Initial stab at pulling the pathing out.

pathing.cpp

@@ -0,0 +1,92 @@
+#include "pathing.hpp"
+#include <vector>
+
+using std::vector;
+
+inline void add_neighbors(PointList &neighbors, Matrix &closed, size_t y, size_t x) {
+  size_t h = closed.size();
+  size_t w = closed[0].size();
+  vector<size_t> rows{y - 1, y, y + 1};
+  vector<size_t> cols{x - 1, x, x + 1};
+
+  for(size_t row : rows) {
+    for(size_t col : cols) {
+      if((0 <= row && row < h) &&
+          (0 <= col && col < w) &&
+          closed[row][col] == 0)
+      {
+        closed[row][col] = 1;
+        neighbors.push_back({.x=col, .y=row});
+      }
+    }
+  }
+}
+
+inline void matrix_assign(Matrix &out, int new_value) {
+  for(auto &row : out) {
+    row.assign(row.size(), new_value);
+  }
+}
+
+void Pathing::compute_paths(Matrix &walls) {
+  INVARIANT();
+  // Initialize the new array with every pixel at limit distance
+  // NOTE: this is normally ones() * limit
+  int limit = $limit == 0 ? $height * $width : $limit;
+  matrix_assign($paths, limit);
+
+  Matrix closed = walls;
+  PointList starting_pixels;
+  PointList open_pixels;
+
+  // First pass: Add starting pixels and put them in closed
+  for(size_t counter = 0; counter < $height * $width; counter++) {
+    size_t x = counter % $width; // BUG: is this right?
+    size_t y = counter / $width;
+    if($input[y][x] == 0) {
+      $paths[y][x] = 0;
+      closed[y][x] = 1;
+      starting_pixels.push_back({.x=x,.y=y});
+    }
+  }
+
+  // Second pass: Add border to open
+  for(auto sp : starting_pixels) {
+    add_neighbors(open_pixels, closed, sp.y, sp.x);
+  }
+
+  // Third pass: Iterate filling in the open list
+  int counter = 1; // leave this here so it's available below
+  for(; counter < limit && !open_pixels.empty(); ++counter) {
+    PointList next_open;
+    for(auto sp : open_pixels) {
+      $paths[sp.y][sp.x] = counter;
+      add_neighbors(next_open, closed, sp.y, sp.x);
+    }
+    open_pixels = next_open;
+  }
+
+  // Last pass: flood last pixels
+  for(auto sp : open_pixels) {
+    $paths[sp.y][sp.x] = counter;
+  }
+}
+
+void Pathing::set_target(const Point &at, int value) {
+  $input[at.y][at.x] = 0;
+}
+
+void Pathing::clear_target(const Point &at) {
+  $input[at.y][at.x] = 1;
+}
+
+bool Pathing::INVARIANT() {
+  using dbc::check;
+
+  check($paths.size() == $height, "paths wrong height");
+  check($paths[0].size() == $width, "paths wrong width");
+  check($input.size() == $height, "input wrong height");
+  check($input[0].size() == $width, "input wrong width");
+
+  return true;
+}