source: downloads/ogre/OgreMain/include/OgreHardwareBuffer.h @ 20

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

Copyright (c) 2000-2006 Torus Knot Software Ltd
Also see acknowledgements in Readme.html

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA, or go to
http://www.gnu.org/copyleft/lesser.txt.

You may alternatively use this source under the terms of a specific version of
the OGRE Unrestricted License provided you have obtained such a license from
Torus Knot Software Ltd.
-----------------------------------------------------------------------------
*/
#ifndef __HardwareBuffer__
#define __HardwareBuffer__

// Precompiler options
#include "OgrePrerequisites.h"

namespace Ogre {

    /** 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:
                    /// 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 statuc buffers, ie 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();
                        }

            /// 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