BansheeEngine/CamelotRenderer/Include/CmHardwareBuffer.h

/*
-----------------------------------------------------------------------------
This source file is part of OGRE
    (Object-oriented Graphics Rendering Engine)
For the latest info, see http://www.ogre3d.org/

Copyright (c) 2000-2011 Torus Knot Software Ltd

Permission is hereby granted, free of charge, to any person obtaining a copy
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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THE SOFTWARE.
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*/
#ifndef __HardwareBuffer__
#define __HardwareBuffer__

// Precompiler options
#include "CmPrerequisites.h"

namespace CamelotEngine {

	/** \addtogroup Core
	*  @{
	*/
	/** \addtogroup RenderSystem
	*  @{
	*/
	/** Abstract class defining common features of hardware buffers.
    @remarks
 	    A 'hardware buffer' is any area of memory held outside of core system ram,
	    and in our case refers mostly to video ram, although in theory this class
	    could be used with other memory areas such as sound card memory, custom
	    coprocessor memory etc.
    @par
 	    This reflects the fact that memory held outside of main system RAM must 
	    be interacted with in a more formal fashion in order to promote
	    cooperative and optimal usage of the buffers between the various 
	    processing units which manipulate them.
    @par
 	    This abstract class defines the core interface which is common to all
	    buffers, whether it be vertex buffers, index buffers, texture memory
	    or framebuffer memory etc.
	@par
		Buffers have the ability to be 'shadowed' in system memory, this is because
		the kinds of access allowed on hardware buffers is not always as flexible as
		that allowed for areas of system memory - for example it is often either 
		impossible, or extremely undesirable from a performance standpoint to read from
		a hardware buffer; when writing to hardware buffers, you should also write every
		byte and do it sequentially. In situations where this is too restrictive, 
		it is possible to create a hardware, write-only buffer (the most efficient kind) 
		and to back it with a system memory 'shadow' copy which can be read and updated arbitrarily.
		Ogre handles synchronising this buffer with the real hardware buffer (which should still be
		created with the HBU_DYNAMIC flag if you intend to update it very frequently). Whilst this
		approach does have it's own costs, such as increased memory overhead, these costs can 
		often be outweighed by the performance benefits of using a more hardware efficient buffer.
		You should look for the 'useShadowBuffer' parameter on the creation methods used to create
		the buffer of the type you require (see HardwareBufferManager) to enable this feature.
    */
	class CM_EXPORT HardwareBuffer
    {

	    public:
		    /// Enums describing buffer usage; not mutually exclusive
		    enum Usage 
		    {
                /** Static buffer which the application rarely modifies once created. Modifying 
                the contents of this buffer will involve a performance hit.
                */
                HBU_STATIC = 1,
			    /** Indicates the application would like to modify this buffer with the CPU
			    fairly often. 
			    Buffers created with this flag will typically end up in AGP memory rather 
			    than video memory.
			    */
			    HBU_DYNAMIC = 2,
			    /** Indicates the application will never read the contents of the buffer back, 
			    it will only ever write data. Locking a buffer with this flag will ALWAYS 
			    return a pointer to new, blank memory rather than the memory associated 
			    with the contents of the buffer; this avoids DMA stalls because you can 
			    write to a new memory area while the previous one is being used. 
			    */
			    HBU_WRITE_ONLY = 4,
                /** Indicates that the application will be refilling the contents
                of the buffer regularly (not just updating, but generating the
                contents from scratch), and therefore does not mind if the contents 
                of the buffer are lost somehow and need to be recreated. This
                allows and additional level of optimisation on the buffer.
                This option only really makes sense when combined with 
                HBU_DYNAMIC_WRITE_ONLY.
                */
                HBU_DISCARDABLE = 8,
				/// Combination of HBU_STATIC and HBU_WRITE_ONLY
				HBU_STATIC_WRITE_ONLY = 5, 
				/** Combination of HBU_DYNAMIC and HBU_WRITE_ONLY. If you use 
                this, strongly consider using HBU_DYNAMIC_WRITE_ONLY_DISCARDABLE
                instead if you update the entire contents of the buffer very 
                regularly. 
                */
				HBU_DYNAMIC_WRITE_ONLY = 6,
                /// Combination of HBU_DYNAMIC, HBU_WRITE_ONLY and HBU_DISCARDABLE
                HBU_DYNAMIC_WRITE_ONLY_DISCARDABLE = 14


		    };
		    /// Locking options
		    enum LockOptions
		    {
                /** Normal mode, ie allows read/write and contents are preserved. */
                HBL_NORMAL,
			    /** Discards the <em>entire</em> buffer while locking; this allows optimisation to be 
				performed because synchronisation issues are relaxed. Only allowed on buffers 
			    created with the HBU_DYNAMIC flag. 
			    */
			    HBL_DISCARD,
			    /** Lock the buffer for reading only. Not allowed in buffers which are created with HBU_WRITE_ONLY. 
				Mandatory on static buffers, i.e. those created without the HBU_DYNAMIC flag. 
				*/ 
			    HBL_READ_ONLY,
                /** As HBL_NORMAL, except the application guarantees not to overwrite any 
                region of the buffer which has already been used in this frame, can allow
                some optimisation on some APIs. */
                HBL_NO_OVERWRITE
    			
