From c09a4f39f742a94b150cad6a3fb0bbbfbb99e495 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Fri, 24 Mar 2017 22:47:19 +0100
Subject: Switch to toroidial world matrix

i.e. glue together top and bottom respectively right hand side and left hand side borders.

This makes for nicer life behaviour in constrained worlds.
---
 life.cc                |  2 +-
 src/util/torus_array.h | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
 src/world.h            | 35 ++++++++++++++++-----------------
 3 files changed, 69 insertions(+), 20 deletions(-)
 create mode 100644 src/util/torus_array.h

diff --git a/life.cc b/life.cc
index 3af4e69..a60667e 100644
--- a/life.cc
+++ b/life.cc
@@ -41,7 +41,7 @@ void draw(
 
 int main(int, char*[]) {
 	util::TermGuard    guard;
-	life::World<60,40> world;
+	life::World<80,40> world;
 
 	std::size_t worldOffsetX = tb_width()  / 2 - world.width  / 2;
 	std::size_t worldOffsetY = tb_height() / 2 - world.height / 2;
diff --git a/src/util/torus_array.h b/src/util/torus_array.h
new file mode 100644
index 0000000..bef0c9f
--- /dev/null
+++ b/src/util/torus_array.h
@@ -0,0 +1,52 @@
+#ifndef LIFE_SRC_UTIL_TORUS_ARRAY_
+#define LIFE_SRC_UTIL_TORUS_ARRAY_
+
+#include <array>
+#include <cstdint>
+
+namespace life {
+namespace util {
+
+template<
+	typename    TYPE,
+	std::size_t WIDTH,
+	std::size_t HEIGHT
+>
+class TorusArray {
+	static std::size_t toMatrixColumn(const std::ptrdiff_t x) {
+		if ( x >= 0 ) {
+			return x % WIDTH;
+		} else {
+			return WIDTH - ( std::abs(x) % WIDTH );
+		}
+	}
+
+	static std::size_t toMatrixRow(const std::ptrdiff_t y) {
+		if ( y >= 0 ) {
+			return y % HEIGHT;
+		} else {
+			return HEIGHT - ( std::abs(y) % HEIGHT );
+		}
+	}
+
+	public:
+		static const std::size_t width  = WIDTH;
+		static const std::size_t height = HEIGHT;
+
+		TYPE get(const std::ptrdiff_t x, const std::ptrdiff_t y) const {
+			return this->matrix_[toMatrixRow(y)][toMatrixColumn(x)];
+		}
+
+		void set(const std::ptrdiff_t x, const std::ptrdiff_t y, TYPE&& value) {
+			this->matrix_[toMatrixRow(y)][toMatrixColumn(x)] = value;
+		}
+	
+	private:
+		std::array<std::array<TYPE, WIDTH>, HEIGHT> matrix_;
+
+};
+
+}
+}
+
+#endif  // LIFE_SRC_UTIL_TORUS_ARRAY_
diff --git a/src/world.h b/src/world.h
index e70e20e..a09eb5a 100644
--- a/src/world.h
+++ b/src/world.h
@@ -1,12 +1,12 @@
 #ifndef LIFE_SRC_WORLD_H_
 #define LIFE_SRC_WORLD_H_
 
-#include <array>
 #include <stack>
 #include <tuple>
 #include <cstdint>
 
 #include "util/box_traverser.h"
+#include "util/torus_array.h"
 
 namespace life {
 
@@ -22,19 +22,16 @@ class World {
 		World():
 			area_(width, height) {
 			this->area_.for_each([&](std::size_t i, std::size_t j) {
-				this->matrix_[j][i] = false;
+				this->matrix_.set(i, j, false);
 			});
 		}
 
-		bool isLifeAt(std::ptrdiff_t x, std::ptrdiff_t y) const {
-			if ( this->area_(x, y) ) {
-				return this->matrix_[y][x];
-			} else {
-				return false; // end of world is dead
-			}
+		bool isLifeAt(const std::ptrdiff_t x, const std::ptrdiff_t y) const {
+			return this->matrix_.get(x, y);
 		}
 
-		std::uint8_t lifeDensityAt(std::size_t x, std::size_t y) const {
+		std::uint8_t lifeDensityAt(
+			const std::ptrdiff_t x, const std::ptrdiff_t y) const {
 			std::uint8_t counter{};
 
 			counter += this->isLifeAt(x - 1, y);
@@ -57,20 +54,20 @@ class World {
 			return this->population_;
 		}
 
-		void summonLifeAt(std::size_t x, std::size_t y) {
+		void summonLifeAt(const std::ptrdiff_t x, const std::ptrdiff_t y) {
 			if ( this->area_(x, y) ) {
-				if ( !this->matrix_[y][x] ) {
-					this->matrix_[y][x] = true;
-					this->population_  += 1;
+				if ( !this->matrix_.get(x, y) ) {
+					this->matrix_.set(x, y, true);
+					this->population_ += 1;
 				}
 			}
 		}
 
-		void extinguishLifeAt(std::size_t x, std::size_t y) {
+		void extinguishLifeAt(const std::ptrdiff_t x, const std::ptrdiff_t y) {
 			if ( this->area_(x, y) ) {
-				if ( this->matrix_[y][x] ) {
-					this->matrix_[y][x] = false;
-					this->population_  -= 1;
+				if ( this->matrix_.get(x, y) ) {
+					this->matrix_.set(x, y, false);
+					this->population_ -= 1;
 				}
 			}
 		}
@@ -83,7 +80,7 @@ class World {
 			this->area_.for_each([&](std::size_t i, std::size_t j) {
 				const std::uint8_t d{this->lifeDensityAt(i, j)};
 
-				if ( this->matrix_[j][i] ) {
+				if ( this->matrix_.get(i, j) ) {
 					if ( d < 2 ) {
 						updates.emplace(i, j, false);
 					} else if ( d == 2 || d == 3 ) {
@@ -122,7 +119,7 @@ class World {
 
 		std::size_t age_{};
 		std::size_t population_{};
-		std::array<std::array<bool, WIDTH>, HEIGHT> matrix_;
+		util::TorusArray<bool, WIDTH, HEIGHT> matrix_;
 
 };
 
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