source: GTP/trunk/App/Demos/Geom/OgreStuff/include/OgreHardwareBuffer.h @ 1812

Revision 1812, 14.6 KB checked in by gumbau, 18 years ago (diff)
RevLine 
[1812]1/*
2-----------------------------------------------------------------------------
3This source file is part of OGRE
4    (Object-oriented Graphics Rendering Engine)
5For the latest info, see http://www.ogre3d.org/
6
7Copyright (c) 2000-2005 The OGRE Team
8Also see acknowledgements in Readme.html
9
10This program is free software; you can redistribute it and/or modify it under
11the terms of the GNU Lesser General Public License as published by the Free Software
12Foundation; either version 2 of the License, or (at your option) any later
13version.
14
15This program is distributed in the hope that it will be useful, but WITHOUT
16ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
17FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
18
19You should have received a copy of the GNU Lesser General Public License along with
20this program; if not, write to the Free Software Foundation, Inc., 59 Temple
21Place - Suite 330, Boston, MA 02111-1307, USA, or go to
22http://www.gnu.org/copyleft/lesser.txt.
23-----------------------------------------------------------------------------
24*/
25#ifndef __HardwareBuffer__
26#define __HardwareBuffer__
27
28// Precompiler options
29#include "OgrePrerequisites.h"
30
31namespace Ogre {
32
33    /** Abstract class defining common features of hardware buffers.
34    @remarks
35            A 'hardware buffer' is any area of memory held outside of core system ram,
36            and in our case refers mostly to video ram, although in theory this class
37            could be used with other memory areas such as sound card memory, custom
38            coprocessor memory etc.
39    @par
40            This reflects the fact that memory held outside of main system RAM must
41            be interacted with in a more formal fashion in order to promote
42            cooperative and optimal usage of the buffers between the various
43            processing units which manipulate them.
44    @par
45            This abstract class defines the core interface which is common to all
46            buffers, whether it be vertex buffers, index buffers, texture memory
47            or framebuffer memory etc.
48        @par
49                Buffers have the ability to be 'shadowed' in system memory, this is because
50                the kinds of access allowed on hardware buffers is not always as flexible as
51                that allowed for areas of system memory - for example it is often either
52                impossible, or extremely undesirable from a performance standpoint to read from
53                a hardware buffer; when writing to hardware buffers, you should also write every
54                byte and do it sequentially. In situations where this is too restrictive,
55                it is possible to create a hardware, write-only buffer (the most efficient kind)
56                and to back it with a system memory 'shadow' copy which can be read and updated arbitrarily.
57                Ogre handles synchronising this buffer with the real hardware buffer (which should still be
58                created with the HBU_DYNAMIC flag if you intend to update it very frequently). Whilst this
59                approach does have it's own costs, such as increased memory overhead, these costs can
60                often be outweighed by the performance benefits of using a more hardware efficient buffer.
61                You should look for the 'useShadowBuffer' parameter on the creation methods used to create
62                the buffer of the type you require (see HardwareBufferManager) to enable this feature.
63    */
64    class _OgreExport HardwareBuffer
65    {
66
67            public:
68                    /// Enums describing buffer usage; not mutually exclusive
69                    enum Usage
70                    {
71                /** Static buffer which the application rarely modifies once created. Modifying
72                the contents of this buffer will involve a performance hit.
73                */
74                HBU_STATIC = 1,
75                            /** Indicates the application would like to modify this buffer with the CPU
76                            fairly often.
77                            Buffers created with this flag will typically end up in AGP memory rather
78                            than video memory.
79                            */
80                            HBU_DYNAMIC = 2,
81                            /** Indicates the application will never read the contents of the buffer back,
82                            it will only ever write data. Locking a buffer with this flag will ALWAYS
83                            return a pointer to new, blank memory rather than the memory associated
84                            with the contents of the buffer; this avoids DMA stalls because you can
85                            write to a new memory area while the previous one is being used.
86                            */
87                            HBU_WRITE_ONLY = 4,
88                /** Indicates that the application will be refilling the contents
89                of the buffer regularly (not just updating, but generating the
90                contents from scratch), and therefore does not mind if the contents
91                of the buffer are lost somehow and need to be recreated. This
92                allows and additional level of optimisation on the buffer.
93                This option only really makes sense when combined with
94                HBU_DYNAMIC_WRITE_ONLY.
95                */
96                HBU_DISCARDABLE = 8,
97                                /// Combination of HBU_STATIC and HBU_WRITE_ONLY
98                                HBU_STATIC_WRITE_ONLY = 5,
99                                /** Combination of HBU_DYNAMIC and HBU_WRITE_ONLY. If you use
100                this, strongly consider using HBU_DYNAMIC_WRITE_ONLY_DISCARDABLE
101                instead if you update the entire contents of the buffer very
102                regularly.
