Rename CanvasData to CanvasState

src/canvas.rs

@@ -0,0 +1,115 @@
+//  Stiletto
+//  Copyright (C) 2020 Stiletto Authors
+//
+//  This program is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU Affero General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU Affero General Public License for more details.
+//
+//  You should have received a copy of the GNU Affero General Public License
+//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+use im::Vector;
+
+use serde::de::{Deserializer, SeqAccess, Visitor};
+use serde::ser::Serializer;
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, druid::Data)]
+pub struct Path {
+    pub kurbo_path: druid::kurbo::BezPath,
+}
+
+pub type Canvas = Vector<CanvasElement>;
+
+#[derive(Debug, Clone, druid::Data, Serialize, Deserialize)]
+pub enum CanvasElement {
+    Freehand { path: Path, thickness: f64 },
+}
+
+impl CanvasElement {
+    pub fn bounding_box(&self) -> druid::Rect {
+        match self {
+            CanvasElement::Freehand { path, thickness } => {
+                use druid::kurbo::Shape;
+                path.kurbo_path
+                    .bounding_box()
+                    .inflate(*thickness, *thickness)
+            }
+        }
+    }
+    pub fn draw(&self, ctx: &mut druid::PaintCtx) {
+        match self {
+            CanvasElement::Freehand { path, thickness } => {
+                use druid::RenderContext;
+                let stroke_color = druid::Color::rgb8(0, 128, 0);
+                ctx.stroke(&path.kurbo_path, &stroke_color, *thickness);
+            }
+        }
+    }
+
+    pub fn get_path_mut(&mut self) -> Option<&mut Path> {
+        match self {
+            CanvasElement::Freehand { path, .. } => Some(path),
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for Path {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_seq(PathDeserializer)
+    }
+}
+
+impl Serialize for Path {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use druid::kurbo::PathEl;
+
+        serializer.collect_seq(self.kurbo_path.iter().filter_map(|path_el| match path_el {
+            PathEl::MoveTo(pt) => Some(Into::<(f64, f64)>::into(pt)),
+            PathEl::LineTo(pt) => Some(Into::<(f64, f64)>::into(pt)),
+            _ => None,
+        }))
+    }
+}
+
+struct PathDeserializer;
+
+impl<'de> Visitor<'de> for PathDeserializer {
+    type Value = Path;
+
+    fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(formatter, "A sequence of 2D points")
+    }
+
+    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: SeqAccess<'de>,
+    {
+        use druid::kurbo::BezPath;
+
+        let mut kurbo_path = BezPath::new();
+        let mut first_element = true;
+        while let Some(point) = seq.next_element::<(f64, f64)>()? {
+            if first_element {
+                kurbo_path.move_to(point);
+                first_element = false;
+            } else {
+                kurbo_path.line_to(point);
+            }
+        }
+
+        Ok(Path { kurbo_path })
+    }
+}

src/history.rs

@@ -0,0 +1,92 @@
+//  Stiletto
+//  Copyright (C) 2020 Stiletto Authors
+//
+//  This program is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU Affero General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU Affero General Public License for more details.
+//
+//  You should have received a copy of the GNU Affero General Public License
+//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+use super::canvas::Canvas;
+use im::Vector;
+
+#[derive(Clone, druid::Data)]
+pub struct VersionedCanvas {
+    // We internally guarantee that this vector
+    // is never empty
+    versions: Vector<Canvas>,
+    curr_version: usize,
+}
+
+impl VersionedCanvas {
+    pub fn new(canvas: Canvas) -> VersionedCanvas {
+        VersionedCanvas {
+            versions: im::vector![canvas],
+            curr_version: 0,
+        }
+    }
+
+    // Get current canvas version
+    pub fn get(&self) -> &Canvas {
+        self.versions.get(self.curr_version).unwrap()
+    }
+
+    fn has_newer_versions(&self) -> bool {
+        self.curr_version + 1 < self.versions.len()
+    }
+
+    fn has_older_versions(&self) -> bool {
+        self.curr_version > 0
+    }
+
+    pub fn undo(&mut self) {
+        if self.has_older_versions() {
+            self.curr_version = self.curr_version - 1;
+        }
+    }
+
+    pub fn redo(&mut self) {
+        if self.has_newer_versions() {
+            self.curr_version = self.curr_version + 1;
+        }
+    }
+
+    pub fn update(&mut self, update_fn: impl FnOnce(&mut Canvas)) {
+        // Make a new copy of the current canvas version,
+        // so that we can safely modify it without losing
+        // the previous canvas version
+        let mut new_version = self.get().clone();
+        update_fn(&mut new_version);
+
+        // This is a linear history,
+        // so we first check if there are newer versions, if so
+        // this means we are in the past, so a change in the past destroys the future
+        // and creates a new future.
+        if self.has_newer_versions() {
+            self.versions = self.versions.take(self.curr_version + 1);
+        }
+        self.versions.push_back(new_version);
+        self.curr_version = self.curr_version + 1;
+    }
+
+    // Do inplace update, which will be irreversible
+    pub fn irreversible_update(&mut self, update_fn: impl FnOnce(&mut Canvas)) {
+        // Do the update directly on the current canvas version
+        update_fn(self.versions.back_mut().unwrap());
+
+        // This is a linear history,
+        // so we first check if there are newer versions, if so
+        // this means we are in the past, so a change in the past destroys the future
+        // and creates a new future.
+        if self.has_newer_versions() {
+            self.versions = self.versions.take(self.curr_version + 1);
+        }
+    }
+}

