Ogre::HardwareBuffer Class Reference

Abstract class defining common features of hardware buffers. More...

#include <OgreHardwareBuffer.h>

Inheritance diagram for Ogre::HardwareBuffer:

Public Types
enum	LockOptions {   HBL_NORMAL , HBL_DISCARD , HBL_READ_ONLY , HBL_NO_OVERWRITE ,   HBL_WRITE_ONLY }
	Locking options. More...
enum	Usage {   HBU_STATIC = 1 , HBU_DYNAMIC = 2 , HBU_WRITE_ONLY = 4 , HBU_DISCARDABLE = 8 ,   HBU_STATIC_WRITE_ONLY = HBU_STATIC | HBU_WRITE_ONLY , HBU_DYNAMIC_WRITE_ONLY = HBU_DYNAMIC | HBU_WRITE_ONLY , HBU_DYNAMIC_WRITE_ONLY_DISCARDABLE = HBU_DYNAMIC_WRITE_ONLY | HBU_DISCARDABLE }
	Enums describing buffer usage; not mutually exclusive. More...

Public Member Functions
	HardwareBuffer (Usage usage, bool systemMemory, bool useShadowBuffer)
	Constructor, to be called by HardwareBufferManager only.
virtual	~HardwareBuffer ()
virtual void	_updateFromShadow (void)
	Updates the real buffer from the shadow buffer, if required.
virtual void	copyData (HardwareBuffer &srcBuffer)
	Copy all data from another buffer into this one.
virtual void	copyData (HardwareBuffer &srcBuffer, size_t srcOffset, size_t dstOffset, size_t length, bool discardWholeBuffer=false)
	Copy data from another buffer into this one.
size_t	getSizeInBytes (void) const
	Returns the size of this buffer in bytes.
Usage	getUsage (void) const
	Returns the Usage flags with which this buffer was created.
bool	hasShadowBuffer (void) const
	Returns whether this buffer has a system memory shadow for quicker reading.
bool	isLocked (void) const
	Returns whether or not this buffer is currently locked.
bool	isSystemMemory (void) const
	Returns whether this buffer is held in system memory.
void *	lock (LockOptions options)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
virtual void *	lock (size_t offset, size_t length, LockOptions options)
	Lock the buffer for (potentially) reading / writing.
virtual void	readData (size_t offset, size_t length, void *pDest)=0
	Reads data from the buffer and places it in the memory pointed to by pDest.
void	suppressHardwareUpdate (bool suppress)
	Pass true to suppress hardware upload of shadow buffer changes.
virtual void	unlock (void)
	Releases the lock on this buffer.
virtual void	writeData (size_t offset, size_t length, const void *pSource, bool discardWholeBuffer=false)=0
	Writes data to the buffer from an area of system memory; note that you must ensure that your buffer is big enough.

Detailed Description

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.

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.

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.

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 its 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.

Member Enumeration Documentation

Usage

enum Ogre::HardwareBuffer::Usage

Enums describing buffer usage; not mutually exclusive.

Enumerator
HBU_STATIC	Static buffer which the application rarely modifies once created. Modifying the contents of this buffer will involve a performance hit.
HBU_DYNAMIC	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. This is the least optimal buffer setting.
HBU_WRITE_ONLY	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. However, you may read from it’s shadow buffer if you set one up
HBU_DISCARDABLE	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_STATIC_WRITE_ONLY	Combination of HBU_STATIC and HBU_WRITE_ONLY This is the optimal buffer usage setting.
HBU_DYNAMIC_WRITE_ONLY	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_DISCARDABLE	Combination of HBU_DYNAMIC, HBU_WRITE_ONLY and HBU_DISCARDABLE This means that you expect to replace the entire contents of the buffer on an extremely regular basis, most likely every frame. By selecting this option, you free the system up from having to be concerned about losing the existing contents of the buffer at any time, because if it does lose them, you will be replacing them next frame anyway. On some platforms this can make a significant performance difference, so you should try to use this whenever you have a buffer you need to update regularly. Note that if you create a buffer this way, you should use the HBL_DISCARD flag when locking the contents of it for writing.

LockOptions

enum Ogre::HardwareBuffer::LockOptions

Locking options.

