Contents

• Public Types
• Public Functions
• Static Public Members
• Related Non-Members
• Detailed Description

Detailed Description

TheQPlatformWindowFormat class specifies the display format of anOpenGL rendering context and if possible attributes of the corresponding QPlatformWindow.

QWidget has a setter and getter function forQPlatformWindowFormat. These functions can be used by the application programmer to signal what kind of format he wants to the window and glcontext should have. However, it is not always possible to fulfill these requirements. The application programmer should therefore check the resultingQPlatformWindowFormat from QPlatformGLContext to see the format that was actually created.

A display format has several characteristics:

• Double or single buffering.
• Depth buffer.
• RGBA or color index mode.
• Alpha channel.
• Accumulation buffer.
• Stencil buffer.
• Stereo buffers.
• Direct rendering.
• Multisample buffers.

You can also specify preferred bit depths for the color buffer, depth buffer, alpha buffer, accumulation buffer and the stencil buffer with the functions:setRedBufferSize(),setGreenBufferSize(),setBlueBufferSize(),setDepthBufferSize(),setAlphaBufferSize(),setAccumBufferSize() andsetStencilBufferSize().

Note that even if you specify that you prefer a 32 bit depth buffer (e.g. withsetDepthBufferSize(32)), the format that is chosen may not have a 32 bit depth buffer, even if there is a format available with a 32 bit depth buffer. The main reason for this is how the system dependant picking algorithms work on the different platforms, and some format options may have higher precedence than others.

You create and tell aQPlatformWindowFormat object what rendering options you want from anOpenGL rendering context.

OpenGL drivers or accelerated hardware may or may not support advanced features such as alpha channel or stereographic viewing. If you request some features that the driver/hardware does not provide when you create aQGLWidget, you will get a rendering context with the nearest subset of features.

There are different ways to define the display characteristics of a rendering context. One is to create aQPlatformWindowFormat and make it the default for the entire application:

QGLFormat fmt;fmt.setAlpha(true);fmt.setStereo(true);QGLFormat::setDefaultFormat(fmt);

Or you can specify the desired format when creating an object of yourQGLWidget subclass:

QGLFormat fmt;fmt.setDoubleBuffer(false);// single bufferfmt.setDirectRendering(false);// software renderingMyGLWidget* myWidget=new MyGLWidget(fmt,...);

After the widget has been created, you can find out which of the requested features the system was able to provide:

QGLFormat fmt;fmt.setOverlay(true);fmt.setStereo(true);MyGLWidget* myWidget=new MyGLWidget(fmt,...);if (!myWidget->format().stereo()) {// ok, goggles offif (!myWidget->format().hasOverlay()) {qFatal("Cool hardware required");    }}

Member Type Documentation

enum QPlatformWindowFormat::FormatOption
flags QPlatformWindowFormat::FormatOptions

The FormatOptions type is a typedef forQFlags<FormatOption>. It stores an OR combination of FormatOption values.

enum QPlatformWindowFormat::WindowApi

Member Function Documentation

QPlatformWindowFormat::QPlatformWindowFormat()

Constructs aQPlatformWindowFormat object with the following default settings:

• Double buffer: Enabled.
• Depth buffer: Enabled.
• RGBA: Enabled (i.e., color index disabled).
• Alpha channel: Disabled.
• Accumulator buffer: Disabled.
• Stencil buffer: Enabled.
• Stereo: Disabled.
• Direct rendering: Enabled.
• Multisample buffers: Disabled.

QPlatformWindowFormat::QPlatformWindowFormat(FormatOptions options)

Creates aQPlatformWindowFormat object that is a copy of the currentdefaultFormat().

Ifoptions is not 0, the default format is modified by the specified format options. Theoptions parameter should beQGL::FormatOption values OR'ed together.

This constructor makes it easy to specify a certain desired format in classes derived fromQGLWidget, for example:

// The rendering in MyGLWidget depends on using// stencil buffer and alpha channelMyGLWidget::MyGLWidget(QWidget* parent)    :QGLWidget(QGLFormat(QGL::StencilBuffer| QGL::AlphaChannel), parent){if (!format().stencil())qWarning("Could not get stencil buffer; results will be suboptimal");if (!format().alpha())qWarning("Could not get alpha channel; results will be suboptimal");...}

Note that there areQGL::FormatOption values to turn format settings both on and off; e.g.,QGL::DepthBuffer andQGL::NoDepthBuffer,QGL::DirectRendering andQGL::IndirectRendering, etc.