src/lib.rs

@@ -12,189 +12,16 @@
 //  GNU Affero General Public License for more details.
 //
 //  You should have received a copy of the GNU Affero General Public License
-//  along with this program.  If not, see <https://www.gnu.org/licenses/>.use serde::{Serialize, Deserialize};
+//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-use im::Vector;
+use serde::{Deserialize, Serialize};
+use std::vec::Vec;
 
-use serde::{Serialize, Deserialize};
-use serde::ser::{Serializer};
-use serde::de::{Deserializer, Visitor, SeqAccess};
-use std::vec::{Vec};
-
-#[derive(Debug, Clone, druid::Data)]
-pub struct Path {
-    pub kurbo_path: druid::kurbo::BezPath,
-}
-
-#[derive(Debug, Clone, druid::Data, Serialize, Deserialize)]
-pub enum CanvasElement {
-    Freehand { path: Path, thickness: f64 },
-}
-
-impl CanvasElement {
-    pub fn bounding_box(&self) -> druid::Rect {
-        match self {
-            CanvasElement::Freehand { path, thickness } => {
-                use druid::kurbo::Shape;
-                path.kurbo_path
-                    .bounding_box()
-                    .inflate(*thickness, *thickness)
-            }
-        }
-    }
-    pub fn draw(&self, ctx: &mut druid::PaintCtx) {
-        match self {
-            CanvasElement::Freehand { path, thickness } => {
-                use druid::RenderContext;
-                let stroke_color = druid::Color::rgb8(0, 128, 0);
-                ctx.stroke(&path.kurbo_path, &stroke_color, *thickness);
-            }
-        }
-    }
-
-    pub fn get_path_mut(&mut self) -> Option<&mut Path> {
-        match self {
-            CanvasElement::Freehand { path, .. } => Some(path),
-        }
-    }
-}
-
-// A canvas contains all elements to be drawn
-pub type Canvas = Vector<CanvasElement>;
-
-#[derive(Clone, druid::Data)]
-pub struct VersionedCanvas {
-    // We internally guarantee that this vector
-    // is never empty
-    versions: Vector<Canvas>,
-    curr_version: usize,
-}
-
-impl VersionedCanvas {
-    pub fn new(canvas: Canvas) -> VersionedCanvas {
-        VersionedCanvas {
-            versions: im::vector![canvas],
-            curr_version: 0,
-        }
-    }
-
-    // Get current canvas version
-    pub fn get(&self) -> &Canvas {
-        self.versions.get(self.curr_version).unwrap()
-    }
-
-    fn has_newer_versions(&self) -> bool {
-        self.curr_version + 1 < self.versions.len()
-    }
-
-    fn has_older_versions(&self) -> bool {
-        self.curr_version > 0
-    }
-
-    pub fn undo(&mut self) {
-        if self.has_older_versions() {
-            self.curr_version = self.curr_version - 1;
-        }
-    }
-
-    pub fn redo(&mut self) {
-        if self.has_newer_versions() {
-            self.curr_version = self.curr_version + 1;
-        }
-    }
-
-    pub fn update(&mut self, update_fn: impl FnOnce(&mut Canvas)) {
-        // Make a new copy of the current canvas version,
-        // so that we can safely modify it without losing
-        // the previous canvas version
-        let mut new_version = self.get().clone();
-        update_fn(&mut new_version);
-
-        // This is a linear history,
-        // so we first check if there are newer versions, if so
-        // this means we are in the past, so a change in the past destroys the future
-        // and creates a new future.
-        if self.has_newer_versions() {
-            self.versions = self.versions.take(self.curr_version + 1);
-        }
-        self.versions.push_back(new_version);
-        self.curr_version = self.curr_version + 1;
-    }
-
-    // Do inplace update, which will be irreversible
-    pub fn irreversible_update(&mut self, update_fn: impl FnOnce(&mut Canvas)) {
-        // Do the update directly on the current canvas version
-        update_fn(self.versions.back_mut().unwrap());
-
-        // This is a linear history,
-        // so we first check if there are newer versions, if so
-        // this means we are in the past, so a change in the past destroys the future
-        // and creates a new future.
-        if self.has_newer_versions() {
-            self.versions = self.versions.take(self.curr_version + 1);
-        }
-    }
-}
-
-struct PathDeserializer;
-
-impl<'de> Visitor<'de> for PathDeserializer {
-    type Value = Path;
-
-    fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
-        write!(formatter, "A sequence of 2D points")
-    }
-
-    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
-    where
-        A: SeqAccess<'de>
-    {
-        use druid::kurbo::BezPath;
-
-        let mut kurbo_path = BezPath::new();
-        let mut first_element = true;
-        while let Some(point) = seq.next_element::<(f64, f64)>()? {
-            if first_element {
-                kurbo_path.move_to(point);
-                first_element = false;
-            } else {
-                kurbo_path.line_to(point);
-            }
-        }
-
-        Ok(Path{ kurbo_path })
-    }
-}
-
-impl<'de> Deserialize<'de> for Path {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>
-    {
-        deserializer.deserialize_seq(PathDeserializer)
-    }
-}
-
-impl Serialize for Path {
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
-    {
-        use druid::kurbo::{PathEl};
-
-        serializer.collect_seq(
-            self.kurbo_path.iter()
-                .filter_map(|path_el| {
-                    match path_el {
-                        PathEl::MoveTo(pt) => Some(Into::<(f64, f64)>::into(pt)),
-                        PathEl::LineTo(pt) => Some(Into::<(f64, f64)>::into(pt)),
-                        _ => None
-                    }
-                }))
-    }
-}
+pub mod canvas;
+pub mod history;
+pub mod widget;
 
