE_GRAY;
const DEFAULT_COLOR: Rgb888 = Rgb888::WHITE;

fn main() {
    let mut window = Window::new("Example", &OutputSettings::default());
    let mut display: SimulatorDisplay<Rgb888> = SimulatorDisplay::new(Size::new(480, 320));

    display.clear(BACKGROUND_COLOR).unwrap();

    view()
        .as_drawable(display.size(), DEFAULT_COLOR, &mut ())
        .draw(&mut display)
        .unwrap();

    window.show_static(&display);
}

use buoyant::match_view;
use buoyant::view::prelude::*;
use embedded_graphics::{pixelcolor::Rgb888, prelude::*};

#[derive(Debug, Clone, Copy)]
enum Shape {
    Rectangle,
    RoundedRect(u16),
    None,
}

fn shape(shape: Shape) -> impl View<Rgb888, ()> {
    match_view!(shape, {
        Shape::Rectangle => {
            Rectangle
        },
        Shape::RoundedRect(radius) => {
            RoundedRectangle::new(radius)
        },
        Shape::None => {
            EmptyView
        }
    })
}

fn view() -> impl View<Rgb888, ()> {
    VStack::new((
        shape(Shape::Rectangle)
            .foreground_color(Rgb888::CSS_PALE_GREEN),
        shape(Shape::RoundedRect(10))
            .foreground_color(Rgb888::CSS_MEDIUM_ORCHID),
        shape(Shape::None)
            .foreground_color(Rgb888::WHITE),
        shape(Shape::RoundedRect(30))
            .foreground_color(Rgb888::CSS_INDIAN_RED),
    ))
    .with_spacing(10)
    .padding(Edges::All, 10)
}

Maintaining Consistent Spacing with EmptyView

Notice how despite returning a view for the Shape::None variant above, the correct spacing remains between its neighbors. EmptyView is useful when you must return a view, but don’t want anything to be rendered and don’t want to disrupt stack spacing.

Not all modifiers will transfer this spacing behavior when applied to an EmptyView.

When an if_view! does not specify an else, EmptyView is implied for the else branch.

#![allow(unused)]
fn main() {
extern crate buoyant;
extern crate embedded_graphics;
use embedded_graphics::pixelcolor::Rgb888;
use embedded_graphics::mono_font::ascii::FONT_9X15;
use buoyant::view::prelude::*;
use buoyant::if_view;

/// A rectangle if not hidden, otherwise implicit `EmptyView`
fn maybe_rectangle(hidden: bool) -> impl View<Rgb888, ()> {
    if_view!((!hidden) {
        Rectangle
    })
}
}