Add basic eraser

src/handwriting/mod.rs

@@ -1,5 +1,6 @@
 mod canvas_rasterizer;
 mod disk_format;
+mod tool;
 
 use std::{
     fmt::{self, Display},
@@ -21,12 +22,13 @@ use egui::{
 use eyre::{Context, bail};
 use eyre::{OptionExt, eyre};
 use half::f16;
-use serde::Serialize;
 use zerocopy::{FromBytes, IntoBytes};
 
 use crate::{custom_code_block::try_from_custom_code_block, rasterizer};
 use crate::{custom_code_block::write_custom_code_block, util::random_id};
 
+use self::tool::{ToolEvent, Tool};
+
 const HANDWRITING_MIN_HEIGHT: f32 = 100.0;
 const HANDWRITING_BOTTOM_PADDING: f32 = 80.0;
 const HANDWRITING_MARGIN: f32 = 0.05;
@@ -79,6 +81,14 @@ struct Ephemeral {
 
     canvas_rasterizer: CanvasRasterizer,
 
+    tool: Tool,
+
+    /// Tool position in canvas space.
+    tool_position: Option<Pos2>,
+
+    /// Tool position last frame, in canvas space.
+    last_tool_position: Option<Pos2>,
+
     /// The stroke that is currently being drawed.
     current_stroke: Vec<Pos2>,
 
@@ -129,6 +139,9 @@ impl Default for Ephemeral {
         Self {
             id: random_id(),
             canvas_rasterizer: Default::default(),
+            tool: Tool::Eraser,
+            tool_position: None,
+            last_tool_position: None,
             current_stroke: Default::default(),
             tessellator: None,
             mesh: Default::default(),
@@ -173,6 +186,14 @@ impl Handwriting {
                 let _ = Clipboard::new().unwrap().set_text(text);
             }
 
+            let (label, switch_to_tool) = match self.e.tool {
+                Tool::Pencil => ("eraser", Tool::Eraser),
+                Tool::Eraser => ("pencil", Tool::Pencil),
+            };
+            if ui.button(label).clicked() {
+                self.e.tool = switch_to_tool;
+            }
+
             let vertex_count: usize = self.e.mesh.indices.len() / 3;
             ui.label(format!("vertices: {vertex_count}"));
         })
@@ -212,6 +233,8 @@ impl Handwriting {
             emath::RectTransform::from_to(Rect::from_min_size(Pos2::ZERO, size), response.rect);
         let from_screen = to_screen.inverse();
 
+        self.e.last_tool_position = self.e.tool_position;
+
         // Was the user in the process of drawing a stroke last frame?
         let was_drawing = !self.e.current_stroke.is_empty();
 
@@ -271,10 +294,21 @@ impl Handwriting {
 
             // Process input events and turn them into strokes
             for event in events {
-                let mut last_canvas_pos = self.e.current_stroke.last().copied();
+                let mut last_tool_position = self.e.last_tool_position;
-                process_event(&mut last_canvas_pos, from_screen, &event, |tool_event| {
+                process_event(&mut last_tool_position, from_screen, &event, |tool_event| {
-                    if self.on_tool_event(tool_event) {
+                    self.e.tool_position = tool_event.position();
-                        hw_response.changed = true; // FIXME: ugly
+                    match self.e.tool {
+                        Tool::Pencil => {
+                            hw_response.changed |=
+                            tool::pencil::on_tool_event(self, tool_event);
+                            
+                        }
+                        Tool::Eraser => {
+                            if tool::eraser::on_tool_event(self, tool_event) {
+                                self.e.refresh_texture = true;
+                                hw_response.changed = true;
+                            }
+                        }
                     }
                 });
             }
@@ -333,6 +367,12 @@ impl Handwriting {
         // Draw the texture
         self.e.canvas_rasterizer.show(ui.ctx(), &painter, mesh_rect);
 
+        if let Some(tool_position) = self.e.tool_position && let Tool::Eraser = self.e.tool {
+            let pos = to_screen * tool_position;
+            let shape = Shape::circle_stroke(pos, tool::eraser::RADIUS, style.stroke);
+            painter.add(shape);
+        }
+
         response
     }
 
