How to create a table of custom shapes in iced (Rust GUI framework)?
I'm trying to create a GUI for a board game engine. To that end I'm trying to transform the State (A struct with a grid where game pieces can be) into a rendered grid. I decided to try and do this with Iced, but I'm having trouble getting a custom shape into the grid structures in Iced. I should add that I'm pretty new to rust in general, and so my problems might not be with understanding Iced specifically.
I tried a few approaches, mainly these:
Implement the custom widget trait for the octagon, based on the
custom_widgetexample from the Iced repository. I did not keep the code I used for this attempt, but at some point I realized (I think) that Iced has two classes of widgets, built-in and custom, where the custom ones do not promise full widget behavior and the built-in ones are harder to implement.Try to encapsulate the struct in a Canvas widget, and implement
canvas::Program<Message>with my owndrawfunction.
Both of these resulted in a similar compilation error, when writing the view function for my implementation of Application:
fn view(&self) -> iced::Element<'_, Self::Message> {
let matrix = self.get_board();
let mut base = Column::new().padding(20).spacing(20);
for row in matrix {
let mut gui_row = Row::new().padding(20).spacing(20);
for value in row {
// ...get details about the specific piece in
// this cell
let oct = crate::gui::octagon::Octagon::new(30.);
// this is the line I want to change, and push a custom
// struct with an octagonal shape instead of a button
gui_row = gui_row.push(Button::new("Pushing a button works"));
}
base = base.push(gui_row);
}
base.into()
}
Where I get the following:
the trait bound `iced::advanced::iced_graphics::iced_core::Element<'_, (), iced_renderer::Renderer<Theme>>: From<Column<'_, Message>>` is not satisfied
the following other types implement trait `From<T>`:
<iced::advanced::iced_graphics::iced_core::Element<'a, Message, Renderer> as From<Column<'a, Message, Renderer>>>
<iced::advanced::iced_graphics::iced_core::Element<'a, Message, Renderer> as From<MouseArea<'a, Message, Renderer>>>
<iced::advanced::iced_graphics::iced_core::Element<'a, Message, Renderer> as From<Row<'a, Message, Renderer>>>
<iced::advanced::iced_graphics::iced_core::Element<'a, Message, Renderer> as From<iced::widget::Button<'a, Message, Renderer>>>
<iced::advanced::iced_graphics::iced_core::Element<'a, Message, Renderer> as From<iced::widget::Checkbox<'a, Message, Renderer>>>
<iced::advanced::iced_graphics::iced_core::Element<'a, Message, Renderer> as From<ComboBox<'a, T, Message, Renderer>>>
<iced::advanced::iced_graphics::iced_core::Element<'a, Message, Renderer> as From<iced::widget::Container<'a, Message, Renderer>>>
<iced::advanced::iced_graphics::iced_core::Element<'a, Message, Renderer> as From<menu::List<'a, T, Message, Renderer>>>
and 15 others
required for `Column<'_, Message>` to implement `Into<iced::advanced::iced_graphics::iced_core::Element<'_, (), iced_renderer::Renderer<Theme>>>`
A minimal(ish) reproduceable example:
use iced::widget::{Canvas, Column, Row, Button};
use iced::{executor, Color, Application, Command, Settings, Theme};
#[derive(Copy, Clone)]
struct Piece; // some sort of Octagon
struct State {
board: [[Option<Piece>; 4]; 4]
}
impl Application for State {
type Executor = executor::Default;
type Flags = ();
type Message = ();
type Theme = Theme;
fn new(_flags: ()) -> (State, Command<Self::Message>) {
(State {board: [[None; 4]; 4]}, Command::none())
}
fn title(&self) -> String {
String::from("A cool application")
}
fn update(&mut self, _message: Self::Message) -> Command<Self::Message> {
Command::none()
}
fn view(&self) -> iced::Element<'_, Self::Message> {
let matrix = self.board;
let mut base = Column::new().padding(20).spacing(20);
for row in matrix {
let mut gui_row = Row::new().padding(20).spacing(20);
for value in row {
let color = match value {
Some(piece) => Color::BLACK,
None => Color::WHITE,
};
let oct = crate::octagon::Octagon::new(30.);
gui_row = gui_row.push(Canvas::new(oct));
}
base = base.push(gui_row);
}
base.into()
}
}
pub fn main() -> iced::Result {
State::run(Settings::default())
}
mod octagon {
use iced::{Rectangle, mouse, Renderer, Theme, Point, widget};
use iced::widget::{canvas, container};
use iced::widget::canvas::{Event, event, Cache, Path};
pub enum Message {
None
}
pub struct Octagon {
size: f32,
cache: Cache
}
impl Octagon {
pub fn new(size: f32) -> Octagon{
Octagon {size: size, cache: Cache::new()}
}
}
impl canvas::Program<Message> for Octagon {
type State = ();
fn update(
&self,
_state: &mut Self::State,
event: Event,
bounds: Rectangle,
cursor: mouse::Cursor,
) -> (event::Status, Option<Message>) {
todo!()
}
fn draw(
&self,
_state: &Self::State,
renderer: &Renderer,
_theme: &Theme,
bounds: Rectangle,
_cursor: mouse::Cursor,
) -> Vec<canvas::Geometry> {
let geom = self.cache.draw(renderer, bounds.size(), |frame| {
// this is not an octagon, but it's some sort
// of geometric shape that I can't render
frame.stroke(
&Path::new(|builder| {
builder.line_to(Point { x: 0., y: 0. });
builder.line_to(Point { x: 206., y: 131. });
builder.line_to(Point { x: 9., y: 699. });
builder.close();
}),
canvas::Stroke::default(),
);
});
vec![geom]
}
}
}
Solution
You are very close already.
