- Qt 6.4
- Qt OpenGL
- C++ Classes
- QOpenGLBuffer
- Qt 6.4.2 Reference Documentation

# QOpenGLBuffer Class

The QOpenGLBuffer class provides functions for creating and managing OpenGL buffer objects. More...

Header: | #include <QOpenGLBuffer>
CMake: | find_package(Qt6 REQUIRED COMPONENTS OpenGL) target_link_libraries(mytarget PRIVATE Qt6::OpenGL)
qmake: | QT += opengl
Since: | Qt 5.0

- List of all members, including inherited members

## Public Types

enum | Access { ReadOnly, WriteOnly, ReadWrite }
enum | RangeAccessFlag { RangeRead, RangeWrite, RangeInvalidate, RangeInvalidateBuffer, RangeFlushExplicit, RangeUnsynchronized }
flags | RangeAccessFlags
enum | Type { VertexBuffer, IndexBuffer, PixelPackBuffer, PixelUnpackBuffer }
enum | UsagePattern { StreamDraw, StreamRead, StreamCopy, StaticDraw, StaticRead, …, DynamicCopy }

## Public Functions

| QOpenGLBuffer(const QOpenGLBuffer &other)
| QOpenGLBuffer(QOpenGLBuffer::Type type)
| QOpenGLBuffer()
QOpenGLBuffer & | operator=(const QOpenGLBuffer &other)
| ~QOpenGLBuffer()
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(QOpenGLBuffer::Access access)
void * | mapRange(int offset, int count, QOpenGLBuffer::RangeAccessFlags access)
bool | read(int offset, void *data, int count)
void | release()
void | setUsagePattern(QOpenGLBuffer::UsagePattern value)
int | size() const
QOpenGLBuffer::Type | type() const
bool | unmap()
QOpenGLBuffer::UsagePattern | usagePattern() const
void | write(int offset, const void *data, int count)

## Static Public Members

void | release(QOpenGLBuffer::Type type)

## Detailed Description

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

QOpenGLBuffer objects can be copied around as a reference to the underlying OpenGL buffer object:

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

     QOpenGLBuffer buffer2 = buffer1;

QOpenGLBuffer 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 QOpenGLBuffer::Access

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

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

### enum QOpenGLBuffer::RangeAccessFlag
flags QOpenGLBuffer::RangeAccessFlags

This enum defines the access mode bits for QOpenGLBuffer::mapRange().

Constant | Value | Description
--- | --- | ---
`QOpenGLBuffer::RangeRead` | `0x0001` | The buffer will be mapped for reading.
`QOpenGLBuffer::RangeWrite` | `0x0002` | The buffer will be mapped for writing.
`QOpenGLBuffer::RangeInvalidate` | `0x0004` | Discard the previous contents of the specified range.
`QOpenGLBuffer::RangeInvalidateBuffer` | `0x0008` | Discard the previous contents of the entire buffer.
`QOpenGLBuffer::RangeFlushExplicit` | `0x0010` | Indicates that modifications are to be flushed explicitly via `glFlushMappedBufferRange`.
`QOpenGLBuffer::RangeUnsynchronized` | `0x0020` | Indicates that pending operations should not be synchronized before returning from mapRange().

The RangeAccessFlags type is a typedef for QFlags<RangeAccessFlag>. It stores an OR combination of RangeAccessFlag values.

### enum QOpenGLBuffer::Type

This enum defines the type of OpenGL buffer object to create with QOpenGLBuffer.

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

### enum QOpenGLBuffer::UsagePattern

This enum defines the usage pattern of a QOpenGLBuffer object.

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

## Member Function Documentation

### QOpenGLBuffer::QOpenGLBuffer(const QOpenGLBuffer &other)

Constructs a shallow copy of other.

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

### QOpenGLBuffer::QOpenGLBuffer(QOpenGLBuffer::Type type)

Constructs a new buffer object of type.

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

See also create().

### QOpenGLBuffer::QOpenGLBuffer()

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

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

See also create().

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

Assigns a shallow copy of other to this object.

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

### QOpenGLBuffer::~QOpenGLBuffer()

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

### void QOpenGLBuffer::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 QOpenGLBuffer::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 QOpenGLBuffer::bind()

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

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

See also release() and create().

### GLuint QOpenGLBuffer::bufferId() const

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

See also isCreated().

### bool QOpenGLBuffer::create()

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

This function must be called with a current QOpenGLContext. 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 OpenGL implementation does not support buffers, or there is no current QOpenGLContext.

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

### void QOpenGLBuffer::destroy()

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

### bool QOpenGLBuffer::isCreated() const

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

See also create() and destroy().

### void *QOpenGLBuffer::map(QOpenGLBuffer::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.

Note: This function is only supported under OpenGL ES 2.0 or earlier if the `GL_OES_mapbuffer` extension is present.

Note: On OpenGL ES 3.0 and newer, or, in case if desktop OpenGL, if `GL_ARB_map_buffer_range` is supported, this function uses `glMapBufferRange` instead of `glMapBuffer`.

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

### void *QOpenGLBuffer::mapRange(int offset, int count, QOpenGLBuffer::RangeAccessFlags access)

Maps the range specified by offset and count of 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 specifies a combination of access flags.

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

Note: This function is not available on OpenGL ES 2.0 and earlier.

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

### bool QOpenGLBuffer::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 QOpenGLBuffer::release()

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

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

See also bind().

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

Releases the buffer associated with type in the current QOpenGLContext.

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

     QOpenGLBuffer::release(QOpenGLBuffer::VertexBuffer);

### void QOpenGLBuffer::setUsagePattern(QOpenGLBuffer::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 QOpenGLBuffer::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().

### QOpenGLBuffer::Type QOpenGLBuffer::type() const

Returns the type of buffer represented by this object.

### bool QOpenGLBuffer::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().

Note: This function is only supported under OpenGL ES 2.0 and earlier if the `GL_OES_mapbuffer` extension is present.

See also map().

### QOpenGLBuffer::UsagePattern QOpenGLBuffer::usagePattern() const

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

See also setUsagePattern().

### void QOpenGLBuffer::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().