Initial cGridStructGen refactoring.

Ref.: #987.

src/Generating/GridStructGen.h

@@ -0,0 +1,124 @@
+
+// GridStructGen.h
+
+// Declares the cGridStructGen class representing a common base class for structure generators that place structures in a semi-random grid
+
+
+
+
+
+#pragma once
+
+#include "ComposableGenerator.h"
+
+
+
+
+
+/** Generates structures in a semi-random grid.
+Defines a grid in the XZ space with predefined cell size in each direction. Each cell then receives exactly
+one structure (provided by the descendant class). The structure is placed within the cell, but doesn't need
+to be bounded by the cell, it can be well outside the cell; the generator uses the MaxStructureSize parameter
+to determine how far away from the cell the structure can be at most.
+This class provides a cache for the structures generated for successive chunks and manages that cache. It
+also provides the cFinishGen override that uses the cache to actually generate the structure into chunk data.
+
+After generating each chunk the cache is checked for size, each item in the cache has a cost associated with
+it and the cache is trimmed (from its least-recently-used end) so that the sum of the cost in the cache is
+less than m_MaxCacheSize
+
+To use this class, declare a descendant class that implements the overridable methods, then create an
+instance of that class. The descendant must provide the CreateStructure() function that is called to generate
+a structure at the specific grid cell.
+
+The descendant must use a specific cStructure descendant to provide the actual structure that gets generated.
+The structure must provide the DrawIntoChunk() function that generates the structure into the chunk data, and
+can override the GetCacheCost() function that returns the cost of that structure in the cache.
+*/
+class cGridStructGen :
+	public cFinishGen
+{
+public:
+	cGridStructGen(
+		int a_Seed,
+		int a_GridSizeX, int a_GridSizeZ,
+		int a_MaxStructureSizeX, int a_MaxStructureSizeZ,
+		size_t a_MaxCacheSize
+	);
+	
+protected:
+	/** Represents a single structure that occupies the grid point. Knows how to draw itself into a chunk. */
+	class cStructure
+	{
+	public:
+		/** The origin (the coords of the gridpoint for which the structure is generated) */
+		int m_OriginX, m_OriginZ;
+		
+		
+		/** Creates a structure that has its originset at the specified coords. */
+		cStructure (int a_OriginX, int a_OriginZ) :
+			m_OriginX(a_OriginX),
+			m_OriginZ(a_OriginZ)
+		{
+		}
+		
+		// Force a virtual destructor in descendants:
+		virtual ~cStructure() {}
+		
+		/** Draws self into the specified chunk */
+		virtual void DrawIntoChunk(cChunkDesc & a_ChunkDesc) = 0;
+		
+		/** Returns the cost of keeping this structure in the cache */
+		virtual size_t GetCacheCost(void) const { return 1; }
+	} ;
+	typedef SharedPtr<cStructure> cStructurePtr;
+	typedef std::list<cStructurePtr> cStructurePtrs;
+	
+	
+	/** Seed for generating the semi-random grid. */
+	int m_Seed;
+	
+	/** The size of each grid's cell in the X axis */
+	int m_GridSizeX;
+	
+	/** The size of each grid's cell in the Z axis */
+	int m_GridSizeZ;
+	
+	/** Maximum theoretical size of the structure in the X axis.
+	This limits the structures considered for a single chunk, so the lesser the number, the better performance.
+	Structures large than this may get cropped. */
+	int m_MaxStructureSizeX;
+	
+	/** Maximum theoretical size of the structure in the Z axis.
+	This limits the structures considered for a single chunk, so the lesser the number, the better performance.
+	Structures large than this may get cropped. */
+	int m_MaxStructureSizeZ;
+	
+	/** Maximum allowed sum of costs for items in the cache. Items that are over this cost are removed from the
+	cache, oldest-first */
+	size_t m_MaxCacheSize;
+	
+	/** Cache for the most recently generated structures, ordered by the recentness. */
+	cStructurePtrs m_Cache;
+	
+	
+	/** Clears everything from the cache */
+	void ClearCache(void);
+	
+	/** Returns all structures that may intersect the given chunk.
+	The structures are considered as intersecting iff their bounding box (defined by m_MaxStructureSize)
+	around their gridpoint intersects the chunk. */
+	void GetStructuresForChunk(int a_ChunkX, int a_ChunkZ, cStructurePtrs & a_Structures);
+
+	// cFinishGen overrides:
+	virtual void GenFinish(cChunkDesc & a_ChunkDesc) override;
+	
+	// Functions for the descendants to override:
+	/** Create a new structure at the specified gridpoint */
+	virtual cStructurePtr CreateStructure(int a_OriginX, int a_OriginZ) = 0;
+} ;
+
+
+
+
+