text: /*
  -----------------------------------------------------------------------------
  This source file is part of OGRE
      (Object-oriented Graphics Rendering Engine)
  For the latest info, see http://www.ogre3d.org/
  
  Copyright (c) 2000-2009 Torus Knot Software Ltd
  
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
  
  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.
  
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  THE SOFTWARE.
  -----------------------------------------------------------------------------
  */
  #ifndef __HardwareBuffer__
  #define __HardwareBuffer__
  
  // Precompiler options
  #include "OgrePrerequisites.h"
  
  namespace Ogre {
  
  	/** \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 _OgreExport HardwareBuffer : public BufferAlloc
      {
  
  	    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:
  		    size_t mSizeInBytes;
  		    Usage mUsage;
  		    bool mIsLocked;
  			size_t mLockStart;
  			size_t mLockSize;
  			bool mSystemMemory;
              bool mUseShadowBuffer;
              HardwareBuffer* mpShadowBuffer;
              bool mShadowUpdated;
              bool mSuppressHardwareUpdate;
      		
              /// Internal implementation of lock()
  		    virtual void* lockImpl(size_t offset, size_t 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, bool useShadowBuffer) 
  				: mUsage(usage), mIsLocked(false), mSystemMemory(systemMemory), 
                  mUseShadowBuffer(useShadowBuffer), mpShadowBuffer(NULL), mShadowUpdated(false), 
                  mSuppressHardwareUpdate(false) 
              {
                  // If use shadow buffer, upgrade to WRITE_ONLY on hardware side
                  if (useShadowBuffer && usage == HBU_DYNAMIC)
                  {
                      mUsage = HBU_DYNAMIC_WRITE_ONLY;
                  }
                  else if (useShadowBuffer && usage == HBU_STATIC)
                  {
                      mUsage = HBU_STATIC_WRITE_ONLY;
                  }
              }
              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(size_t offset, size_t length, LockOptions options)
              {
                  assert(!isLocked() && "Cannot lock this buffer, it is already locked!");
                  void* ret;
  				if (mUseShadowBuffer)
                  {
  					if (options != HBL_READ_ONLY)
  					{
  						// we have to assume a read / write lock so we use the shadow buffer
  						// and tag for sync on unlock()
                          mShadowUpdated = true;
                      }
  
                      ret = mpShadowBuffer->lock(offset, length, options);
                  }
                  else
                  {
  					// Lock the real buffer if there is no shadow buffer 
                      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!");
  
  				// If we used the shadow buffer this time...
                  if (mUseShadowBuffer && mpShadowBuffer->isLocked())
                  {
                      mpShadowBuffer->unlock();
                      // Potentially update the 'real' buffer from the shadow buffer
                      _updateFromShadow();
                  }
                  else
                  {
  					// Otherwise, unlock the real one
                      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(size_t offset, size_t 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(size_t offset, size_t 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, size_t srcOffset, 
  				size_t dstOffset, size_t 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)
  			{
  				size_t sz = std::min(getSizeInBytes(), srcBuffer.getSizeInBytes()); 
  				copyData(srcBuffer, 0, 0, sz, true);
  			}
  			
  			/// Updates the real buffer from the shadow buffer, if required
              virtual void _updateFromShadow(void)
              {
                  if (mUseShadowBuffer && mShadowUpdated && !mSuppressHardwareUpdate)
                  {
                      // Do this manually to avoid locking problems
                      const void *srcData = mpShadowBuffer->lockImpl(
      					mLockStart, mLockSize, HBL_READ_ONLY);
  					// Lock with discard if the whole buffer was locked, otherwise normal
  					LockOptions lockOpt;
  					if (mLockStart == 0 && mLockSize == mSizeInBytes)
  						lockOpt = HBL_DISCARD;
  					else
  						lockOpt = HBL_NORMAL;
  					
                      void *destData = this->lockImpl(
      					mLockStart, mLockSize, lockOpt);
  					// Copy shadow to real
                      memcpy(destData, srcData, mLockSize);
                      this->unlockImpl();
                      mpShadowBuffer->unlockImpl();
                      mShadowUpdated = false;
                  }
              }
  
              /// Returns the size of this buffer in bytes
              size_t 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 this buffer has a system memory shadow for quicker reading
  			bool hasShadowBuffer(void) const { return mUseShadowBuffer; }
              /// Returns whether or not this buffer is currently locked.
              bool isLocked(void) const { 
                  return mIsLocked || (mUseShadowBuffer && mpShadowBuffer->isLocked()); 
              }
              /// Pass true to suppress hardware upload of shadow buffer changes
              void suppressHardwareUpdate(bool suppress) {
                  mSuppressHardwareUpdate = suppress;
                  if (!suppress)
                      _updateFromShadow();
              }
  
  
  
  
      		
      };
  	/** @} */
  	/** @} */
  }
  #endif
  
  
  