QGLFormat(3qt)QGLFormat(3qt)NAME
QGLFormat - The display format of an OpenGL rendering
context
#include <qgl.h>
Inherits QGL.
Public Members
QGLFormat ()
QGLFormat ( int options, int plane = 0 )
bool doubleBuffer () const
void setDoubleBuffer ( bool enable )
bool depth () const
void setDepth ( bool enable )
bool rgba () const
void setRgba ( bool enable )
bool alpha () const
void setAlpha ( bool enable )
bool accum () const
void setAccum ( bool enable )
bool stencil () const
void setStencil ( bool enable )
bool stereo () const
void setStereo ( bool enable )
bool directRendering () const
void setDirectRendering ( bool enable )
bool hasOverlay () const
void setOverlay ( bool enable )
int plane () const
void setPlane ( int plane )
void setOption ( FormatOption opt )
bool testOption ( FormatOption opt ) const
Static Public Members
QGLFormat defaultFormat ()
void setDefaultFormat ( const QGLFormat & f )
QGLFormat defaultOverlayFormat ()
void setDefaultOverlayFormat ( const QGLFormat & f )
bool hasOpenGL ()
bool hasOpenGLOverlays ()
DESCRIPTION
The QGLFormat class specifies the display format of an
OpenGL rendering context.
A display format has several characteristics:
Double or single buffering.
Depth buffer.
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RGBA or color index mode.
Alpha channel.
Accumulation buffer.
Stencil buffer.
Stereo buffers.
Direct rendering.
Presence of an overlay.
The plane of an overlay format.
You create and tell a QGLFormat object what rendering
options you want from an OpenGL rendering context.
OpenGL drivers or accelerated hardware may or may not
support advanced features like alpha channel or
stereographic viewing. If you request some features the
driver/hardware does not provide when you create a
QGLWidget, you will get the a rendering context with the
nearest subset of features.
There are different ways of defining the display
characteristics of a rendering context. One is to create a
QGLFormat and make it default for the entire application:
QGLFormat f;
f.setAlpha( TRUE );
f.setStereo( TRUE );
QGLFormat::setDefaultFormat( f );
Or you can specify the desired format when creating an
object of your QGLWidget subclass:
QGLFormat f;
f.setDoubleBuffer( FALSE ); // I want single buffer
f.setDirectRendering( FALSE ); // I want software rendering
MyGLWidget* myWidget = new MyGLWidget( f, ... );
After the widget has been created, you can test which of
the requested features the system was able to provide:
QGLFormat f;
f.setOverlay( TRUE );
f.setStereo( TRUE );
MyGLWidget* myWidget = new MyGLWidget( f, ... );
if ( !w->format().stereo() ) {
// ok, goggles off
if ( !w->format().hasOverlay() ) {
qFatal( "Cool hardware wanted" );
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}
}
See also QGLContext and QGLWidget.
MEMBER FUNCTION DOCUMENTATIONQGLFormat::QGLFormat ()
Constructs a QGLFormat object with the factory default
settings:
Double buffer: Enabled.
Depth buffer: Enabled.
RGBA: Enabled (i.e. color index disabled).
Alpha channel: Disabled.
Accumulator buffer: Disabled.
Stencil buffer: Disabled.
Stereo: Disabled.
Direct rendering: Enabled.
Overlay: Disabled.
Plane: 0 (i.e. normal plane).
QGLFormat::QGLFormat ( int options, int plane = 0 )
Creates a QGLFormat object that is a copy of the current
application default format.
If options is not 0, this copy will be modified by these
format options. The options parameter must be FormatOption
values OR'ed together.
This constructor makes it easy to specify a certain
desired format in classes derived from QGLWidget, for
example:
// The rendering in MyGLWidget depends on using
// stencil buffer and alpha channel
MyGLWidget::MyGLWidget( QWidget* parent, const char* name )
: QGLWidget( QGLFormat( StencilBuffer | AlphaChannel ), parent, name )
{
if ( !format().stencil() )
qWarning( "Could not get stencil buffer; results will be suboptimal" );
if ( !format().alphaChannel() )
qWarning( "Could not get alpha channel; results will be suboptimal" );
...
}
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Note that there exists FormatOption values for both
turning on and off all format settings, e.g. DepthBuffer
and NoDepthBuffer, DirectRendering and IndirectRendering,
etc.
See also defaultFormat() and setOption().
bool QGLFormat::accum () const
Returns TRUE if the accumulation buffer is enabled,
otherwise FALSE. The accumulation buffer is disabled by
default.
See also setAccum().
bool QGLFormat::alpha () const
Returns TRUE if the alpha channel of the framebuffer is
enabled, otherwise FALSE. The alpha channel is disabled by
default.
See also setAlpha().
QGLFormat QGLFormat::defaultFormat () [static]
Returns the default QGLFormat for the application. All
QGLWidgets that are created use this format unless
anything else is specified.
If no special default format has been set using
setDefaultFormat(), the default format is the same as that
created with QGLFormat().
See also setDefaultFormat().
QGLFormat QGLFormat::defaultOverlayFormat () [static]
Returns the default QGLFormat for overlay contexts.
The factory default overlay format is:
Double buffer: Disabled.
Depth buffer: Disabled.
RGBA: Disabled (i.e. color index enabled).