		    };
	    protected:
		    UINT32 mSizeInBytes;
		    Usage mUsage;
		    bool mIsLocked;
			UINT32 mLockStart;
			UINT32 mLockSize;
			bool mSystemMemory;
    		
            /// Internal implementation of lock()
		    virtual void* lockImpl(UINT32 offset, UINT32 length, LockOptions options) = 0;
            /// Internal implementation of unlock()
		    virtual void unlockImpl(void) = 0;

    public:
		    /// Constructor, to be called by HardwareBufferManager only
            HardwareBuffer(Usage usage, bool systemMemory) 
				: mUsage(usage), mIsLocked(false), mSystemMemory(systemMemory)
            {  }
            virtual ~HardwareBuffer() {}
		    /** Lock the buffer for (potentially) reading / writing.
		    @param offset The byte offset from the start of the buffer to lock
		    @param length The size of the area to lock, in bytes
		    @param options Locking options
		    @returns Pointer to the locked memory
		    */
		    virtual void* lock(UINT32 offset, UINT32 length, LockOptions options)
            {
                assert(!isLocked() && "Cannot lock this buffer, it is already locked!");
                void* ret = lockImpl(offset, length, options);
                mIsLocked = true;

				mLockStart = offset;
				mLockSize = length;
                return ret;
            }

            /** Lock the entire buffer for (potentially) reading / writing.
		    @param options Locking options
		    @returns Pointer to the locked memory
            */
            void* lock(LockOptions options)
            {
                return this->lock(0, mSizeInBytes, options);
            }
		    /** Releases the lock on this buffer. 
            @remarks 
                Locking and unlocking a buffer can, in some rare circumstances such as 
                switching video modes whilst the buffer is locked, corrupt the 
                contents of a buffer. This is pretty rare, but if it occurs, 
                this method will throw an exception, meaning you
                must re-upload the data.
            @par
                Note that using the 'read' and 'write' forms of updating the buffer does not
                suffer from this problem, so if you want to be 100% sure your
                data will not be lost, use the 'read' and 'write' forms instead.
            */
		    virtual void unlock(void)
            {
                assert(isLocked() && "Cannot unlock this buffer, it is not locked!");

                unlockImpl();
                mIsLocked = false;
            }

            /** Reads data from the buffer and places it in the memory pointed to by pDest.
		    @param offset The byte offset from the start of the buffer to read
		    @param length The size of the area to read, in bytes
            @param pDest The area of memory in which to place the data, must be large enough to 
                accommodate the data!
            */
            virtual void readData(UINT32 offset, UINT32 length, void* pDest) = 0;
            /** Writes data to the buffer from an area of system memory; note that you must
                ensure that your buffer is big enough.
		    @param offset The byte offset from the start of the buffer to start writing
		    @param length The size of the data to write to, in bytes
            @param pSource The source of the data to be written
			@param discardWholeBuffer If true, this allows the driver to discard the entire buffer when writing,
				such that DMA stalls can be avoided; use if you can.
            */
            virtual void writeData(UINT32 offset, UINT32 length, const void* pSource,
					bool discardWholeBuffer = false) = 0;

			/** Copy data from another buffer into this one.
			@remarks
				Note that the source buffer must not be created with the
                usage HBU_WRITE_ONLY otherwise this will fail. 
			@param srcBuffer The buffer from which to read the copied data
			@param srcOffset Offset in the source buffer at which to start reading
			@param dstOffset Offset in the destination buffer to start writing
			@param length Length of the data to copy, in bytes.
			@param discardWholeBuffer If true, will discard the entire contents of this buffer before copying
			*/
			virtual void copyData(HardwareBuffer& srcBuffer, UINT32 srcOffset, 
				UINT32 dstOffset, UINT32 length, bool discardWholeBuffer = false)
			{
				const void *srcData = srcBuffer.lock(
					srcOffset, length, HBL_READ_ONLY);
				this->writeData(dstOffset, length, srcData, discardWholeBuffer);
				srcBuffer.unlock();
			}

			/** Copy all data from another buffer into this one. 
			@remarks
				Normally these buffers should be of identical size, but if they're
				not, the routine will use the smallest of the two sizes.
			*/
			virtual void copyData(HardwareBuffer& srcBuffer)
			{
				UINT32 sz = std::min(getSizeInBytes(), srcBuffer.getSizeInBytes()); 
				copyData(srcBuffer, 0, 0, sz, true);
			}
			
            /// Returns the size of this buffer in bytes
            UINT32 getSizeInBytes(void) const { return mSizeInBytes; }
            /// Returns the Usage flags with which this buffer was created
            Usage getUsage(void) const { return mUsage; }
			/// Returns whether this buffer is held in system memory
			bool isSystemMemory(void) const { return mSystemMemory; }
            /// Returns whether or not this buffer is currently locked.
            bool isLocked(void) const { 
                return mIsLocked; 
            }	
    };
	/** @} */
	/** @} */
}
#endif