 #[derive(Serialize, Deserialize, Debug)]
 pub struct DocumentSnapshot {
-    pub canvas_elements: Vec<CanvasElement>,
+    pub canvas_elements: Vec<canvas::CanvasElement>,
 }

src/main.rs

@@ -16,163 +16,46 @@
 
 use log::{info, warn};
 
-use druid::im::{vector, Vector};
-use druid::kurbo::BezPath;
-use druid::widget::prelude::*;
-use druid::{AppLauncher, Color, Data, Event, LocalizedString, WindowDesc, AppDelegate, Target, Env, DelegateCtx, FileDialogOptions, FileSpec, Command};
 use druid::commands;
+use druid::im::vector;
+use druid::widget::prelude::*;
+use druid::widget::{Align, Button, CrossAxisAlignment, Flex, SizedBox};
+use druid::{
+    AppDelegate, AppLauncher, Command, DelegateCtx, Env, FileDialogOptions, FileSpec,
+    LocalizedString, Target, WindowDesc,
+};
 
-use stiletto::{CanvasElement, VersionedCanvas, Canvas, DocumentSnapshot};
+use stiletto::history::VersionedCanvas;
+use stiletto::widget::{CanvasState, CanvasWidget};
+use stiletto::DocumentSnapshot;
 
-struct Delegate;
-
-#[derive(Clone, Data)]
-struct CanvasData {
-    current_element: Option<CanvasElement>,
-    elements: VersionedCanvas,
+pub fn main() {
+    let window = WindowDesc::new(build_ui)
+        .window_size((1024.0, 1400.0))
+        .title(
+            LocalizedString::new("custom-widget-demo-window-title").with_placeholder("Stiletto"),
+        );
+    let canvas_data = CanvasState {
+        current_element: None,
+        elements: VersionedCanvas::new(vector![]),
+    };
+    AppLauncher::with_window(window)
+        .use_simple_logger()
+        .delegate(Delegate)
+        .launch(canvas_data)
+        .expect("launch failed");
 }
 