Enumerator
HBL_NORMAL	Normal mode, ie allows read/write and contents are preserved. This kind of lock allows reading and writing from the buffer - it’s also the least optimal because basically you’re telling the card you could be doing anything at all. If you’re not using a shadow buffer, it requires the buffer to be transferred from the card and back again. If you’re using a shadow buffer the effect is minimal.
HBL_DISCARD	Discards the entire buffer while locking. This means you are happy for the card to discard the entire current contents of the buffer. Implicitly this means you are not going to read the data - it also means that the card can avoid any stalls if the buffer is currently being rendered from, because it will actually give you an entirely different one. Use this wherever possible when you are locking a buffer which was not created with a shadow buffer. If you are using a shadow buffer it matters less, although with a shadow buffer it’s preferable to lock the entire buffer at once, because that allows the shadow buffer to use HBL_DISCARD when it uploads the updated contents to the real buffer. Only allowed on buffers created with the HBU_DYNAMIC flag.
HBL_READ_ONLY	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_NO_OVERWRITE	As HBL_DISCARD, 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. This is only useful on buffers with no shadow buffer.
HBL_WRITE_ONLY	Lock the buffer for writing only.

Constructor & Destructor Documentation

HardwareBuffer()

Ogre::HardwareBuffer::HardwareBuffer ( Usage  usage, bool  systemMemory, bool  useShadowBuffer  )

inline

Constructor, to be called by HardwareBufferManager only.

~HardwareBuffer()

virtual Ogre::HardwareBuffer::~HardwareBuffer ( )

inlinevirtual

Member Function Documentation

lock() [1/2]

virtual void * Ogre::HardwareBuffer::lock ( size_t  offset, size_t  length, LockOptions  options  )

inlinevirtual

Lock the buffer for (potentially) reading / writing.

Parameters

offset	The byte offset from the start of the buffer to lock
length	The size of the area to lock, in bytes
options	Locking options

Returns

Pointer to the locked memory

Reimplemented in Ogre::DefaultHardwareVertexBuffer, Ogre::DefaultHardwareIndexBuffer, Ogre::DefaultHardwareUniformBuffer, Ogre::DefaultHardwareCounterBuffer, Ogre::HardwarePixelBuffer, Ogre::HardwarePixelBuffer, Ogre::D3D11HardwareIndexBuffer, Ogre::D3D11HardwareUniformBuffer, and Ogre::D3D11HardwareVertexBuffer.

References OGRE_EXCEPT.

Referenced by copyData(), and Ogre::HardwareBufferLockGuard::lock().

lock() [2/2]

void * Ogre::HardwareBuffer::lock ( LockOptions  options )

inline

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

unlock()

virtual void Ogre::HardwareBuffer::unlock ( void  )

inlinevirtual

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.

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.

Reimplemented in Ogre::DefaultHardwareVertexBuffer, Ogre::DefaultHardwareIndexBuffer, Ogre::DefaultHardwareUniformBuffer, Ogre::DefaultHardwareCounterBuffer, Ogre::D3D11HardwareIndexBuffer, Ogre::D3D11HardwareUniformBuffer, and Ogre::D3D11HardwareVertexBuffer.

Referenced by copyData(), and Ogre::HardwareBufferLockGuard::unlock().

readData()

virtual void Ogre::HardwareBuffer::readData ( size_t  offset, size_t  length, void *  pDest  )

pure virtual

Reads data from the buffer and places it in the memory pointed to by pDest.

Parameters

offset	The byte offset from the start of the buffer to read
length	The size of the area to read, in bytes
pDest	The area of memory in which to place the data, must be large enough to accommodate the data!

Implemented in Ogre::DefaultHardwareVertexBuffer, Ogre::DefaultHardwareIndexBuffer, Ogre::DefaultHardwareUniformBuffer, Ogre::DefaultHardwareCounterBuffer, Ogre::HardwarePixelBuffer, Ogre::D3D11HardwareBuffer, Ogre::D3D11HardwareIndexBuffer, Ogre::D3D11HardwareUniformBuffer, Ogre::D3D11HardwareVertexBuffer, Ogre::D3D9HardwareIndexBuffer, Ogre::D3D9HardwareVertexBuffer, Ogre::GLHardwareIndexBuffer, Ogre::GLHardwareVertexBuffer, Ogre::GL3PlusHardwareCounterBuffer, Ogre::GL3PlusHardwareIndexBuffer, Ogre::GL3PlusHardwareShaderStorageBuffer, Ogre::GL3PlusHardwareUniformBuffer, Ogre::GL3PlusHardwareVertexBuffer, Ogre::GLES2HardwareIndexBuffer, Ogre::GLES2HardwareUniformBuffer, and Ogre::GLES2HardwareVertexBuffer.

writeData()

virtual void Ogre::HardwareBuffer::writeData ( size_t  offset, size_t  length, const void *  pSource, bool  discardWholeBuffer = false  )

pure virtual

Writes data to the buffer from an area of system memory; note that you must ensure that your buffer is big enough.