- The
Messageenum must be exported (so that it can be used as an Associated Type in theApplicationimplmentation) and implementDebug(it must implementDebug, because of this trait bound):
#[derive(Debug)]
pub(crate) enum Message {
None,
}
Use the
Messageenum from theoctagonmodule in yourApplicationimplementation:type Message = octagon::Message;This is not needed for compilation but otherwise the program will
panicat runtime. Change theupdatefunction of thecanvas::Program<Message>implementation, to for example:
fn update(
&self,
_state: &mut Self::State,
event: Event,
bounds: Rectangle,
cursor: mouse::Cursor,
) -> (Status, Option<Message>) {
(Status::Ignored, None)
}
Here is the full fixed sample:
use iced::widget::{Canvas, Column, Row};
use iced::{executor, Application, Color, Command, Settings, Theme};
#[derive(Copy, Clone)]
struct Piece; // some sort of Octagon
struct State {
board: [[Option<Piece>; 4]; 4],
}
impl Application for State {
type Executor = executor::Default;
type Flags = ();
type Message = octagon::Message;
type Theme = Theme;
fn new(_flags: ()) -> (State, Command<Self::Message>) {
(
State {
board: [[None; 4]; 4],
},
Command::none(),
)
}
fn title(&self) -> String {
String::from("A cool application")
}
fn update(&mut self, _message: Self::Message) -> Command<Self::Message> {
Command::none()
}
fn view(&self) -> iced::Element<Self::Message> {
let matrix = self.board;
let mut base = Column::new().padding(20).spacing(20);
for row in matrix {
let mut gui_row = Row::new().padding(20).spacing(20);
for value in row {
let color = match value {
Some(piece) => Color::BLACK,
None => Color::WHITE,
};
let oct = crate::octagon::Octagon::new(30.);
gui_row = gui_row.push(Canvas::new(oct));
}
base = base.push(gui_row);
}
base.into()
}
}
pub fn main() -> iced::Result {
State::run(Settings::default())
}
mod octagon {
use iced::event::Status;
use iced::widget::canvas;
use iced::widget::canvas::{Cache, Event, Path};
use iced::{mouse, Point, Rectangle, Renderer, Theme};
#[derive(Debug)]
pub(crate) enum Message {
None,
}
pub struct Octagon {
size: f32,
cache: Cache,
}
impl Octagon {
pub fn new(size: f32) -> Octagon {
Octagon {
size: size,
cache: Cache::new(),
}
}
}
impl canvas::Program<Message> for Octagon {
type State = ();
fn update(
&self,
_state: &mut Self::State,
event: Event,
bounds: Rectangle,
cursor: mouse::Cursor,
) -> (Status, Option<Message>) {
(Status::Ignored, None)
}
fn draw(
&self,
_state: &Self::State,
renderer: &Renderer,
_theme: &Theme,
bounds: Rectangle,
_cursor: mouse::Cursor,
) -> Vec<canvas::Geometry> {
let geom = self.cache.draw(renderer, bounds.size(), |frame| {
// this is not an octagon, but it's some sort
// of geometric shape that I can't render
frame.stroke(
&Path::new(|builder| {
builder.line_to(Point { x: 0., y: 0. });
builder.line_to(Point { x: 206., y: 131. });
builder.line_to(Point { x: 9., y: 699. });
builder.close();
}),
canvas::Stroke::default(),
);
});
vec![geom]
}
}
}
Giving you this output:
If you want to render actual octagons you can change the draw function to:
fn draw(
&self,
_state: &Self::State,
renderer: &Renderer,
_theme: &Theme,
bounds: Rectangle,
_cursor: mouse::Cursor,
) -> Vec<canvas::Geometry> {
let geom = self.cache.draw(renderer, bounds.size(), |frame| {
frame.stroke(
&Path::new(|builder| {
let r = 50.;
for i in 0..8 {
let angle_rad = 360. / 8. * i as f32 * std::f32::consts::PI / 180.;
builder.line_to(Point {
x: angle_rad.cos() * r + r,
y: angle_rad.sin() * r + r,
});
}
builder.close();
}),
canvas::Stroke::default(),
);
});
vec![geom]
}
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