diff --git a/Makefile b/Makefile
index 736e35d..adb9559 100644
--- a/Makefile
+++ b/Makefile
@@ -26,8 +26,11 @@ run: build test
 clean:
 	meson compile --clean -C builddir
 
-debug:
-	gdb --nx -x .gdbinit builddir/roguish.exe
+debug_test: build
+	gdb --nx -x .gdbinit --ex run --args builddir/runtests.exe
+
+debug_run: build
+	gdb --nx -x .gdbinit --batch --ex run --ex bt --ex q --args builddir/roguish.exe
 
 cover:
 	gcovr --html coverage/index.html  --gcov-ignore-errors=no_working_dir_found --exclude "scratchpad.*" --exclude "subprojects.*" --html-nested coverage/
diff --git a/map.cpp b/map.cpp
index 4357f09..2f941ea 100644
--- a/map.cpp
+++ b/map.cpp
@@ -64,26 +64,36 @@ Map::Map(Matrix input_map, Matrix walls_map, int limit) :
 {
   $width = $walls[0].size();
   $height = $walls.size();
+  $paths = Matrix($height, MatrixRow($width, 1));
+  $lightmap = Matrix($height, MatrixRow($width, 0));
 }
 
-void Map::make_paths() {
-  size_t h = $input_map.size();
-  size_t w = $input_map[0].size();
+inline void matrix_assign(Matrix &out, int new_value) {
+  for(auto &row : out) {
+    row.assign(row.size(), new_value);
+  }
+}
 
+/*
+ * Used https://github.com/HenrYxZ/dijkstra-map as a reference.
+ */
+void Map::make_paths() {
+  INVARIANT();
   // Initialize the new array with every pixel at limit distance
   // NOTE: this is normally ones() * limit
-  int limit = $limit == 0 ? h * w : $limit;
-  Matrix new_arr = Matrix(h, MatrixRow(w, 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 < h * w; counter++) {
-    size_t x = counter % w;
-    size_t y = counter / w;
+ 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_map[y][x] == 0) {
-      new_arr[y][x] = 0;
+      $paths[y][x] = 0;
       closed[y][x] = 1;
       starting_pixels.push_back({.x=x,.y=y});
     }
@@ -99,7 +109,7 @@ void Map::make_paths() {
   for(; counter < limit && !open_pixels.empty(); ++counter) {
     PointList next_open;
     for(auto sp : open_pixels) {
-      new_arr[sp.y][sp.x] = counter;
+      $paths[sp.y][sp.x] = counter;
       add_neighbors(next_open, closed, sp.y, sp.x);
     }
     open_pixels = next_open;
@@ -107,22 +117,17 @@ void Map::make_paths() {
 
   // Last pass: flood last pixels
   for(auto sp : open_pixels) {
-    new_arr[sp.y][sp.x] = counter;
+    $paths[sp.y][sp.x] = counter;
   }
-
-  $paths = new_arr;
 }
 
 void Map::make_room(size_t origin_x, size_t origin_y, size_t w, size_t h) {
-  dbc::pre("x out of bounds", origin_x < $width);
-  dbc::pre("y out of bounds", origin_y < $height);
-  dbc::pre("w out of bounds", w <= $width);
-  dbc::pre("h out of bounds", h <= $height);
+  INVARIANT();
+  dbc::pre("y out of bounds", origin_y + h < $height);
+  dbc::pre("x out of bounds", origin_x + w < $width);
 
   for(size_t y = origin_y; y < origin_y + h; ++y) {
-    dbc::check(y < $walls.size(), "y is out of bounds");
     for(size_t x = origin_x; x < origin_x + w; ++x) {
-      dbc::check(x < $walls[y].size(), "x is out of bounds");
       $walls[y][x] = INV_SPACE;
     }
   }
@@ -375,11 +380,7 @@ Point Map::center_camera(const Point &around, size_t view_x, size_t view_y) {
 }
 
 void Map::reset_light() {
-  for(auto &row : $lightmap) {
-    for(size_t i = 0; i < row.size(); i++) {
-      row[i] = lighting::MIN;
-    }
-  }
+  matrix_assign($lightmap, lighting::MIN);
 }
 
 void Map::clear_light_target(const Point &at) {
@@ -390,7 +391,6 @@ void Map::set_light_target(const Point &at, int value) {
   set_target(at, value);
 }
 
