diff --git a/include/dynamic_grid.hpp b/include/dynamic_grid.hpp
new file mode 100644
index 0000000..a7a3260
--- /dev/null
+++ b/include/dynamic_grid.hpp
@@ -0,0 +1,163 @@
+#pragma once
+
+#include "field.hpp"
+
+#include <cassert>
+#include <utility>
+#include <array>
+#include <vector>
+#include <algorithm>
+#include <iosfwd>
+#include <functional>
+
+// Position {0,0} is bottom left.
+// Position {W-1, H-1} is top right.
+template <typename T>
+struct DynamicField{
+	using Position = std::pair<int, int>;
+
+	template <typename Input>
+	DynamicField(int W, int H, Input it)
+	: W(W)
+	, H(H)
+	, grid(W*H, 0)
+	{
+		std::copy_n(it, W*H, std::begin(grid));
+	}
+
+	//! \brief Returns true if p represents a valid position
+	auto valid(Position const & p) const {
+		return p.first >= 0 && p.second >= 0
+		    && p.first <  W && p.second < H;
+	}
+
+	//! \brief Returns true if p represents an empty cell
+	auto empty(Position const & p) const {
+		assert(valid(p));
+		return get(p) == 0;
+	}
+
+	//! \brief Returns all neighbors of p
+	//! Only returns valid neighbors (and p does not need to be valid)
+	auto neighbors(Position const & p) const {
+		small_vector<Position, 4> ret;
+
+		static Position nbs[] = {
+			{-1, 0}, {1, 0}, {0, 1}, {0, -1}
+		};
+
+		for(auto&& n : nbs){
+			auto q = Position{p.first + n.first, p.second + n.second};
+			if(valid(q)){
+				ret.push_back(q);
+			}
+		}
+
+		return ret;
+	}
+
+	//! \brief Let the block fall (all the way)
+	auto collapse(){
+		while(vcollapse());
+		while(hcollapse());
+	}
+
+	//! \brief Returns an array of all valid positions
+	auto const & all_positions() const {
+		static auto v = all_positions_impl(W, H);
+		return v;
+	}
+
+	//! \brief Get (mutable) value at p
+	T& get(Position const & p){
+		assert(valid(p));
+		return grid[static_cast<size_t>(p.first + p.second*W)];
+	}
+
+	//! \brief Get value at p
+	T const& get(Position const & p) const {
+		assert(valid(p));
+		return grid[static_cast<size_t>(p.first + p.second*W)];
+	}
+
+	//! \brief Pretty prints grid to out
+	void print(std::ostream& out) const {
+		for(auto y = H; y; --y){
+			for(auto x = 0; x < W; ++x){
+				out << get({x, y-1}) << (x == W-1 ? '\n' : ' ');
+			}
+		}
+	}
+
+private:
+	int W;
+	int H;
+	std::vector<T> grid;
+
+	//! \brief Helper function for all_positions()
+	static auto all_positions_impl(int W, int H) {
+		std::vector<Position> r;
+		for(int y = 0; y < H; ++y)
+			for(int x = 0; x < W; ++x)
+				r.emplace_back(x, y);
+		return r;
+	}
+
+	//! \brief Single vertical collapsing step
+	auto vcollapse(){
+		using namespace std;
+		bool some_change = false;
+		for(auto&& p : all_positions()){
+			if(empty(p)) continue;
+
+			auto q = p;
+			q.second--;
+			if(!valid(q)) continue;
+			if(!empty(q)) continue;
+
+			swap(get(p), get(q));
+			some_change = true;
+		}
+
+		return some_change;
+	}
+
+	//! \brief Single horizontal collapsing step
+	auto hcollapse(){
+		using namespace std;
+		bool some_change = false;
+		for(auto x = 0; x < W-1; ++x){
+			if(!empty_column(x)) continue;
+
+			auto x2 = x+1;
+			for(; x2 < W; ++x2){
+				if(!empty_column(x2)) break;
+			}
+			if(x2 == W) return some_change;
+
+			for(auto y = 0; y < H; ++y){
+				swap(get({x, y}), get({x2, y}));
+			}
+			some_change = true;
+		}
+		return some_change;
+	}
+
+	//! \brief Returns true if the whole column at x is empty
+	auto empty_column(int x){
+		for(auto y = 0; y < H; ++y){
+			if(!empty({x, y})){
+				return false;
+			}
+		}
+		return true;
+	}
+};
+
+template <typename URNG>
+auto random_dynamic_grid(int W, int H, URNG&& r){
+	std::uniform_int_distribution<int> dis(1, 2);
+	std::vector<int> v(W*H);
+	std::generate_n(std::begin(v), W*H, [&]{ return dis(r); });
+	return DynamicField<int>(W, H, std::begin(v));
+}
diff --git a/main.cpp b/main.cpp
index ab16448..5ab3ae4 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,5 +1,5 @@
 
-#include "field.hpp"
+#include "dynamic_grid.hpp"
 #include "clusters.hpp"
 #include "solver.hpp"
 #include "generator.hpp"
@@ -16,7 +16,7 @@ int main(){
 	std::mt19937 gen(rd());
 
 	std::cout << std::endl;
-	auto field = random_field<3, 3>(gen);
+	auto field = random_dynamic_grid(3, 3, gen);
 
 	field.print(std::cout);