103                */
104                                HBU_DYNAMIC_WRITE_ONLY = 6,
105                /// Combination of HBU_DYNAMIC, HBU_WRITE_ONLY and HBU_DISCARDABLE
106                HBU_DYNAMIC_WRITE_ONLY_DISCARDABLE = 14
107
108
109                    };
110                    /// Locking options
111                    enum LockOptions
112                    {
113                /** Normal mode, ie allows read/write and contents are preserved. */
114                HBL_NORMAL,
115                            /** Discards the <em>entire</em> buffer while locking; this allows optimisation to be
116                                performed because synchronisation issues are relaxed. Only allowed on buffers
117                            created with the HBU_DYNAMIC flag.
118                            */
119                            HBL_DISCARD,
120                            /** Lock the buffer for reading only. Not allowed in buffers which are created with HBU_WRITE_ONLY.
121                                Mandatory on statuc buffers, ie those created without the HBU_DYNAMIC flag.
122                                */
123                            HBL_READ_ONLY,
124                /** As HBL_NORMAL, except the application guarantees not to overwrite any
125                region of the buffer which has already been used in this frame, can allow
126                some optimisation on some APIs. */
127                HBL_NO_OVERWRITE
128                       
129                    };
130            protected:
131                    size_t mSizeInBytes;
132                    Usage mUsage;
133                    bool mIsLocked;
134                        size_t mLockStart;
135                        size_t mLockSize;
136                        bool mSystemMemory;
137            bool mUseShadowBuffer;
138            HardwareBuffer* mpShadowBuffer;
139            bool mShadowUpdated;
140            bool mSuppressHardwareUpdate;
141               
142            /// Internal implementation of lock()
143                    virtual void* lockImpl(size_t offset, size_t length, LockOptions options) = 0;
144            /// Internal implementation of unlock()
145                    virtual void unlockImpl(void) = 0;
146
147    public:
148                    /// Constructor, to be called by HardwareBufferManager only
149            HardwareBuffer(Usage usage, bool systemMemory, bool useShadowBuffer)
150                                : mUsage(usage), mIsLocked(false), mSystemMemory(systemMemory),
151                mUseShadowBuffer(useShadowBuffer), mpShadowBuffer(NULL), mShadowUpdated(false),
152                mSuppressHardwareUpdate(false)
153            {
154                // If use shadow buffer, upgrade to WRITE_ONLY on hardware side
155                if (useShadowBuffer && usage == HBU_DYNAMIC)
156                {
157                    mUsage = HBU_DYNAMIC_WRITE_ONLY;
158                }
159                else if (useShadowBuffer && usage == HBU_STATIC)
160                {
161                    mUsage = HBU_STATIC_WRITE_ONLY;
162                }
163            }
164            virtual ~HardwareBuffer() {}
165                    /** Lock the buffer for (potentially) reading / writing.
166                    @param offset The byte offset from the start of the buffer to lock
167                    @param length The size of the area to lock, in bytes
168                    @param options Locking options
169                    @returns Pointer to the locked memory
170                    */
171                    virtual void* lock(size_t offset, size_t length, LockOptions options)
172            {
173                assert(!isLocked() && "Cannot lock this buffer, it is already locked!");
174                void* ret;
175                                if (mUseShadowBuffer)
176                {
177                                        if (options != HBL_READ_ONLY)
178                                        {
179                                                // we have to assume a read / write lock so we use the shadow buffer
180                                                // and tag for sync on unlock()
181                        mShadowUpdated = true;
182                    }
183
184                    ret = mpShadowBuffer->lock(offset, length, options);
185                }
186                else
187                {
188                                        // Lock the real buffer if there is no shadow buffer
189                    ret = lockImpl(offset, length, options);
190                    mIsLocked = true;
191                }
192                                mLockStart = offset;
193                                mLockSize = length;
194                return ret;
195            }
196
197            /** Lock the entire buffer for (potentially) reading / writing.
198                    @param options Locking options
199                    @returns Pointer to the locked memory
200            */
201            void* lock(LockOptions options)
202            {
203                return this->lock(0, mSizeInBytes, options);
204            }
205                    /** Releases the lock on this buffer.
206            @remarks
207                Locking and unlocking a buffer can, in some rare circumstances such as
208                switching video modes whilst the buffer is locked, corrupt the
209                contents of a buffer. This is pretty rare, but if it occurs,
210                this method will throw an exception, meaning you
211                must re-upload the data.
212            @par
213                Note that using the 'read' and 'write' forms of updating the buffer does not
214                suffer from this problem, so if you want to be 100% sure your
215                data will not be lost, use the 'read' and 'write' forms instead.
