Qt 4.8: QGLBuffer Class Reference

Qt Reference Documentation

# QGLBuffer Class Reference

The QGLBuffer class provides functions for creating and managing GL buffer objects. More...

     #include <QGLBuffer>

This class was introduced in Qt 4.7.

- List of all members, including inherited members

## Public Types

enum | Access { ReadOnly, WriteOnly, ReadWrite }
enum | Type { VertexBuffer, IndexBuffer, PixelPackBuffer, PixelUnpackBuffer }
enum | UsagePattern { StreamDraw, StreamRead, StreamCopy, StaticDraw, ..., DynamicCopy }

## Public Functions

| QGLBuffer ()
| QGLBuffer ( QGLBuffer::Type type )
| QGLBuffer ( const QGLBuffer & other )
| ~QGLBuffer ()
void | allocate ( const void * data, int count )
void | allocate ( int count )
bool | bind ()
GLuint | bufferId () const
bool | create ()
void | destroy ()
bool | isCreated () const
void * | map ( QGLBuffer::Access access )
bool | read ( int offset, void * data, int count )
void | release ()
void | setUsagePattern ( QGLBuffer::UsagePattern value )
int | size () const
QGLBuffer::Type | type () const
bool | unmap ()
QGLBuffer::UsagePattern | usagePattern () const
void | write ( int offset, const void * data, int count )
QGLBuffer & | operator= ( const QGLBuffer & other )

## Static Public Members

void | release ( QGLBuffer::Type type )

## Detailed Description

The QGLBuffer class provides functions for creating and managing GL buffer objects.

Buffer objects are created in the GL server so that the client application can avoid uploading vertices, indices, texture image data, etc every time they are needed.

QGLBuffer objects can be copied around as a reference to the underlying GL buffer object:

     QGLBuffer buffer1(QGLBuffer::IndexBuffer);
     buffer1.create();

     QGLBuffer buffer2 = buffer1;

QGLBuffer performs a shallow copy when objects are copied in this manner, but does not implement copy-on-write semantics. The original object will be affected whenever the copy is modified.

## Member Type Documentation

### enum QGLBuffer::Access

This enum defines the access mode for QGLBuffer::map().

Constant | Value | Description
--- | --- | ---
`QGLBuffer::ReadOnly` | `0x88B8` | The buffer will be mapped for reading only.
`QGLBuffer::WriteOnly` | `0x88B9` | The buffer will be mapped for writing only.
`QGLBuffer::ReadWrite` | `0x88BA` | The buffer will be mapped for reading and writing.

### enum QGLBuffer::Type

This enum defines the type of GL buffer object to create with QGLBuffer.

Constant | Value | Description
--- | --- | ---
`QGLBuffer::VertexBuffer` | `0x8892` | Vertex buffer object for use when specifying vertex arrays.
`QGLBuffer::IndexBuffer` | `0x8893` | Index buffer object for use with `glDrawElements()`.
`QGLBuffer::PixelPackBuffer` | `0x88EB` | Pixel pack buffer object for reading pixel data from the GL server (for example, with `glReadPixels()`). Not supported under OpenGL/ES.
`QGLBuffer::PixelUnpackBuffer` | `0x88EC` | Pixel unpack buffer object for writing pixel data to the GL server (for example, with `glTexImage2D()`). Not supported under OpenGL/ES.

### enum QGLBuffer::UsagePattern

This enum defines the usage pattern of a QGLBuffer object.

Constant | Value | Description
--- | --- | ---
`QGLBuffer::StreamDraw` | `0x88E0` | The data will be set once and used a few times for drawing operations. Under OpenGL/ES 1.1 this is identical to StaticDraw.
`QGLBuffer::StreamRead` | `0x88E1` | The data will be set once and used a few times for reading data back from the GL server. Not supported under OpenGL/ES.
`QGLBuffer::StreamCopy` | `0x88E2` | The data will be set once and used a few times for reading data back from the GL server for use in further drawing operations. Not supported under OpenGL/ES.
`QGLBuffer::StaticDraw` | `0x88E4` | The data will be set once and used many times for drawing operations.
`QGLBuffer::StaticRead` | `0x88E5` | The data will be set once and used many times for reading data back from the GL server. Not supported under OpenGL/ES.
`QGLBuffer::StaticCopy` | `0x88E6` | The data will be set once and used many times for reading data back from the GL server for use in further drawing operations. Not supported under OpenGL/ES.
`QGLBuffer::DynamicDraw` | `0x88E8` | The data will be modified repeatedly and used many times for drawing operations.
`QGLBuffer::DynamicRead` | `0x88E9` | The data will be modified repeatedly and used many times for reading data back from the GL server. Not supported under OpenGL/ES.
`QGLBuffer::DynamicCopy` | `0x88EA` | The data will be modified repeatedly and used many times for reading data back from the GL server for use in further drawing operations. Not supported under OpenGL/ES.

## Member Function Documentation

### QGLBuffer::QGLBuffer ()

Constructs a new buffer object of type QGLBuffer::VertexBuffer.