See alsodefaultFormat() andsetOption().

QPlatformWindowFormat::QPlatformWindowFormat(constQPlatformWindowFormat & other)

Constructs a copy ofother.

QPlatformWindowFormat::~QPlatformWindowFormat()

Destroys theQPlatformWindowFormat.

bool QPlatformWindowFormat::accum() const

Returns true if the accumulation buffer is enabled; otherwise returns false. The accumulation buffer is disabled by default.

See alsosetAccum() andsetAccumBufferSize().

int QPlatformWindowFormat::accumBufferSize() const

Returns the accumulation buffer size.

See alsosetAccumBufferSize(),accum(), andsetAccum().

bool QPlatformWindowFormat::alpha() const

Returns true if the alpha buffer in the framebuffer is enabled; otherwise returns false. The alpha buffer is disabled by default.

See alsosetAlpha() andsetAlphaBufferSize().

int QPlatformWindowFormat::alphaBufferSize() const

Returns the alpha buffer size.

See alsoalpha(),setAlpha(), andsetAlphaBufferSize().

int QPlatformWindowFormat::blueBufferSize() const

Returns the blue buffer size.

This function was introduced in Qt 4.2.

See alsosetBlueBufferSize().

[static]QPlatformWindowFormat QPlatformWindowFormat::defaultFormat()

Returns the defaultQPlatformWindowFormat for the application. AllQGLWidget objects that are created use this format unless another format is specified, e.g. when they are constructed.

If no special default format has been set usingsetDefaultFormat(), the default format is the same as that created withQPlatformWindowFormat().

See alsosetDefaultFormat().

bool QPlatformWindowFormat::depth() const

Returns true if the depth buffer is enabled; otherwise returns false. The depth buffer is enabled by default.

See alsosetDepth() andsetDepthBufferSize().

int QPlatformWindowFormat::depthBufferSize() const

Returns the depth buffer size.

See alsodepth(),setDepth(), andsetDepthBufferSize().

bool QPlatformWindowFormat::directRendering() const

Returns true if direct rendering is enabled; otherwise returns false.

Direct rendering is enabled by default.

See alsosetDirectRendering().

bool QPlatformWindowFormat::doubleBuffer() const

Returns true if double buffering is enabled; otherwise returns false. Double buffering is enabled by default.

See alsosetDoubleBuffer().

int QPlatformWindowFormat::greenBufferSize() const

Returns the green buffer size.

This function was introduced in Qt 4.2.

See alsosetGreenBufferSize().

bool QPlatformWindowFormat::hasWindowSurface() const

Returns true if the corresponding widget has an instance of QWindowSurface.

Otherwise returns false.

WindowSurface is enabled by default.

int QPlatformWindowFormat::redBufferSize() const

Returns the red buffer size.

This function was introduced in Qt 4.2.

See alsosetRedBufferSize().

bool QPlatformWindowFormat::rgba() const

Returns true if RGBA color mode is set. Returns false if color index mode is set. The default color mode is RGBA.

See alsosetRgba().

bool QPlatformWindowFormat::sampleBuffers() const

Returns true if multisample buffer support is enabled; otherwise returns false.

The multisample buffer is disabled by default.

See alsosetSampleBuffers().

int QPlatformWindowFormat::samples() const

Returns the number of samples per pixel when multisampling is enabled. By default, the highest number of samples that is available is used.

See alsosetSampleBuffers(),sampleBuffers(), andsetSamples().

void QPlatformWindowFormat::setAccum(bool enable)

Ifenable is true enables the accumulation buffer; otherwise disables the accumulation buffer.

The accumulation buffer is disabled by default.

The accumulation buffer is used to create blur effects and multiple exposures.

