feat: pathfinding for ghosts, add debug rendering of paths

src/entity/ghost.rs

@@ -5,6 +5,7 @@
 //! a traverser and display directional animated textures.
 
 use glam::Vec2;
+use pathfinding::prelude::dijkstra;
 use rand::prelude::*;
 use smallvec::SmallVec;
 
@@ -175,6 +176,40 @@ impl Ghost {
         Vec2::new(pos.x + BOARD_PIXEL_OFFSET.x as f32, pos.y + BOARD_PIXEL_OFFSET.y as f32)
     }
 
+    /// Calculates the shortest path from the ghost's current position to a target node using Dijkstra's algorithm.
+    ///
+    /// Returns a vector of NodeIds representing the path, or None if no path exists.
+    /// The path includes the current node and the target node.
+    pub fn calculate_path_to_target(&self, graph: &Graph, target: NodeId) -> Option<Vec<NodeId>> {
+        let start_node = self.traverser.position.from_node_id();
+
+        // Use Dijkstra's algorithm to find the shortest path
+        let result = dijkstra(
+            &start_node,
+            |&node_id| {
+                // Get all edges from the current node
+                graph.adjacency_list[node_id]
+                    .edges()
+                    .filter(|edge| can_ghost_traverse(*edge))
+                    .map(|edge| (edge.target, (edge.distance * 100.0) as u32))
+                    .collect::<Vec<_>>()
+            },
+            |&node_id| node_id == target,
+        );
+
+        result.map(|(path, _cost)| path)
+    }
+
+    /// Returns the ghost's color for debug rendering.
+    pub fn debug_color(&self) -> sdl2::pixels::Color {
+        match self.ghost_type {
+            GhostType::Blinky => sdl2::pixels::Color::RGB(255, 0, 0),    // Red
+            GhostType::Pinky => sdl2::pixels::Color::RGB(255, 182, 255), // Pink
+            GhostType::Inky => sdl2::pixels::Color::RGB(0, 255, 255),    // Cyan
+            GhostType::Clyde => sdl2::pixels::Color::RGB(255, 182, 85),  // Orange
+        }
+    }
+
     /// Renders the ghost at its current position.
     ///
     /// Draws the appropriate directional sprite based on the ghost's

src/entity/pacman.rs

@@ -111,6 +111,17 @@ impl Pacman {
         }
     }
 
+    /// Returns the current node ID that Pac-Man is at or moving towards.
+    ///
+    /// If Pac-Man is at a node, returns that node ID.
+    /// If Pac-Man is between nodes, returns the node it's moving towards.
+    pub fn current_node_id(&self) -> NodeId {
+        match self.traverser.position {
+            Position::AtNode(node_id) => node_id,
+            Position::BetweenNodes { to, .. } => to,
+        }
+    }
+
     /// Renders Pac-Man to the canvas.
     ///
     /// Calculates screen position, determines if Pac-Man is stopped,

src/game.rs

@@ -173,12 +173,65 @@ impl Game {
         if self.debug_mode {
             self.map
                 .debug_render_with_cursor(canvas, &mut self.text_texture, &mut self.atlas, cursor_pos);
+            self.render_pathfinding_debug(canvas)?;
         }
         self.draw_hud(canvas)?;
         canvas.present();
         Ok(())
     }
 
+    /// Renders pathfinding debug lines from each ghost to Pac-Man.
+    ///
+    /// Each ghost's path is drawn in its respective color with a small offset
+    /// to prevent overlapping lines.
+    fn render_pathfinding_debug<T: RenderTarget>(&self, canvas: &mut Canvas<T>) -> Result<()> {
+        let pacman_node = self.pacman.current_node_id();
+
+        for (i, ghost) in self.ghosts.iter().enumerate() {
+            if let Some(path) = ghost.calculate_path_to_target(&self.map.graph, pacman_node) {
+                if path.len() < 2 {
+                    continue; // Skip if path is too short
+                }
+
+                // Set the ghost's color
+                canvas.set_draw_color(ghost.debug_color());
+
+                // Calculate offset based on ghost index to prevent overlapping lines
+                let offset = (i as f32) * 2.0 - 3.0; // Offset range: -3.0 to 3.0
+
+                // Calculate a consistent offset direction for the entire path
+                let first_node = self.map.graph.get_node(path[0]).unwrap();
+                let last_node = self.map.graph.get_node(path[path.len() - 1]).unwrap();
+                let first_pos = first_node.position + crate::constants::BOARD_PIXEL_OFFSET.as_vec2();
+                let last_pos = last_node.position + crate::constants::BOARD_PIXEL_OFFSET.as_vec2();
+
+                // Use the overall direction from start to end to determine the perpendicular offset
+                let overall_dir = (last_pos - first_pos).normalize();
+                let perp_dir = glam::Vec2::new(-overall_dir.y, overall_dir.x);
+
+                // Calculate offset positions for all nodes using the same perpendicular direction
+                let mut offset_positions = Vec::new();
+                for &node_id in &path {
+                    let node = self.map.graph.get_node(node_id).unwrap();
+                    let pos = node.position + crate::constants::BOARD_PIXEL_OFFSET.as_vec2();
+                    offset_positions.push(pos + perp_dir * offset);
+                }
+
+                // Draw lines between the offset positions
+                for window in offset_positions.windows(2) {
+                    canvas
+                        .draw_line(
+                            (window[0].x as i32, window[0].y as i32),
+                            (window[1].x as i32, window[1].y as i32),
+                        )
+                        .map_err(anyhow::Error::msg)?;
+                }
+            }
+        }
+
+        Ok(())
+    }
+
     fn draw_hud<T: RenderTarget>(&mut self, canvas: &mut Canvas<T>) -> Result<()> {
         let lives = 3;
         let score_text = format!("{:02}", self.score);

