摄像机系统，和子对象绑定

include/mesh.hpp

@@ -44,6 +44,33 @@ class Mesh {
         return mesh;
     }
 
+    static Mesh grid(int half_cells = 12) {
+        Mesh mesh;
+        const float world_to_local = 1.0F / 0.35F;
+        const float half_extent = static_cast<float>(half_cells) * world_to_local;
+        const float line_half_width = 0.012F * world_to_local;
+        const std::array<float, 4> line_color{1.0F, 1.0F, 1.0F, 1.0F};
+        auto add_rect = [&](float left, float bottom, float right, float top) {
+            const uint32_t base = static_cast<uint32_t>(mesh.vertices.size());
+            mesh.vertices.insert(mesh.vertices.end(), {
+                {{left, bottom}, line_color, {0.0F, 0.0F}},
+                {{right, bottom}, line_color, {1.0F, 0.0F}},
+                {{right, top}, line_color, {1.0F, 1.0F}},
+                {{left, top}, line_color, {0.0F, 1.0F}},
+            });
+            mesh.indices.insert(mesh.indices.end(),
+                                {base, base + 1, base + 2, base + 2, base + 3, base});
+        };
+        for (int cell = -half_cells; cell <= half_cells; ++cell) {
+            const float coordinate = static_cast<float>(cell) * world_to_local;
+            add_rect(coordinate - line_half_width, -half_extent, coordinate + line_half_width,
+                     half_extent);
+            add_rect(-half_extent, coordinate - line_half_width, half_extent,
+                     coordinate + line_half_width);
+        }
+        return mesh;
+    }
+
    private:
     std::unique_ptr<std::mutex> color_mutex_ = std::make_unique<std::mutex>();
     std::array<float, 4> color_{1.0F, 1.0F, 1.0F, 1.0F};