-impl CanvasData {
-    fn is_drawing(&self) -> bool {
-        self.current_element.is_some()
-    }
-
-    fn perform_undo(&mut self) {
-        if !self.is_drawing() {
-            self.elements.undo();
-        }
-    }
-
-    fn perform_redo(&mut self) {
-        if !self.is_drawing() {
-            self.elements.redo();
-        }
-    }
-
-    fn get_document_snapshot(&self) -> DocumentSnapshot {
-        DocumentSnapshot {
-            canvas_elements: self.elements.get().iter().cloned().collect()
-        }
-    }
-
-    fn set_from_snapshot(&mut self, snapshot: DocumentSnapshot) {
-        self.current_element = None;
-        self.elements = VersionedCanvas::new(Vector::from(snapshot.canvas_elements));
-    }
-}
-
-struct CanvasWidget;
-
-impl Widget<CanvasData> for CanvasWidget {
-    fn event(&mut self, _ctx: &mut EventCtx, event: &Event, data: &mut CanvasData, _env: &Env) {
-        match event {
-            Event::MouseDown(mouse_event) => {
-                let mut kurbo_path = BezPath::new();
-                kurbo_path.move_to((mouse_event.pos.x, mouse_event.pos.y));
-                data.current_element = Some(CanvasElement::Freehand {
-                    path: stiletto::Path { kurbo_path },
-                    thickness: 2.0,
-                });
-            }
-            Event::MouseMove(mouse_event) => {
-                if data.is_drawing() {
-                    if let Some(current_element) = data.current_element.as_mut() {
-                        current_element
-                            .get_path_mut()
-                            .unwrap()
-                            .kurbo_path
-                            .line_to((mouse_event.pos.x, mouse_event.pos.y));
-                    }
-                }
-            }
-            Event::MouseUp(_) => {
-                if data.is_drawing() {
-                    if let Some(current_element) = data.current_element.take() {
-
-                        data.elements.update(move |canvas: &mut Canvas| {
-                            canvas.push_back(current_element);
-                        });
-
-                    }
-                }
-            }
-            _ => {}
-        }
-    }
-
-    fn lifecycle(
-        &mut self,
-        _ctx: &mut LifeCycleCtx,
-        _event: &LifeCycle,
-        _data: &CanvasData,
-        _env: &Env,
-    ) {
-    }
-
-    fn update(
-        &mut self,
-        ctx: &mut UpdateCtx,
-        old_data: &CanvasData,
-        data: &CanvasData,
-        _env: &Env,
-    ) {
-        // the current_element is moved to the elements array, no need to repaint
-        if old_data.is_drawing() && !data.is_drawing() {
-            return;
-        }
-        if data.is_drawing() {
-            if let Some(e) = data.current_element.as_ref() {
-                ctx.request_paint_rect(e.bounding_box());
-            }
-        } else {
-            ctx.request_paint();
-        }
-    }
-
-    fn layout(
-        &mut self,
-        _layout_ctx: &mut LayoutCtx,
-        bc: &BoxConstraints,
-        _data: &CanvasData,
-        _env: &Env,
-    ) -> Size {
-        // BoxConstraints are passed by the parent widget.
-        // This method can return any Size within those constraints:
-        // bc.constrain(my_size)
-        //
-        // To check if a dimension is infinite or not (e.g. scrolling):
-        // bc.is_width_bounded() / bc.is_height_bounded()
-        bc.max()
-    }
-
-    // The paint method gets called last, after an event flow.
-    // It goes event -> update -> layout -> paint, and each method can influence the next.
-    // Basically, anything that changes the appearance of a widget causes a paint.
-    fn paint(&mut self, ctx: &mut PaintCtx, data: &CanvasData, _env: &Env) {
-        // (ctx.size() returns the size of the layout rect we're painting in)
-        let size = ctx.size();
-        let rect = size.to_rect();
-        // Note: ctx also has a `clear` method, but that clears the whole context,
-        // and we only want to clear this widget's area.
-        ctx.fill(rect, &Color::WHITE);
-
-        for element in data.elements.get().iter() {
-            element.draw(ctx);
-        }
-        if let Some(element) = &data.current_element {
-            element.draw(ctx);
-        }
-    }
-}
-
-fn build_ui() -> impl Widget<CanvasData> {
-    use druid::widget::{Align, Button, CrossAxisAlignment, Flex, SizedBox};
-    let history_buttons = Flex::row()
-        .cross_axis_alignment(CrossAxisAlignment::Center)
-        .with_child(
-            Button::new("Undo").on_click(|_ctx: &mut EventCtx, data: &mut CanvasData, _env: &Env| data.perform_undo())
-        )
-        .with_child(Button::new("Redo").on_click(|_ctx: &mut EventCtx, data: &mut CanvasData, _env: &Env| data.perform_redo()));
+fn build_ui() -> impl Widget<CanvasState> {
+    let history_buttons =
+        Flex::row()
+            .cross_axis_alignment(CrossAxisAlignment::Center)
+            .with_child(Button::new("Undo").on_click(
+                |_ctx: &mut EventCtx, data: &mut CanvasState, _env: &Env| data.perform_undo(),
+            ))
+            .with_child(Button::new("Redo").on_click(
+                |_ctx: &mut EventCtx, data: &mut CanvasState, _env: &Env| data.perform_redo(),
+            ));
 