Note: this constructor just creates the QGLBuffer instance. The actual buffer object in the GL server is not created until create() is called.

See also create().

### QGLBuffer::QGLBuffer ( QGLBuffer::Type type )

Constructs a new buffer object of type.

Note: this constructor just creates the QGLBuffer instance. The actual buffer object in the GL server is not created until create() is called.

See also create().

### QGLBuffer::QGLBuffer ( const QGLBuffer & other )

Constructs a shallow copy of other.

Note: QGLBuffer does not implement copy-on-write semantics, so other will be affected whenever the copy is modified.

### QGLBuffer::~QGLBuffer ()

Destroys this buffer object, including the storage being used in the GL server.

### void QGLBuffer::allocate ( const void * data, int count )

Allocates count bytes of space to the buffer, initialized to the contents of data. Any previous contents will be removed.

It is assumed that create() has been called on this buffer and that it has been bound to the current context.

See also create(), read(), and write().

### void QGLBuffer::allocate ( int count )

This is an overloaded function.

Allocates count bytes of space to the buffer. Any previous contents will be removed.

It is assumed that create() has been called on this buffer and that it has been bound to the current context.

See also create() and write().

### bool QGLBuffer::bind ()

Binds the buffer associated with this object to the current GL context. Returns false if binding was not possible, usually because type() is not supported on this GL implementation.

The buffer must be bound to the same QGLContext current when create() was called, or to another QGLContext that is sharing with it. Otherwise, false will be returned from this function.

See also release() and create().

### GLuint QGLBuffer::bufferId () const

Returns the GL identifier associated with this buffer; zero if the buffer has not been created.

See also isCreated().

### bool QGLBuffer::create ()

Creates the buffer object in the GL server. Returns true if the object was created; false otherwise.

This function must be called with a current QGLContext. The buffer will be bound to and can only be used in that context (or any other context that is shared with it).

This function will return false if the GL implementation does not support buffers, or there is no current QGLContext.

See also isCreated(), allocate(), write(), and destroy().

### void QGLBuffer::destroy ()

Destroys this buffer object, including the storage being used in the GL server. All references to the buffer will become invalid.

### bool QGLBuffer::isCreated () const

Returns true if this buffer has been created; false otherwise.

See also create() and destroy().

### void * QGLBuffer::map ( QGLBuffer::Access access )

Maps the contents of this buffer into the application's memory space and returns a pointer to it. Returns null if memory mapping is not possible. The access parameter indicates the type of access to be performed.

It is assumed that create() has been called on this buffer and that it has been bound to the current context.

This function is only supported under OpenGL/ES if the `GL_OES_mapbuffer` extension is present.

See also unmap(), create(), and bind().

### bool QGLBuffer::read ( int offset, void * data, int count )

Reads the count bytes in this buffer starting at offset into data. Returns true on success; false if reading from the buffer is not supported. Buffer reading is not supported under OpenGL/ES.

It is assumed that this buffer has been bound to the current context.

See also write() and bind().

### void QGLBuffer::release ()

Releases the buffer associated with this object from the current GL context.

This function must be called with the same QGLContext current as when bind() was called on the buffer.

See also bind().

### void QGLBuffer::release ( QGLBuffer::Type type )`[static]`

Releases the buffer associated with type in the current QGLContext.

This function is a direct call to `glBindBuffer(type, 0)` for use when the caller does not know which QGLBuffer has been bound to the context but wants to make sure that it is released.

     QGLBuffer::release(QGLBuffer::VertexBuffer);

### void QGLBuffer::setUsagePattern ( QGLBuffer::UsagePattern value )

Sets the usage pattern for this buffer object to value. This function must be called before allocate() or write().

See also usagePattern(), allocate(), and write().

### int QGLBuffer::size () const

Returns the size of the data in this buffer, for reading operations. Returns -1 if fetching the buffer size is not supported, or the buffer has not been created.

It is assumed that this buffer has been bound to the current context.

See also isCreated() and bind().

### QGLBuffer::Type QGLBuffer::type () const

Returns the type of buffer represented by this object.

### bool QGLBuffer::unmap ()

Unmaps the buffer after it was mapped into the application's memory space with a previous call to map(). Returns true if the unmap succeeded; false otherwise.

It is assumed that this buffer has been bound to the current context, and that it was previously mapped with map().

This function is only supported under OpenGL/ES if the `GL_OES_mapbuffer` extension is present.

See also map().

### QGLBuffer::UsagePattern QGLBuffer::usagePattern () const

Returns the usage pattern for this buffer object. The default value is StaticDraw.

See also setUsagePattern().

### void QGLBuffer::write ( int offset, const void * data, int count )

Replaces the count bytes of this buffer starting at offset with the contents of data. Any other bytes in the buffer will be left unmodified.

It is assumed that create() has been called on this buffer and that it has been bound to the current context.

See also create(), read(), and allocate().

### QGLBuffer & QGLBuffer::operator= ( const QGLBuffer & other )

Assigns a shallow copy of other to this object.

Note: QGLBuffer does not implement copy-on-write semantics, so other will be affected whenever the copy is modified.