See alsoaccum() andsetAccumBufferSize().

void QPlatformWindowFormat::setAccumBufferSize(int size)

Set the preferred accumulation buffer size, wheresize is the bit depth for each RGBA component.

See alsoaccum(),setAccum(), andaccumBufferSize().

void QPlatformWindowFormat::setAlpha(bool enable)

Ifenable is true enables the alpha buffer; otherwise disables the alpha buffer.

The alpha buffer is disabled by default.

The alpha buffer is typically used for implementing transparency or translucency. The A in RGBA specifies the transparency of a pixel.

See alsoalpha() andsetAlphaBufferSize().

void QPlatformWindowFormat::setAlphaBufferSize(int size)

Set the preferred alpha buffer size tosize. This function implicitly enables the alpha channel.

See alsosetRedBufferSize(),setGreenBufferSize(), andalphaBufferSize().

void QPlatformWindowFormat::setBlueBufferSize(int size)

Set the preferred blue buffer size tosize.

This function was introduced in Qt 4.2.

See alsoblueBufferSize(),setRedBufferSize(),setGreenBufferSize(), andsetAlphaBufferSize().

[static]void QPlatformWindowFormat::setDefaultFormat(constQPlatformWindowFormat & f)

Sets a new defaultQPlatformWindowFormat for the application tof. For example, to set single buffering as the default instead of double buffering, your main() might contain code like this:

QApplication a(argc, argv);QGLFormat f;f.setDoubleBuffer(false);QGLFormat::setDefaultFormat(f);

See alsodefaultFormat().

void QPlatformWindowFormat::setDepth(bool enable)

Ifenable is true enables the depth buffer; otherwise disables the depth buffer.

The depth buffer is enabled by default.

The purpose of a depth buffer (or Z-buffering) is to remove hidden surfaces. Pixels are assigned Z values based on the distance to the viewer. A pixel with a high Z value is closer to the viewer than a pixel with a low Z value. This information is used to decide whether to draw a pixel or not.

See alsodepth() andsetDepthBufferSize().

void QPlatformWindowFormat::setDepthBufferSize(int size)

Set the minimum depth buffer size tosize.

See alsodepthBufferSize(),setDepth(), anddepth().

void QPlatformWindowFormat::setDirectRendering(bool enable)

Ifenable is true enables direct rendering; otherwise disables direct rendering.

Direct rendering is enabled by default.

Enabling this option will makeOpenGL bypass the underlying window system and render directly from hardware to the screen, if this is supported by the system.

See alsodirectRendering().

void QPlatformWindowFormat::setDoubleBuffer(bool enable)

Ifenable is true sets double buffering; otherwise sets single buffering.

Double buffering is enabled by default.

Double buffering is a technique where graphics are rendered on an off-screen buffer and not directly to the screen. When the drawing has been completed, the program calls a swapBuffers() function to exchange the screen contents with the buffer. The result is flicker-free drawing and often better performance.

See alsodoubleBuffer(),QGLContext::swapBuffers(), andQGLWidget::swapBuffers().

void QPlatformWindowFormat::setGreenBufferSize(int size)

Set the preferred green buffer size tosize.

This function was introduced in Qt 4.2.

See alsogreenBufferSize(),setRedBufferSize(),setBlueBufferSize(), andsetAlphaBufferSize().

void QPlatformWindowFormat::setOption(QPlatformWindowFormat::FormatOptions opt)

Sets the format option toopt.

See alsotestOption().

void QPlatformWindowFormat::setRedBufferSize(int size)

Set the preferred red buffer size tosize.

This function was introduced in Qt 4.2.

See alsoredBufferSize(),setGreenBufferSize(),setBlueBufferSize(), andsetAlphaBufferSize().

void QPlatformWindowFormat::setRgba(bool enable)

Ifenable is true sets RGBA mode. Ifenable is false sets color index mode.

The default color mode is RGBA.

RGBA is the preferred mode for mostOpenGL applications. In RGBA color mode you specify colors as red + green + blue + alpha quadruplets.

In color index mode you specify an index into a color lookup table.

See alsorgba().

void QPlatformWindowFormat::setSampleBuffers(bool enable)

Ifenable is true, a GL context with multisample buffer support is picked; otherwise ignored.