@@ -512,34 +552,6 @@ impl Handwriting {
 
         bytes.into_boxed_slice()
     }
-
-    /// Handle a [ToolEvent]. Returns true if a stroke was completed.
-    fn on_tool_event(&mut self, tool_event: ToolEvent) -> bool {
-        match tool_event {
-            ToolEvent::Press { at } => {
-                debug_assert!(self.e.current_stroke.is_empty());
-                self.push_to_stroke(at);
-                false
-            }
-            ToolEvent::Move { to } => {
-                self.push_to_stroke(to);
-                false
-            }
-            ToolEvent::Release => {
-                debug_assert!(!self.e.current_stroke.is_empty());
-                self.strokes.push(mem::take(&mut self.e.current_stroke));
-                true
-            }
-        }
-    }
-}
-
-/// A simple event that can defines how a tool (e.g. the pen) is used on a [Handwriting].
-#[derive(Serialize)]
-enum ToolEvent {
-    Press { at: Pos2 },
-    Move { to: Pos2 },
-    Release,
 }
 
 /// Convert [egui::Event]s to [ToolEvent]s.

src/handwriting/tool/eraser.rs

@@ -0,0 +1,32 @@
+use crate::handwriting::{Handwriting, ToolEvent};
+use egui::Pos2;
+
+pub const RADIUS: f32 = 12.0;
+
+/// Handle a [ToolEvent]. Returns true if a stroke was completed.
+pub fn on_tool_event(handwriting: &mut Handwriting, tool_event: ToolEvent) -> bool {
+    match tool_event {
+        ToolEvent::Press { at } => {
+            erase(handwriting, at, RADIUS)
+        }
+        ToolEvent::Move { to } => {
+            erase(handwriting, to, RADIUS)
+        }
+        ToolEvent::Release => {
+            false            
+        }
+    }
+
+}
+
+fn erase(handwriting: &mut Handwriting, at: Pos2, radius: f32) -> bool {
+    let strokes = handwriting.strokes.len();
+
+    handwriting.strokes.retain(|stroke| {
+        stroke.iter().all(|&point| {
+            (point - at).length() > radius
+        })
+    });
+
+    handwriting.strokes.len() < strokes
+}

src/handwriting/tool/mod.rs

@@ -0,0 +1,28 @@
+pub mod pencil;
+pub mod eraser;
+
+use egui::Pos2;
+use serde::Serialize;
+
+pub enum Tool {
+    Pencil,
+    Eraser,
+}
+
+/// A simple event that can defines how a tool (e.g. the pen) is used on a [Handwriting].
+#[derive(Debug, Serialize, Copy, Clone)]
+pub enum ToolEvent {
+    Press { at: Pos2 },
+    Move { to: Pos2 },
+    Release,
+}
+
+impl ToolEvent {
+    pub const fn position(&self) -> Option<Pos2> {
+        match self {
+            &ToolEvent::Press { at } => Some(at),
+            &ToolEvent::Move { to } => Some(to),
+            ToolEvent::Release => None,
+        }
+    }
+}

src/handwriting/tool/pencil.rs

@@ -0,0 +1,22 @@
+use crate::handwriting::{Handwriting, ToolEvent};
+use std::mem;
+
+/// Handle a [ToolEvent]. Returns true if a stroke was completed.
+pub fn on_tool_event(handwriting: &mut Handwriting, tool_event: ToolEvent) -> bool {
+    match tool_event {
+        ToolEvent::Press { at } => {
+            debug_assert!(handwriting.e.current_stroke.is_empty());
+            handwriting.push_to_stroke(at);
+            false
+        }
+        ToolEvent::Move { to } => {
+            handwriting.push_to_stroke(to);
+            false
+        }
+        ToolEvent::Release => {
+            debug_assert!(!handwriting.e.current_stroke.is_empty());
+            handwriting.strokes.push(mem::take(&mut handwriting.e.current_stroke));
+            true
+        }
+    }
+}