     let stlt = FileSpec::new("Stiletto notebook", &["stlt"]);
     let save_dialog_options = FileDialogOptions::new()
@@ -182,29 +65,24 @@ fn build_ui() -> impl Widget<CanvasData> {
 
     let save_buttons = Flex::row()
         .cross_axis_alignment(CrossAxisAlignment::Center)
-        .with_child(
-            Button::new("Open")
-                .on_click(move |ctx, _, _| {
-                    ctx.submit_command(
-                        Command::new(
-                            druid::commands::SHOW_OPEN_PANEL,
-                            open_dialog_options.clone(),
-                        ),
-                        None,
-                    )
-                }))
-        .with_child(
-            Button::new("Save")
-                .on_click(move |ctx, _, _| {
-                    ctx.submit_command(
-                        Command::new(
-                            druid::commands::SHOW_SAVE_PANEL,
-                            save_dialog_options.clone(),
-                        ),
-                        None,
-                    )
-                }));
-
+        .with_child(Button::new("Open").on_click(move |ctx, _, _| {
+            ctx.submit_command(
+                Command::new(
+                    druid::commands::SHOW_OPEN_PANEL,
+                    open_dialog_options.clone(),
+                ),
+                None,
+            )
+        }))
+        .with_child(Button::new("Save").on_click(move |ctx, _, _| {
+            ctx.submit_command(
+                Command::new(
+                    druid::commands::SHOW_SAVE_PANEL,
+                    save_dialog_options.clone(),
+                ),
+                None,
+            )
+        }));
 
     let toolbar = Flex::row()
         .cross_axis_alignment(CrossAxisAlignment::Center)
@@ -220,30 +98,15 @@ fn build_ui() -> impl Widget<CanvasData> {
         .with_flex_child(CanvasWidget {}, 1.0)
 }
 
-pub fn main() {
-    let window = WindowDesc::new(build_ui)
-        .window_size((1024.0, 1400.0))
-        .title(
-            LocalizedString::new("custom-widget-demo-window-title").with_placeholder("Stiletto"),
-        );
-    let canvas_data = CanvasData {
-        current_element: None,
-        elements: VersionedCanvas::new(vector![]),
-    };
-    AppLauncher::with_window(window)
-        .use_simple_logger()
-        .delegate(Delegate)
-        .launch(canvas_data)
-        .expect("launch failed");
-}
+struct Delegate;
 
-impl AppDelegate<CanvasData> for Delegate {
+impl AppDelegate<CanvasState> for Delegate {
     fn command(
         &mut self,
         _ctx: &mut DelegateCtx,
         _target: Target,
         cmd: &Command,
-        data: &mut CanvasData,
+        data: &mut CanvasState,
         _env: &Env,
     ) -> bool {
         use std::fs::File;
@@ -264,7 +127,8 @@ impl AppDelegate<CanvasData> for Delegate {
         }
         if let Some(file_info) = cmd.get(commands::OPEN_FILE) {
             if let Ok(f) = File::open(file_info.path()) {
-                let res_snapshot: Result<DocumentSnapshot, serde_json::Error> = serde_json::from_reader(f);
+                let res_snapshot: Result<DocumentSnapshot, serde_json::Error> =
+                    serde_json::from_reader(f);
                 if let Ok(document_snapshot) = res_snapshot {
                     data.set_from_snapshot(document_snapshot);
                     info!("Loaded file {}", file_info.path().display());

