Qt 4.8: QDirectPainter Class Reference

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# QDirectPainter Class Reference

The QDirectPainter class provides direct access to the underlying hardware in Qt for Embedded Linux. More...

     #include <QDirectPainter>

Inherits: QObject.

- List of all members, including inherited members
- Obsolete members

## Public Types

enum | SurfaceFlag { NonReserved, Reserved, ReservedSynchronous }

## Public Functions

| QDirectPainter ( QObject * parent = 0, SurfaceFlag flag = NonReserved )
| ~QDirectPainter ()
QRegion | allocatedRegion () const
void | endPainting ()
void | endPainting ( const QRegion & region )
void | flush ( const QRegion & region )
QRect | geometry () const
void | lower ()
void | raise ()
virtual void | regionChanged ( const QRegion & newRegion )
QRegion | requestedRegion () const
void | setGeometry ( const QRect & rectangle )
void | setRegion ( const QRegion & region )
void | startPainting ( bool lockDisplay = true )
WId | winId () const

- 29 public functions inherited from QObject

## Static Public Members

uchar * | frameBuffer ()
int | linestep ()
void | lock ()
int | screenDepth ()
int | screenHeight ()
int | screenWidth ()
void | unlock ()

- 7 static public members inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 1 public slot inherited from QObject
- 1 signal inherited from QObject
- 8 protected functions inherited from QObject

## Detailed Description

The QDirectPainter class provides direct access to the underlying hardware in Qt for Embedded Linux.

Note that this class is only available in Qt for Embedded Linux.

QDirectPainter allows a client application to reserve a region of the framebuffer and render directly onto the screen. There are two ways of using the QDirectPainter class: You can either reserve a region using the provided static functions, or you can instantiate an object and make use of its more dynamic API.

### Dynamic Allocation

By instantiating a QDirectPainter object using the default QDirectPainter::NonReserved surface flag, the client application only gets some control over the reserved region, i.e., it can still render directly onto the screen but the allocated region may change (for example, if a window with a higher focus requests parts of the same region). The currently allocated region can be retrieved using the allocatedRegion() function, while the requestedRegion() function returns the originally reserved region.

### Static Allocation

Using the static approach, the client application gets complete control over the reserved region, i.e., the affected region will never be modified by the screen driver.

To create a static region, pass the QDirectPainter::Reserved surface flag to the constructor. After the reserved region is reported through regionChanged(), the allocated region will not change, unless setRegion() is called.

If QDirectPainter::ReservedSynchronous is passed to the constructor, calls to setRegion() will block until the region is reserved, meaning that allocatedRegion() will be available immediately. Note that in the current version setRegion() will cause the application event loop to be entered, potentially causing reentrancy issues.

### Rendering

To draw on a given region, the application must first get hold of a pointer to the framebuffer. In most cases, this pointer can be retrieved using the QDirectPainter::frameBuffer() function. But note that if the current screen has subscreens, you must query the screen driver instead to identify the correct subscreen. A pointer to the current screen driver can always be retrieved using the static QScreen::instance() function. Then use QScreen's subScreenIndexAt() and subScreens() functions to access the correct subscreen, and the subscreen's base() function to retrieve a pointer to the framebuffer.

Depending on the hardware, it might be necessary to lock the framebuffer for exclusive use while writing to it. This is possible using the lock() and unlock() functions. Note that calling lock() will prevent all other applications from working until unlock() is called.

In addition, QDirectPainter provides several functions returning information about the framebuffer: the linestep() function returns the length (in bytes) of each scanline of the framebuffer while the screenDepth(), screenWidth() and screenHeight() function return the screen metrics.

See also QScreen, QWSEmbedWidget, and Qt for Embedded Linux Architecture.

## Member Type Documentation

### enum QDirectPainter::SurfaceFlag

This enum describes the behavior of the region reserved by this QDirectPainter object.

Constant | Value | Description
--- | --- | ---
`QDirectPainter::NonReserved` | `0` | The allocated region may change, e.g., if a window with a higher focus requests parts of the same region. See also Dynamic Allocation.
`QDirectPainter::Reserved` | `1` | The allocated region will never change. See also Static Allocation.
`QDirectPainter::ReservedSynchronous` | `3` | The allocated region will never change and each function that changes the allocated region will be blocking.

See also allocatedRegion().

## Member Function Documentation

### QDirectPainter::QDirectPainter ( QObject * parent = 0, SurfaceFlag flag = NonReserved )

Constructs a QDirectPainter object with the given parent and surface flag.

### QDirectPainter::~QDirectPainter ()

Destroys this QDirectPainter object, releasing the reserved region.

See also allocatedRegion().

### QRegion QDirectPainter::allocatedRegion () const

Returns the currently reserved region.

Note that if the QDirectPainter::Reserved flag is set, the region returned by this function will always be equivalent to the region returned by the requestedRegion() function. Otherwise they might differ (see Dynamic Allocation for details).

