RecastDemo: add Load & Save buttons for SoloMesh Sample, and fix warnings (#258)

* Implement saveAll loadAll for Sample_SoloMesh

 - Solo mesh sample is loaded and saved as a tiled mesh containing
   an unique tile, so as to remain compatible with tiled mesh
 - navmesh is saved to/loaded from `solo_navmesh.bin` binary file
 - add and connect the corresponding 'Save/Load' GUI elements

* Fix `implit-fallthrough` gcc warnings

On linux with gcc 7.2.0+ and all warnings treated as errors,
implicit fallthroughs in case statements are considered as errors.
If the comment just below the next `case` or `default` matches
various strings, one of which is `falls through` the fallthrough
is then considered explicit.

RecastDemo/Source/Sample.cpp

@@ -322,3 +322,128 @@ void Sample::renderOverlayToolStates(double* proj, double* model, int* view)
 	}
 }
 
+static const int NAVMESHSET_MAGIC = 'M'<<24 | 'S'<<16 | 'E'<<8 | 'T'; //'MSET';
+static const int NAVMESHSET_VERSION = 1;
+
+struct NavMeshSetHeader
+{
+	int magic;
+	int version;
+	int numTiles;
+	dtNavMeshParams params;
+};
+
+struct NavMeshTileHeader
+{
+	dtTileRef tileRef;
+	int dataSize;
+};
+
+dtNavMesh* Sample::loadAll(const char* path)
+{
+	FILE* fp = fopen(path, "rb");
+	if (!fp) return 0;
+
+	// Read header.
+	NavMeshSetHeader header;
+	size_t readLen = fread(&header, sizeof(NavMeshSetHeader), 1, fp);
+	if (readLen != 1)
+	{
+		fclose(fp);
+		return 0;
+	}
+	if (header.magic != NAVMESHSET_MAGIC)
+	{
+		fclose(fp);
+		return 0;
+	}
+	if (header.version != NAVMESHSET_VERSION)
+	{
+		fclose(fp);
+		return 0;
+	}
+
+	dtNavMesh* mesh = dtAllocNavMesh();
+	if (!mesh)
+	{
+		fclose(fp);
+		return 0;
+	}
+	dtStatus status = mesh->init(&header.params);
+	if (dtStatusFailed(status))
+	{
+		fclose(fp);
+		return 0;
+	}
+
+	// Read tiles.
+	for (int i = 0; i < header.numTiles; ++i)
+	{
+		NavMeshTileHeader tileHeader;
+		readLen = fread(&tileHeader, sizeof(tileHeader), 1, fp);
+		if (readLen != 1)
+		{
+			fclose(fp);
+			return 0;
+		}
+
+		if (!tileHeader.tileRef || !tileHeader.dataSize)
+			break;
+
+		unsigned char* data = (unsigned char*)dtAlloc(tileHeader.dataSize, DT_ALLOC_PERM);
+		if (!data) break;
+		memset(data, 0, tileHeader.dataSize);
+		readLen = fread(data, tileHeader.dataSize, 1, fp);
+		if (readLen != 1)
+		{
+			dtFree(data);
+			fclose(fp);
+			return 0;
+		}
+
+		mesh->addTile(data, tileHeader.dataSize, DT_TILE_FREE_DATA, tileHeader.tileRef, 0);
+	}
+
+	fclose(fp);
+
+	return mesh;
+}
+
+void Sample::saveAll(const char* path, const dtNavMesh* mesh)
+{
+	if (!mesh) return;
+
+	FILE* fp = fopen(path, "wb");
+	if (!fp)
+		return;
+
+	// Store header.
+	NavMeshSetHeader header;
+	header.magic = NAVMESHSET_MAGIC;
+	header.version = NAVMESHSET_VERSION;
+	header.numTiles = 0;
+	for (int i = 0; i < mesh->getMaxTiles(); ++i)
+	{
+		const dtMeshTile* tile = mesh->getTile(i);
+		if (!tile || !tile->header || !tile->dataSize) continue;
+		header.numTiles++;
+	}
+	memcpy(&header.params, mesh->getParams(), sizeof(dtNavMeshParams));
+	fwrite(&header, sizeof(NavMeshSetHeader), 1, fp);
+
+	// Store tiles.
+	for (int i = 0; i < mesh->getMaxTiles(); ++i)
+	{
+		const dtMeshTile* tile = mesh->getTile(i);
+		if (!tile || !tile->header || !tile->dataSize) continue;
+
+		NavMeshTileHeader tileHeader;
+		tileHeader.tileRef = mesh->getTileRef(tile);
+		tileHeader.dataSize = tile->dataSize;
+		fwrite(&tileHeader, sizeof(tileHeader), 1, fp);
+
+		fwrite(tile->data, tile->dataSize, 1, fp);
+	}
+
+	fclose(fp);
+}