Qt 5.6 | Qt GUI | C++ Classes | QPlatformGraphicsBuffer

Qt 5.6.2 Reference Documentation

# QPlatformGraphicsBuffer Class

The QPlatformGraphicsBuffer is a windowsystem abstraction for native graphics buffers More...

Header: | #include <QPlatformGraphicsBuffer>
qmake: | QT += gui
Since: | Qt 5.5

- List of all members, including inherited members

## Public Types

enum | AccessType { None, SWReadAccess, SWWriteAccess, TextureAccess, HWCompositor }
flags | AccessTypes
enum | Origin { OriginTopLeft, OriginBottomLeft }

## Public Functions

virtual | ~QPlatformGraphicsBuffer()
virtual bool | bindToTexture(const QRect &rect = QRect()) const
int | byteCount() const
virtual int | bytesPerLine() const
virtual const uchar * | data() const
virtual uchar * | data()
QPixelFormat | format() const
AccessTypes | isLocked() const
bool | lock(AccessTypes access, const QRect &rect = QRect())
virtual Origin | origin() const
QSize | size() const
void | unlock()

## Signals

void | unlocked(AccessTypes previousAccessTypes)

## Protected Functions

| QPlatformGraphicsBuffer(const QSize &size, const QPixelFormat &format)
virtual bool | doLock(AccessTypes access, const QRect &rect = QRect()) = 0
virtual void | doUnlock() = 0

## Detailed Description

The QPlatformGraphicsBuffer is a windowsystem abstraction for native graphics buffers

Different platforms have different ways of representing graphics buffers. On some platforms, it is possible to create one graphics buffer that you can bind to a texture and also get main memory access to the image bits. On the other hand, on some platforms all graphics buffer abstraction is completely hidden.

QPlatformGraphicsBuffer is an abstraction of a single Graphics Buffer.

There is no public constructor nor any public factory function.

QPlatformGraphicsBuffer is intended to be created by using platform specific APIs available from QtPlatformHeaders, or there might be accessor functions similar to the accessor function that QPlatformBackingstore has.

## Member Type Documentation

### enum QPlatformGraphicsBuffer::AccessType
flags QPlatformGraphicsBuffer::AccessTypes

This enum describes the access that is desired or granted for the graphics buffer.

Constant | Value
--- | ---
`QPlatformGraphicsBuffer::None` | `0x00`
`QPlatformGraphicsBuffer::SWReadAccess` | `0x01`
`QPlatformGraphicsBuffer::SWWriteAccess` | `0x02`
`QPlatformGraphicsBuffer::TextureAccess` | `0x04`
`QPlatformGraphicsBuffer::HWCompositor` | `0x08`

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

### enum QPlatformGraphicsBuffer::Origin

This enum describes the origin of the content of the buffer.

Constant | Value
--- | ---
`QPlatformGraphicsBuffer::OriginTopLeft` | `1`
`QPlatformGraphicsBuffer::OriginBottomLeft` | `0`

## Member Function Documentation

### `[protected]` QPlatformGraphicsBuffer::QPlatformGraphicsBuffer(const QSize &size, const QPixelFormat &format)

Protected constructor to initialize the private members.

size is the size of the buffer. format is the format of the buffer.

See also size() and format().

### `[virtual]` QPlatformGraphicsBuffer::~QPlatformGraphicsBuffer()

Virtual destructor.

### `[virtual]` bool QPlatformGraphicsBuffer::bindToTexture(const QRect &rect = QRect()) const

Binds the content of this graphics buffer into the currently bound texture.

This function should fail for buffers not capable of locking to TextureAccess.

rect is the subrect which is desired to be bounded to the texture. This argument has a no less than semantic, meaning more (if not all) of the buffer can be bounded to the texture. An empty QRect is interpreted as entire buffer should be bound.

This function only supports binding buffers to the GL_TEXTURE_2D texture target.

Returns true on success, otherwise false.

### int QPlatformGraphicsBuffer::byteCount() const

Accessor for the length of the data buffer. This function is a convenience function multiplying height of buffer with bytesPerLine().

See also data(), bytesPerLine(), and size().

### `[virtual]` int QPlatformGraphicsBuffer::bytesPerLine() const

Accessor for bytes per line in the graphics buffer.

### `[virtual]` const uchar *QPlatformGraphicsBuffer::data() const

Accessor for the bytes of the buffer. This function needs to be called on a buffer with SWReadAccess access lock. Behavior is undefined for modifying the memory returned when not having a SWWriteAccess.

### `[virtual]` uchar *QPlatformGraphicsBuffer::data()

Accessor for the bytes of the buffer. This function needs to be called on a buffer with SWReadAccess access lock. Behavior is undefined for modifying the memory returned when not having a SWWriteAccess.

### `[pure virtual protected]` bool QPlatformGraphicsBuffer::doLock(AccessTypes access, const QRect &rect = QRect())

This function should be reimplemented by subclasses. If one of the access types specified can not be locked, then all should fail and this function should return false.

rect is the subrect which is desired to be locked. This argument has a no less than semantic, meaning more (if not all) of the buffer can be locked. An empty QRect should be interpreted as the entire buffer should be locked.

It is safe to call isLocked() to verify the current lock state.

### `[pure virtual protected]` void QPlatformGraphicsBuffer::doUnlock()

This function should remove all locks set on the buffer.

It is safe to call isLocked() to verify the current lock state.

### QPixelFormat QPlatformGraphicsBuffer::format() const

Accessor for the pixel format of the buffer.

### AccessTypes QPlatformGraphicsBuffer::isLocked() const

Function to check if the buffer is locked.

See also lock().

### bool QPlatformGraphicsBuffer::lock(AccessTypes access, const QRect &rect = QRect())

Before the data can be retrieved or before a buffer can be bound to a texture it needs to be locked. This is a separate function call since this operation might be time consuming, and it would not be satisfactory to do it per function call.

access is the access type wanted.

rect is the subrect which is desired to be locked. This argument has a no less than semantic, meaning more (if not all) of the buffer can be locked. An empty QRect is interpreted as entire buffer should be locked.

Return true on successfully locking all AccessTypes specified access otherwise returns false and no locks have been granted.

### `[virtual]` Origin QPlatformGraphicsBuffer::origin() const

In origin of the content of the graphics buffer.

Default implementation is OriginTopLeft, as this is the coordinate system default for Qt. However, for most regular OpenGL textures this will be OriginBottomLeft.

### QSize QPlatformGraphicsBuffer::size() const

Accessor for content size.

### void QPlatformGraphicsBuffer::unlock()

Unlocks the current buffer lock.

This function calls doUnlock, and then emits the unlocked signal with the AccessTypes from before doUnlock was called.

### `[signal]` void QPlatformGraphicsBuffer::unlocked(AccessTypes previousAccessTypes)

Signal that is emitted after unlocked has been called.

previousAccessTypes is the access types locked before unlock was called.