This function was introduced in Qt 4.2.

See also requestedRegion() and geometry().

### void QDirectPainter::endPainting ()

Call this function when you are done updating the screen. It will notify the hardware, if necessary, that your painting operations have ended.

This function was introduced in Qt 4.2.

### void QDirectPainter::endPainting ( const QRegion & region )

This is an overloaded function.

This function will automatically call flush() to flush the region to the display before notifying the hardware, if necessary, that painting operations have ended.

This function was introduced in Qt 4.3.

### void QDirectPainter::flush ( const QRegion & region )

Flushes the region onto the screen.

This function was introduced in Qt 4.3.

### uchar * QDirectPainter::frameBuffer ()`[static]`

Returns a pointer to the beginning of the display memory.

Note that it is the application's responsibility to limit itself to modifying only the reserved region.

Do not use this pointer if the current screen has subscreens, query the screen driver instead: A pointer to the current screen driver can always be retrieved using the static QScreen::instance() function. Then use QScreen's subScreenIndexAt() and subScreens() functions to access the correct subscreen, and the subscreen's base() function to retrieve a pointer to the framebuffer.

See also requestedRegion(), allocatedRegion(), and linestep().

### QRect QDirectPainter::geometry () const

Returns the bounding rectangle of the requested region.

This function was introduced in Qt 4.2.

See also setGeometry() and requestedRegion().

### int QDirectPainter::linestep ()`[static]`

Returns the length (in bytes) of each scanline of the framebuffer.

See also frameBuffer().

### void QDirectPainter::lock ()`[static]`

Locks access to the framebuffer.

Note that calling this function will prevent all other applications from updating the display until unlock() is called.

See also unlock().

### void QDirectPainter::lower ()

Lowers the reserved region to the bottom of the widget stack.

After this call the reserved region will be visually behind (and therefore obscured by) any overlapping widgets.

This function was introduced in Qt 4.2.

See also raise() and requestedRegion().

### void QDirectPainter::raise ()

Raises the reserved region to the top of the widget stack.

After this call the reserved region will be visually in front of any overlapping widgets.

This function was introduced in Qt 4.2.

See also lower() and requestedRegion().

### void QDirectPainter::regionChanged ( const QRegion & newRegion )`[virtual]`

This function is called when the allocated region changes.

This function is not called for region changes that happen while the startPainting() function is executing.

Note that the given region, newRegion, is not guaranteed to be correct at the time you access the display. To prevent reentrancy problems you should always call startPainting() before updating the display and then use allocatedRegion() to retrieve the correct region.

This function was introduced in Qt 4.2.

See also allocatedRegion(), startPainting(), and Dynamic Allocation.

### QRegion QDirectPainter::requestedRegion () const

Returns the region requested by this QDirectPainter.

Note that if the QDirectPainter::Reserved flag is set, the region returned by this function will always be equivalent to the region returned by the allocatedRegion() function. Otherwise they might differ (see Dynamic Allocation for details).

This function was introduced in Qt 4.2.

See also geometry(), setRegion(), and allocatedRegion().

### int QDirectPainter::screenDepth ()`[static]`

Returns the bit depth of the display.

See also screenHeight() and screenWidth().

### int QDirectPainter::screenHeight ()`[static]`

Returns the height of the display in pixels.

See also screenWidth() and screenDepth().

### int QDirectPainter::screenWidth ()`[static]`

Returns the width of the display in pixels.

See also screenHeight() and screenDepth().

### void QDirectPainter::setGeometry ( const QRect & rectangle )

Request to reserve the given rectangle of the framebuffer.

Note that the actually allocated region might differ from the requested one, e.g., if the given region overlaps with the region of another QDirectPainter object.

This function was introduced in Qt 4.2.

See also geometry(), allocatedRegion(), and setRegion().

### void QDirectPainter::setRegion ( const QRegion & region )

Requests to reserve the given region of the framebuffer.

Note that the actually allocated region might differ from the requested one, e.g., if the given region overlaps with the region of another QDirectPainter object.

This function was introduced in Qt 4.2.

See also region(), requestedRegion(), allocatedRegion(), and Dynamic Allocation.

### void QDirectPainter::startPainting ( bool lockDisplay = true )

Call this function before you start updating the pixels in the allocated region. The hardware will be notified, if necessary, that you are about to start painting operations.

Set lockDisplay if you want startPainting() and endPainting() to lock() and unlock() the display automatically.

Note that for a NonReserved direct painter, you must call allocatedRegion() after calling this function, since the allocated region is only guaranteed to be correct after this function has returned.

The regionChanged() function will not be called between startPainting() and endPainting().

This function was introduced in Qt 4.2.

See also endPainting() and flush().

### void QDirectPainter::unlock ()`[static]`

Unlocks the lock on the framebuffer (set using the lock() function), allowing other applications to access the screen.

See also lock().

### WId QDirectPainter::winId () const

Returns the window system identifier of the widget.

This function was introduced in Qt 4.2.