See alsosampleBuffers(),setSamples(), andsamples().

void QPlatformWindowFormat::setSamples(int numSamples)

Set the preferred number of samples per pixel when multisampling is enabled tonumSamples. By default, the highest number of samples available is used.

See alsosetSampleBuffers(),sampleBuffers(), andsamples().

void QPlatformWindowFormat::setSharedContext(QPlatformGLContext * context)

void QPlatformWindowFormat::setStencil(bool enable)

Ifenable is true enables the stencil buffer; otherwise disables the stencil buffer.

The stencil buffer is enabled by default.

The stencil buffer masks certain parts of the drawing area so that masked parts are not drawn on.

See alsostencil() andsetStencilBufferSize().

void QPlatformWindowFormat::setStencilBufferSize(int size)

Set the preferred stencil buffer size tosize.

See alsostencilBufferSize(),setStencil(), andstencil().

void QPlatformWindowFormat::setStereo(bool enable)

Ifenable is true enables stereo buffering; otherwise disables stereo buffering.

Stereo buffering is disabled by default.

Stereo buffering provides extra color buffers to generate left-eye and right-eye images.

See alsostereo().

void QPlatformWindowFormat::setSwapInterval(int interval)

Set the preferred swap interval. This can be used to sync the GL drawing into a system window to the vertical refresh of the screen. Setting aninterval value of 0 will turn the vertical refresh syncing off, any value higher than 0 will turn the vertical syncing on.

Under Windows and under X11, where theWGL_EXT_swap_control andGLX_SGI_video_sync extensions are used, theinterval parameter can be used to set the minimum number of video frames that are displayed before a buffer swap will occur. In effect, setting theinterval to 10, means there will be 10 vertical retraces between every buffer swap.

Under Windows theWGL_EXT_swap_control extension has to be present, and under X11 theGLX_SGI_video_sync extension has to be present.

This function was introduced in Qt 4.2.

See alsoswapInterval().

void QPlatformWindowFormat::setWindowApi(QPlatformWindowFormat::WindowApi api)

See alsowindowApi().

void QPlatformWindowFormat::setWindowSurface(bool enable)

Ifenable is true a top levelQWidget will create a QWindowSurface at creation;

otherwise theQWidget will only have a QPlatformWindow.

This is useful forQGLWidget where the QPlatformGLContext controls the surface.

See alsohasWindowSurface().

QPlatformGLContext * QPlatformWindowFormat::sharedGLContext() const

bool QPlatformWindowFormat::stencil() const

Returns true if the stencil buffer is enabled; otherwise returns false. The stencil buffer is enabled by default.

See alsosetStencil() andsetStencilBufferSize().

int QPlatformWindowFormat::stencilBufferSize() const

Returns the stencil buffer size.

See alsostencil(),setStencil(), andsetStencilBufferSize().

bool QPlatformWindowFormat::stereo() const

Returns true if stereo buffering is enabled; otherwise returns false. Stereo buffering is disabled by default.

See alsosetStereo().

int QPlatformWindowFormat::swapInterval() const

Returns the currently set swap interval. -1 is returned if setting the swap interval isn't supported in the system GL implementation.

This function was introduced in Qt 4.2.

See alsosetSwapInterval().

bool QPlatformWindowFormat::testOption(QPlatformWindowFormat::FormatOptions opt) const

Returns true if format optionopt is set; otherwise returns false.

See alsosetOption().

WindowApi QPlatformWindowFormat::windowApi() const

See alsosetWindowApi().

QPlatformWindowFormat & QPlatformWindowFormat::operator=(constQPlatformWindowFormat & other)

Assignsother to this object.

Related Non-Members

booloperator!=(constQPlatformWindowFormat & a, constQPlatformWindowFormat & b)

Returns false if all the options of the twoQPlatformWindowFormat objectsa andb are equal; otherwise returns true.

This function was introduced in Qt 4.8.

booloperator==(constQPlatformWindowFormat & a, constQPlatformWindowFormat & b)

Returns true if all the options of the twoQPlatformWindowFormat objectsa andb are equal; otherwise returns false.

This function was introduced in Qt 4.8.