Parameters

offset	The byte offset from the start of the buffer to start writing
length	The size of the data to write to, in bytes
pSource	The source of the data to be written
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.

Implemented in Ogre::DefaultHardwareVertexBuffer, Ogre::DefaultHardwareIndexBuffer, Ogre::DefaultHardwareUniformBuffer, Ogre::DefaultHardwareCounterBuffer, Ogre::HardwarePixelBuffer, Ogre::D3D11HardwareBuffer, Ogre::D3D11HardwareIndexBuffer, Ogre::D3D11HardwareUniformBuffer, Ogre::D3D11HardwareVertexBuffer, Ogre::D3D9HardwareIndexBuffer, Ogre::D3D9HardwareVertexBuffer, Ogre::GLHardwareIndexBuffer, Ogre::GLHardwareVertexBuffer, Ogre::GL3PlusHardwareCounterBuffer, Ogre::GL3PlusHardwareIndexBuffer, Ogre::GL3PlusHardwareShaderStorageBuffer, Ogre::GL3PlusHardwareUniformBuffer, Ogre::GL3PlusHardwareVertexBuffer, Ogre::GLES2HardwareIndexBuffer, Ogre::GLES2HardwareUniformBuffer, and Ogre::GLES2HardwareVertexBuffer.

copyData() [1/2]

virtual void Ogre::HardwareBuffer::copyData ( HardwareBuffer &  srcBuffer, size_t  srcOffset, size_t  dstOffset, size_t  length, bool  discardWholeBuffer = false  )

inlinevirtual

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.

Parameters

srcBuffer	The buffer from which to read the copied data
srcOffset	Offset in the source buffer at which to start reading
dstOffset	Offset in the destination buffer to start writing
length	Length of the data to copy, in bytes.
discardWholeBuffer	If true, will discard the entire contents of this buffer before copying

Reimplemented in Ogre::D3D11HardwareBuffer, Ogre::D3D11HardwareIndexBuffer, Ogre::D3D11HardwareUniformBuffer, Ogre::D3D11HardwareVertexBuffer, Ogre::GL3PlusHardwareCounterBuffer, Ogre::GL3PlusHardwareIndexBuffer, Ogre::GL3PlusHardwareShaderStorageBuffer, Ogre::GL3PlusHardwareUniformBuffer, Ogre::GL3PlusHardwareVertexBuffer, Ogre::GLES2HardwareIndexBuffer, Ogre::GLES2HardwareUniformBuffer, and Ogre::GLES2HardwareVertexBuffer.

References lock(), and unlock().

copyData() [2/2]

virtual void Ogre::HardwareBuffer::copyData ( HardwareBuffer &  srcBuffer )

inlinevirtual

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.

References getSizeInBytes().

_updateFromShadow()

virtual void Ogre::HardwareBuffer::_updateFromShadow ( void  )

inlinevirtual

Updates the real buffer from the shadow buffer, if required.

Reimplemented in Ogre::D3D11HardwareBuffer, Ogre::GLHardwareIndexBuffer, Ogre::GLHardwareVertexBuffer, Ogre::GL3PlusHardwareIndexBuffer, Ogre::GL3PlusHardwareVertexBuffer, Ogre::GLES2HardwareIndexBuffer, and Ogre::GLES2HardwareVertexBuffer.

getSizeInBytes()

size_t Ogre::HardwareBuffer::getSizeInBytes ( void  ) const

inline

Returns the size of this buffer in bytes.

Referenced by copyData().

getUsage()

Usage Ogre::HardwareBuffer::getUsage ( void  ) const

inline

Returns the Usage flags with which this buffer was created.

isSystemMemory()

bool Ogre::HardwareBuffer::isSystemMemory ( void  ) const

inline

Returns whether this buffer is held in system memory.

hasShadowBuffer()

bool Ogre::HardwareBuffer::hasShadowBuffer ( void  ) const

inline

Returns whether this buffer has a system memory shadow for quicker reading.

isLocked()

bool Ogre::HardwareBuffer::isLocked ( void  ) const

inline

Returns whether or not this buffer is currently locked.

suppressHardwareUpdate()

void Ogre::HardwareBuffer::suppressHardwareUpdate ( bool  suppress )

inline

Pass true to suppress hardware upload of shadow buffer changes.

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The documentation for this class was generated from the following file:

• OgreHardwareBuffer.h