From 8c1629af42a10ff7e23bb40100a259bf334a9c60 Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Mon, 2 Feb 2015 01:41:17 +0100
Subject: Change region reader to a visitor pattern

Not keeping the whole region in memory reduces the needed space
to less than 5MB (from about 140).
---
 src/MinedMap.cpp     | 33 +++++++++++++++------------------
 src/World/Region.cpp | 13 +++++++++----
 src/World/Region.hpp | 16 ++++++----------
 3 files changed, 30 insertions(+), 32 deletions(-)

diff --git a/src/MinedMap.cpp b/src/MinedMap.cpp
index f9f9736..3af634d 100644
--- a/src/MinedMap.cpp
+++ b/src/MinedMap.cpp
@@ -40,7 +40,19 @@
 using namespace MinedMap;
 
 
-static void writePNG(const char *filename, const uint32_t data[World::Region::SIZE*World::Chunk::SIZE][World::Region::SIZE*World::Chunk::SIZE]) {
+static const size_t DIM = World::Region::SIZE*World::Chunk::SIZE;
+
+
+static void addChunk(uint32_t image[DIM][DIM], size_t X, size_t Z, const World::Chunk *chunk) {
+	World::Chunk::Blocks layer = chunk->getTopLayer();
+
+	for (size_t x = 0; x < World::Chunk::SIZE; x++) {
+		for (size_t z = 0; z < World::Chunk::SIZE; z++)
+			image[Z*World::Chunk::SIZE+z][X*World::Chunk::SIZE+x] = htonl(layer.blocks[x][z].getColor());
+	}
+}
+
+static void writePNG(const char *filename, const uint32_t data[DIM][DIM]) {
 	std::FILE *f = std::fopen(filename, "wb");
 	if (!f)
 		throw std::system_error(errno, std::generic_category(), "unable to open output file");
@@ -82,24 +94,9 @@ int main(int argc, char *argv[]) {
 		return 1;
 	}
 
-	World::Region region(argv[1]);
-
-	uint32_t image[World::Region::SIZE*World::Chunk::SIZE][World::Region::SIZE*World::Chunk::SIZE] = {};
-
-	for (size_t X = 0; X < World::Region::SIZE; X++) {
-		for (size_t Z = 0; Z < World::Region::SIZE; Z++) {
-			const World::Chunk *chunk = region(X, Z);
-			if (!chunk)
-				continue;
+	uint32_t image[DIM][DIM] = {};
 
-			World::Chunk::Blocks layer = chunk->getTopLayer();
-
-			for (size_t x = 0; x < World::Chunk::SIZE; x++) {
-				for (size_t z = 0; z < World::Chunk::SIZE; z++)
-					image[Z*World::Chunk::SIZE+z][X*World::Chunk::SIZE+x] = htonl(layer.blocks[x][z].getColor());
-			}
-		}
-	}
+	World::Region::visitChunks(argv[1], [&image] (size_t X, size_t Z, const World::Chunk *chunk) { addChunk(image, X, Z, chunk); });
 
 	writePNG(argv[2], image);
 
diff --git a/src/World/Region.cpp b/src/World/Region.cpp
index fec732c..4551d73 100644
--- a/src/World/Region.cpp
+++ b/src/World/Region.cpp
@@ -54,7 +54,7 @@ Region::ChunkMap Region::processHeader(const uint8_t header[4096]) {
 	return map;
 }
 
-Region::Region(const char *filename) {
+void Region::visitChunks(const char *filename, ChunkVisitor visitor) {
 	std::ifstream file;
 	file.exceptions(std::ios::failbit | std::ios::badbit);
 	file.open(filename, std::ios::in | std::ios::binary);
@@ -68,6 +68,8 @@ Region::Region(const char *filename) {
 		chunkMap = processHeader(header);
 	}
 
+	bool seen[SIZE][SIZE] = {};
+
 	size_t i = 1, c = 0;
 	while (!file.eof()) {
 		auto it = chunkMap.find(i);
@@ -80,16 +82,19 @@ Region::Region(const char *filename) {
 		size_t x, z, len;
 		std::tie(x, z, len) = it->second;
 
-		if (chunks[x][z])
+		if (seen[x][z])
 			throw std::invalid_argument("duplicate chunk");
 
+		seen[x][z] = true;
+		c++;
+
 		uint8_t buffer[len * 4096];
 		file.read((char *)buffer, len * 4096);
 
-		chunks[x][z].reset(new Chunk(Buffer(buffer, len * 4096)));
+		Chunk chunk(Buffer(buffer, len * 4096));
+		visitor(x, z, &chunk);
 
 		i += len;
-		c++;
 	}
 
 	if (c != chunkMap.size())
diff --git a/src/World/Region.hpp b/src/World/Region.hpp
index 0843724..d88dbe1 100644
--- a/src/World/Region.hpp
+++ b/src/World/Region.hpp
@@ -28,6 +28,7 @@
 
 #include "Chunk.hpp"
 
+#include <functional>
 #include <memory>
 #include <stdexcept>
 #include <tuple>
@@ -41,23 +42,18 @@ class Region {
 public:
 	static const size_t SIZE = 32;
 
+	typedef std::function<void (size_t, size_t, const Chunk *)> ChunkVisitor;
+
+	Region() = delete;
+
 private:
 	typedef std::tuple<size_t, size_t, size_t> ChunkDesc;
 	typedef std::unordered_map<size_t, ChunkDesc> ChunkMap;
 
-	std::unique_ptr<Chunk> chunks[SIZE][SIZE];
-
 	static ChunkMap processHeader(const uint8_t header[4096]);
 
 public:
-	Region(const char *filename);
-
-	const Chunk * operator()(size_t x, size_t z) {
-		if (x >= SIZE || z >= SIZE)
-			throw std::range_error("Region(): bad coordinates");
-
-		return chunks[x][z].get();
-	}
+	static void visitChunks(const char *filename, ChunkVisitor visitor);
 };
 
 }
-- 
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