216            */
217                    virtual void unlock(void)
218            {
219                assert(isLocked() && "Cannot unlock this buffer, it is not locked!");
220
221                                // If we used the shadow buffer this time...
222                if (mUseShadowBuffer && mpShadowBuffer->isLocked())
223                {
224                    mpShadowBuffer->unlock();
225                    // Potentially update the 'real' buffer from the shadow buffer
226                    _updateFromShadow();
227                }
228                else
229                {
230                                        // Otherwise, unlock the real one
231                    unlockImpl();
232                    mIsLocked = false;
233                }
234
235            }
236
237            /** Reads data from the buffer and places it in the memory pointed to by pDest.
238                    @param offset The byte offset from the start of the buffer to read
239                    @param length The size of the area to read, in bytes
240            @param pDest The area of memory in which to place the data, must be large enough to
241                accommodate the data!
242            */
243            virtual void readData(size_t offset, size_t length, void* pDest) = 0;
244            /** Writes data to the buffer from an area of system memory; note that you must
245                ensure that your buffer is big enough.
246                    @param offset The byte offset from the start of the buffer to start writing
247                    @param length The size of the data to write to, in bytes
248            @param pSource The source of the data to be written
249                        @param discardWholeBuffer If true, this allows the driver to discard the entire buffer when writing,
250                                such that DMA stalls can be avoided; use if you can.
251            */
252            virtual void writeData(size_t offset, size_t length, const void* pSource,
253                                        bool discardWholeBuffer = false) = 0;
254
255                        /** Copy data from another buffer into this one.
256                        @remarks
257                                Note that the source buffer must not be created with the
258                usage HBU_WRITE_ONLY otherwise this will fail.
259                        @param srcBuffer The buffer from which to read the copied data
260                        @param srcOffset Offset in the source buffer at which to start reading
261                        @param dstOffset Offset in the destination buffer to start writing
262                        @param length Length of the data to copy, in bytes.
263                        @param discardWholeBuffer If true, will discard the entire contents of this buffer before copying
264                        */
265                        virtual void copyData(HardwareBuffer& srcBuffer, size_t srcOffset,
266                                size_t dstOffset, size_t length, bool discardWholeBuffer = false)
267                        {
268                                const void *srcData = srcBuffer.lock(
269                                        srcOffset, length, HBL_READ_ONLY);
270                                this->writeData(dstOffset, length, srcData, discardWholeBuffer);
271                                srcBuffer.unlock();
272                        }
273
274            /// Updates the real buffer from the shadow buffer, if required
275            virtual void _updateFromShadow(void)
276            {
277                if (mUseShadowBuffer && mShadowUpdated && !mSuppressHardwareUpdate)
278                {
279                    // Do this manually to avoid locking problems
280                    const void *srcData = mpShadowBuffer->lockImpl(
281                                        mLockStart, mLockSize, HBL_READ_ONLY);
282                                        // Lock with discard if the whole buffer was locked, otherwise normal
283                                        LockOptions lockOpt;
284                                        if (mLockStart == 0 && mLockSize == mSizeInBytes)
285                                                lockOpt = HBL_DISCARD;
286                                        else
287                                                lockOpt = HBL_NORMAL;
288                                       
289                    void *destData = this->lockImpl(
290                                        mLockStart, mLockSize, lockOpt);
291                                        // Copy shadow to real
292                    memcpy(destData, srcData, mLockSize);
293                    this->unlockImpl();
294                    mpShadowBuffer->unlockImpl();
295                    mShadowUpdated = false;
296                }
297            }
298
299            /// Returns the size of this buffer in bytes
300            size_t getSizeInBytes(void) const { return mSizeInBytes; }
301            /// Returns the Usage flags with which this buffer was created
302            Usage getUsage(void) const { return mUsage; }
303                        /// Returns whether this buffer is held in system memory
304                        bool isSystemMemory(void) const { return mSystemMemory; }
305                        /// Returns whether this buffer has a system memory shadow for quicker reading
306                        bool hasShadowBuffer(void) const { return mUseShadowBuffer; }
307            /// Returns whether or not this buffer is currently locked.
308            bool isLocked(void) const {
309                return mIsLocked || (mUseShadowBuffer && mpShadowBuffer->isLocked());
310            }
311            /// Pass true to suppress hardware upload of shadow buffer changes
312            void suppressHardwareUpdate(bool suppress) {
313                mSuppressHardwareUpdate = suppress;
314                if (!suppress)
315                    _updateFromShadow();
316            }
317
318
319
320
321               
322    };
323}
324#endif
325
326
Note: See TracBrowser for help on using the repository browser.