Improve canvas API and fix erasing of multiple elements

src/canvas.rs

@@ -16,7 +16,7 @@
 
 use std::vec::Vec;
 
-use im::Vector;
+use im::{vector, Vector};
 
 use serde::de::{Deserializer, SeqAccess, Visitor};
 use serde::ser::Serializer;
@@ -128,20 +128,43 @@ impl CanvasElement {
             }
         }
     }
-
-    pub fn get_path_mut(&mut self) -> Option<&mut Path> {
-        match self {
-            CanvasElement::Freehand { path, .. } => Some(path),
-        }
-    }
 }
 
 #[derive(Clone, druid::Data)]
 pub struct Canvas {
-    pub elements: Vector<CanvasElement>,
+    elements: Vector<CanvasElement>,
+    content_size: druid::Size,
 }
 
 impl Canvas {
+    pub fn new() -> Self {
+        Canvas {
+            elements: vector![],
+            content_size: druid::Size::new(0.0, 0.0),
+        }
+    }
+
+    pub fn new_with_elements(elements: Vector<CanvasElement>) -> Self {
+        let mut cv = Canvas::new();
+        for e in elements {
+            cv.add_element(e);
+        }
+        cv
+    }
+
+    pub fn add_element(&mut self, element: CanvasElement) {
+        self.content_size = self
+            .content_size
+            .to_rect()
+            .union(element.bounding_box())
+            .size();
+        self.elements.push_back(element);
+    }
+
+    pub fn elements(&self) -> &Vector<CanvasElement> {
+        &self.elements
+    }
+
     /// Find all CanvasElement that intersect with rect
     pub fn find_intersections(&self, rect: druid::Rect) -> Vec<usize> {
         let mut found_elements = Vec::<usize>::new();
@@ -157,6 +180,10 @@ impl Canvas {
 
         found_elements
     }
+
+    pub fn content_size(&self) -> druid::Size {
+        self.content_size
+    }
 }
 
 impl Serialize for Path {

src/main.rs

@@ -49,12 +49,7 @@ pub fn main() {
         color: Color::rgb(255.0, 0.0, 0.0),
     };
     let canvas_data = StilettoState {
-        canvas: CanvasState {
-            versioned_canvas: VersionedCanvas::new(Canvas {
-                elements: vector![],
-            }),
-            tool_ctx: CanvasToolCtx::new(default_pen_params.clone()),
-        },
+        canvas: CanvasState::new(CanvasToolCtx::new(default_pen_params.clone())),
         tool_icons: vector![
             CanvasToolIconState {
                 tool_params: default_pen_params,

src/tool.rs

@@ -91,14 +91,22 @@ impl CanvasToolCtx {
                 self.state = CanvasToolState::Erasing;
             }
             (CanvasToolState::Erasing, Event::MouseMove(mouse_event)) => {
-                let eraser_rect = druid::Rect::from_center_size(mouse_event.pos, (5.0, 5.0));
-                let elements = vcanvas.get().find_intersections(eraser_rect);
-
-                if !elements.is_empty() {
-                    vcanvas.update(|canvas: &mut Canvas| {
-                        for i in elements {
-                            canvas.elements.remove(i);
+                let eraser_rect =
+                    druid::Rect::from_center_size(mouse_event.pos, (5.0, 5.0));
+                let old_elements = vcanvas.get().elements();
+                let mut new_elements = old_elements.clone();
+                new_elements.retain(|elem| {
+                    // Check if the element intersects the eraser rect
+                    if elem.bounding_box().intersect(eraser_rect).area() > 0.0 {
+                        if elem.intersects_rect(eraser_rect) {
+                            return false;
                         }
+                    }
+                    return true;
+                });
+                if new_elements.len() != old_elements.len() {
+                    vcanvas.update(|canvas: &mut Canvas| {
+                        *canvas = Canvas::new_with_elements(new_elements);
                     });
                 }
             }
@@ -138,17 +146,27 @@ impl CanvasToolCtx {
                 },
                 Event::MouseMove(mouse_event),
             ) => {
-                current_path
-                    .get_path_mut()
-                    .unwrap()
-                    .kurbo_path
+                if let CanvasElement::Freehand { ref mut path, .. } = current_path {
+                    path.kurbo_path
                         .line_to((mouse_event.pos.x, mouse_event.pos.y));
                 }
+            }
             (CanvasToolState::DrawingFreehand { .. }, Event::MouseUp(_)) => {
                 vcanvas.update(move |canvas: &mut Canvas| {
                     let current_state = std::mem::replace(&mut self.state, CanvasToolState::Idle);
                     if let CanvasToolState::DrawingFreehand { current_path, .. } = current_state {
-                        canvas.elements.push_back(current_path);
+                        if let CanvasElement::Freehand {
+                            mut path,
+                            mut thickness,
+                            stroke_color,
+                        } = current_path
+                        {
+                            canvas.add_element(CanvasElement::Freehand {
+                                path,
+                                thickness,
+                                stroke_color,
+                            });
+                        }
                     }
                 });
             }

src/widget/canvas.rs

@@ -31,6 +31,12 @@ pub struct CanvasState {
 }
 
 impl CanvasState {
+    pub fn new(tool_ctx: CanvasToolCtx) -> Self {
+        CanvasState {
+            versioned_canvas: VersionedCanvas::new(Canvas::new()),
+            tool_ctx,
+        }
+    }
     pub fn perform_undo(&mut self) {
         //if !self.is_drawing() {
         self.versioned_canvas.undo();
@@ -50,7 +56,7 @@ impl CanvasState {
             canvas_elements: self
                 .versioned_canvas
                 .get()
-                .elements
+                .elements()
                 .iter()
                 .cloned()
                 .collect(),
@@ -58,9 +64,9 @@ impl CanvasState {
     }
 
     pub fn set_from_snapshot(&mut self, snapshot: DocumentSnapshot) {
-        self.versioned_canvas = VersionedCanvas::new(Canvas {
-            elements: Vector::from(snapshot.canvas_elements),
-        });
+        self.versioned_canvas = VersionedCanvas::new(Canvas::new_with_elements(Vector::from(
+            snapshot.canvas_elements,
+        )));
     }
 
     pub fn set_tool_ctx(&mut self, ctx: CanvasToolCtx) {
@@ -128,11 +134,9 @@ impl Widget<CanvasState> for CanvasWidget {
         // (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.versioned_canvas.get().elements.iter() {
+        ctx.fill(rect, &Color::WHITE);
+        for element in data.versioned_canvas.get().elements().iter() {
             element.draw(ctx);
         }
         if data.tool_ctx.needs_repaint() {