src/widget.rs

@@ -0,0 +1,163 @@
+//  Stiletto
+//  Copyright (C) 2020 Stiletto Authors
+//
+//  This program is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU Affero General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU Affero General Public License for more details.
+//
+//  You should have received a copy of the GNU Affero General Public License
+//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+use im::Vector;
+
+use super::canvas;
+use super::canvas::{Canvas, CanvasElement};
+use super::history::VersionedCanvas;
+use super::DocumentSnapshot;
+
+use druid::kurbo::BezPath;
+use druid::widget::prelude::*;
+use druid::{Color, Data, Env, Event};
+
+#[derive(Clone, Data)]
+pub struct CanvasState {
+    pub current_element: Option<CanvasElement>,
+    pub elements: VersionedCanvas,
+}
+
+impl CanvasState {
+    pub fn is_drawing(&self) -> bool {
+        self.current_element.is_some()
+    }
+
+    pub fn perform_undo(&mut self) {
+        if !self.is_drawing() {
+            self.elements.undo();
+        }
+    }
+
+    pub fn perform_redo(&mut self) {
+        if !self.is_drawing() {
+            self.elements.redo();
+        }
+    }
+
+    pub fn get_document_snapshot(&self) -> DocumentSnapshot {
+        DocumentSnapshot {
+            canvas_elements: self.elements.get().iter().cloned().collect(),
+        }
+    }
+
+    pub fn set_from_snapshot(&mut self, snapshot: DocumentSnapshot) {
+        self.current_element = None;
+        self.elements = VersionedCanvas::new(Vector::from(snapshot.canvas_elements));
+    }
+}
+
+pub struct CanvasWidget;
+
+impl Widget<CanvasState> for CanvasWidget {
+    fn event(&mut self, _ctx: &mut EventCtx, event: &Event, data: &mut CanvasState, _env: &Env) {
+        match event {
+            Event::MouseDown(mouse_event) => {
+                let mut kurbo_path = BezPath::new();
+                kurbo_path.move_to((mouse_event.pos.x, mouse_event.pos.y));
+                data.current_element = Some(CanvasElement::Freehand {
+                    path: canvas::Path { kurbo_path },
+                    thickness: 2.0,
+                });
+            }
+            Event::MouseMove(mouse_event) => {
+                if data.is_drawing() {
+                    if let Some(current_element) = data.current_element.as_mut() {
+                        current_element
+                            .get_path_mut()
+                            .unwrap()
+                            .kurbo_path
+                            .line_to((mouse_event.pos.x, mouse_event.pos.y));
+                    }
+                }
+            }
+            Event::MouseUp(_) => {
+                if data.is_drawing() {
+                    if let Some(current_element) = data.current_element.take() {
+                        data.elements.update(move |canvas: &mut Canvas| {
+                            canvas.push_back(current_element);
+                        });
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn lifecycle(
+        &mut self,
+        _ctx: &mut LifeCycleCtx,
+        _event: &LifeCycle,
+        _data: &CanvasState,
+        _env: &Env,
+    ) {
+    }
+
+    fn update(
+        &mut self,
+        ctx: &mut UpdateCtx,
+        old_data: &CanvasState,
+        data: &CanvasState,
+        _env: &Env,
+    ) {
+        // the current_element is moved to the elements array, no need to repaint
+        if old_data.is_drawing() && !data.is_drawing() {
+            return;
+        }
+        if data.is_drawing() {
+            if let Some(e) = data.current_element.as_ref() {
+                ctx.request_paint_rect(e.bounding_box());
+            }
+        } else {
+            ctx.request_paint();
+        }
+    }
+
+    fn layout(
+        &mut self,
+        _layout_ctx: &mut LayoutCtx,
+        bc: &BoxConstraints,
+        _data: &CanvasState,
+        _env: &Env,
+    ) -> Size {
+        // BoxConstraints are passed by the parent widget.
+        // This method can return any Size within those constraints:
+        // bc.constrain(my_size)
+        //
+        // To check if a dimension is infinite or not (e.g. scrolling):
+        // bc.is_width_bounded() / bc.is_height_bounded()
+        bc.max()
+    }
+
+    // The paint method gets called last, after an event flow.
+    // It goes event -> update -> layout -> paint, and each method can influence the next.
+    // Basically, anything that changes the appearance of a widget causes a paint.
+    fn paint(&mut self, ctx: &mut PaintCtx, data: &CanvasState, _env: &Env) {
+        // (ctx.size() returns the size of the layout rect we're painting in)
+        let size = ctx.size();
+        let rect = size.to_rect();
+        // Note: ctx also has a `clear` method, but that clears the whole context,
+        // and we only want to clear this widget's area.
+        ctx.fill(rect, &Color::WHITE);
+
+        for element in data.elements.get().iter() {
+            element.draw(ctx);
+        }
+        if let Some(element) = &data.current_element {
+            element.draw(ctx);
+        }
+    }
+}