-
 void Map::path_light() {
     make_paths();
 }
@@ -417,10 +417,13 @@ void Map::render_light(LightSource source, Point at) {
   clear_light_target(at);
   vector<Point> has_light;
 
-  for(size_t x = min.x; x <= max.x; ++x) {
-    for(size_t y = min.y; y <= max.y; ++y) {
-      if($paths[y][x] != UNPATH) {
-        $lightmap[y][x] = light_level(source.strength, x, y);
+  for(size_t y = min.y; y <= max.y; ++y) {
+    auto &light_row = $lightmap[y];
+    auto &path_row = $paths[y];
+
+    for(size_t x = min.x; x <= max.x; ++x) {
+      if(path_row[x] != UNPATH) {
+        light_row[x] = light_level(source.strength, x, y);
         has_light.push_back({x,y});
       }
     }
@@ -428,14 +431,30 @@ void Map::render_light(LightSource source, Point at) {
 
   const int wall_light = source.strength + WALL_LIGHT_LEVEL;
   for(auto point : has_light) {
-    for(int i = -1; i <= 1; i++) {
-      for(int j = -1; j <= 1; j++) {
-        if(!inmap(point.x+i, point.y+j)) continue;
+    for(int j = -1;point.y+j >= 0 && j <= 1 && point.y+j < $height; j++) {
+      auto &path_row = $paths[point.y+j];
+      auto &light_row = $lightmap[point.y+j];
 
-        if($paths[point.y+j][point.x+i] == UNPATH) {
-          $lightmap[point.y+j][point.x+i] = light_level(wall_light, point.x, point.y);
+      for(int i = -1; point.x+i >= 0 && i <= 1 && point.x+i < $width; i++) {
+        if(path_row[point.x+i] == UNPATH) {
+          light_row[point.x+i] = light_level(wall_light, point.x, point.y);
         }
       }
     }
   }
 }
+
+bool Map::INVARIANT() {
+  using dbc::check;
+
+  check($paths.size() == height(), "paths wrong height");
+  check($paths[0].size() == width(), "paths wrong width");
+  check($input_map.size() == height(), "input_map wrong height");
+  check($input_map[0].size() == width(), "input_map wrong width");
+  check($walls.size() == height(), "walls wrong height");
+  check($walls[0].size() == width(), "walls wrong width");
+  check($lightmap.size() == height(), "lightmap wrong height");
+  check($lightmap[0].size() == width(), "lightmap wrong width");
+
+  return true;
+}
diff --git a/map.hpp b/map.hpp
index 378efb9..f3d4085 100644
--- a/map.hpp
+++ b/map.hpp
@@ -92,4 +92,5 @@ public:
   void render_light(LightSource source, Point at);
 
   void dump();
+  bool INVARIANT();
 };
diff --git a/meson.build b/meson.build
index 0b52c9b..a08d553 100644
--- a/meson.build
+++ b/meson.build
@@ -35,13 +35,13 @@ runtests = executable('runtests', [
   'tests/map.cpp',
   'tests/collider.cpp',
   'tests/components.cpp',
-  'tests/sound.cpp',
   'tests/dinkyecs.cpp',
   'tests/ansi_parser.cpp',
   'tests/config.cpp',
   'tests/save.cpp',
   'tests/render.cpp',
   'tests/panel.cpp',
+  'tests/sound.cpp',
   ],
   dependencies: dependencies)
 
diff --git a/tests/map.cpp b/tests/map.cpp
index 35327f9..c17b209 100644
--- a/tests/map.cpp
+++ b/tests/map.cpp
@@ -22,6 +22,8 @@ TEST_CASE("dijkstra algo test", "[map]") {
         test["walls"],
         test["limit"]);
 
+    REQUIRE(map.INVARIANT());
+
     map.make_paths();
     Matrix &paths = map.paths();
 
@@ -31,6 +33,7 @@ TEST_CASE("dijkstra algo test", "[map]") {
       dump_map("RESULT", paths);
     }
 
+    REQUIRE(map.INVARIANT());
     REQUIRE(paths == expected);
   }
 }