tests/pathfinding.rs

@@ -0,0 +1,117 @@
+use pacman::entity::direction::Direction;
+use pacman::entity::ghost::{Ghost, GhostType};
+use pacman::entity::graph::{Graph, Node};
+use pacman::texture::sprite::{AtlasMapper, MapperFrame, SpriteAtlas};
+use std::collections::HashMap;
+
+fn create_test_atlas() -> SpriteAtlas {
+    let mut frames = HashMap::new();
+    let directions = ["up", "down", "left", "right"];
+    let ghost_types = ["blinky", "pinky", "inky", "clyde"];
+
+    for ghost_type in &ghost_types {
+        for (i, dir) in directions.iter().enumerate() {
+            frames.insert(
+                format!("ghost/{}/{}_{}.png", ghost_type, dir, "a"),
+                MapperFrame {
+                    x: i as u16 * 16,
+                    y: 0,
+                    width: 16,
+                    height: 16,
+                },
+            );
+            frames.insert(
+                format!("ghost/{}/{}_{}.png", ghost_type, dir, "b"),
+                MapperFrame {
+                    x: i as u16 * 16,
+                    y: 16,
+                    width: 16,
+                    height: 16,
+                },
+            );
+        }
+    }
+
+    let mapper = AtlasMapper { frames };
+    let dummy_texture = unsafe { std::mem::zeroed() };
+    SpriteAtlas::new(dummy_texture, mapper)
+}
+
+#[test]
+fn test_ghost_pathfinding() {
+    // Create a simple test graph
+    let mut graph = Graph::new();
+
+    // Add nodes in a simple line: 0 -> 1 -> 2
+    let node0 = graph.add_node(Node {
+        position: glam::Vec2::new(0.0, 0.0),
+    });
+    let node1 = graph.add_node(Node {
+        position: glam::Vec2::new(10.0, 0.0),
+    });
+    let node2 = graph.add_node(Node {
+        position: glam::Vec2::new(20.0, 0.0),
+    });
+
+    // Connect the nodes
+    graph.connect(node0, node1, false, None, Direction::Right).unwrap();
+    graph.connect(node1, node2, false, None, Direction::Right).unwrap();
+
+    // Create a test atlas for the ghost
+    let atlas = create_test_atlas();
+
+    // Create a ghost at node 0
+    let ghost = Ghost::new(&graph, node0, GhostType::Blinky, &atlas);
+
+    // Test pathfinding from node 0 to node 2
+    let path = ghost.calculate_path_to_target(&graph, node2);
+
+    assert!(path.is_some());
+    let path = path.unwrap();
+    assert_eq!(path, vec![node0, node1, node2]);
+}
+
+#[test]
+fn test_ghost_pathfinding_no_path() {
+    // Create a test graph with disconnected components
+    let mut graph = Graph::new();
+
+    let node0 = graph.add_node(Node {
+        position: glam::Vec2::new(0.0, 0.0),
+    });
+    let node1 = graph.add_node(Node {
+        position: glam::Vec2::new(10.0, 0.0),
+    });
+
+    // Don't connect the nodes
+    let atlas = create_test_atlas();
+    let ghost = Ghost::new(&graph, node0, GhostType::Blinky, &atlas);
+
+    // Test pathfinding when no path exists
+    let path = ghost.calculate_path_to_target(&graph, node1);
+
+    assert!(path.is_none());
+}
+
+#[test]
+fn test_ghost_debug_colors() {
+    let atlas = create_test_atlas();
+    let mut graph = Graph::new();
+    let node = graph.add_node(Node {
+        position: glam::Vec2::new(0.0, 0.0),
+    });
+
+    let blinky = Ghost::new(&graph, node, GhostType::Blinky, &atlas);
+    let pinky = Ghost::new(&graph, node, GhostType::Pinky, &atlas);
+    let inky = Ghost::new(&graph, node, GhostType::Inky, &atlas);
+    let clyde = Ghost::new(&graph, node, GhostType::Clyde, &atlas);
+
+    // Test that each ghost has a different debug color
+    let colors = std::collections::HashSet::from([
+        blinky.debug_color(),
+        pinky.debug_color(),
+        inky.debug_color(),
+        clyde.debug_color(),
+    ]);
+    assert_eq!(colors.len(), 4, "All ghost colors should be unique");
+}