Alpha channel: Disabled.
Accumulator buffer: Disabled.
Stencil buffer: Disabled.
Stereo: Disabled.
Direct rendering: Enabled.
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Overlay: Disabled.
Plane: 1 (i.e. first overlay plane).
See also setDefaultFormat().
bool QGLFormat::depth () const
Returns TRUE if the depth buffer is enabled, otherwise
FALSE. The depth buffer is enabled by default.
See also setDepth().
bool QGLFormat::directRendering () const
Returns TRUE if direct rendering is enabled, otherwise
FALSE.
Direct rendering is enabled by default.
See also setDirectRendering().
bool QGLFormat::doubleBuffer () const
Returns TRUE if double buffering is enabled, otherwise
FALSE. Double buffering is enabled by default.
See also setDoubleBuffer().
bool QGLFormat::hasOpenGL () [static]
Returns TRUE if the window system has any OpenGL support,
otherwise FALSE.
Note: This function may not be called until the
QApplication object has been created.
bool QGLFormat::hasOpenGLOverlays () [static]
Returns TRUE if the window system supports OpenGL
overlays, otherwise FALSE.
Note: This function may not be called until the
QApplication object has been created.
bool QGLFormat::hasOverlay () const
Returns TRUE if overlay plane is enabled, otherwise FALSE.
Overlay is disabled by default.
See also setOverlay().
int QGLFormat::plane () const
Returns the plane of this format. Default for normal
formats is 0, which means the normal plane; default for
overlay formats is 1, which is the first overlay plane.
See also setPlane().
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QGLFormat(3qt)QGLFormat(3qt)bool QGLFormat::rgba () const
Returns TRUE if RGBA color mode is set, or FALSE if color
index mode is set. The default color mode is RGBA.
See also setRgba().
void QGLFormat::setAccum ( bool enable )
Enables the accumulation buffer if enable is TRUE, or
disables it if enable is FALSE.
The accumulation buffer is disabled by default.
The accumulation buffer is used for create blur effects
and multiple exposures.
See also accum().
void QGLFormat::setAlpha ( bool enable )
Enables the alpha channel of the framebuffer if enable is
TRUE, or disables it if enable is FALSE.
The alpha buffer is disabled by default.
The alpha channel is typically used for implementing
transparency or translucency. The A in RGBA specifies the
transparency of a pixel.
See also alpha().
void QGLFormat::setDefaultFormat ( const QGLFormat & f ) [static]
Sets a new default QGLFormat for the application. For
example, to set single buffering as default instead of
double buffering, your main() can contain:
QApplication a(argc, argv);
QGLFormat f;
f.setDoubleBuffer( FALSE );
QGLFormat::setDefaultFormat( f );
See also defaultFormat().
void QGLFormat::setDefaultOverlayFormat ( const QGLFormat & f )
[static]
Sets a new default QGLFormat for overlay contexts. This
format is used whenever a QGLWidget is created with a
format with hasOverlay() enabled.
For example, to get a double buffered overlay contexts (if
available), the code can do:
QGLFormat f = QGLFormat::defaultOverlayFormat();
f.setDoubleBuffer( TRUE );
QGLFormat::setDefaultOverlayFormat( f );
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As usual, you can test after the widget creation whether
the underlying OpenGL system was able to provide the
requested specification:
// (...continued from above)
MyGLWidget* myWidget = new MyGLWidget( QGLFormat( QGL::HasOverlay ), ... );
if ( myWidget->format().hasOverlay() ) {
// Yes, we got an overlay, let's check _its_ format:
QGLContext* olContext = myWidget->overlayContext();
if ( olContext->format().doubleBuffer() )
; // yes, we got a double buffered overlay
else
; // no, only single buffered overlays were available
}
See also defaultOverlayFormat().
void QGLFormat::setDepth ( bool enable )
Enables the depth buffer if enable is TRUE, or disables it
if enable is FALSE.
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 also depth().
void QGLFormat::setDirectRendering ( bool enable )
Enables direct rendering if enable is TRUE, or disables it
if enable is FALSE.
Direct rendering is enabled by default.
Enabling this option will make OpenGL bypass the
underlying window system and render directly from hardware
to the screen, if this is supported by the system.
See also directRendering().
void QGLFormat::setDoubleBuffer ( bool enable )
Sets double buffering if enable is TRUE or single
buffering if enable is FALSE.
Double buffering is enabled by default.
Double buffering is a technique where graphics is rendered
to 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
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the buffer. The result is flicker-free drawing and often
better performance.
See also doubleBuffer(), QGLContext::swapBuffers() and
QGLWidget::swapBuffers().
void QGLFormat::setOption ( FormatOption opt )
Sets the option opt.
See also testOption().
void QGLFormat::setOverlay ( bool enable )
Enables an overlay plane if enable is TRUE; otherwise
disables it.
Enabling the overlay plane will cause QGLWidget to create
an additional context in an overlay plane. See the
QGLWidget documentation for further information.
See also hasOverlay().
void QGLFormat::setPlane ( int plane )
Sets the requested plane. 0 is the normal plane, 1 is the
first overlay plane, 2 is the second overlay plane, etc.,
and -1, -2, etc. are underlay planes.
Note that, in contrast to the other format specifications,
the plane specifications will be matched exactly. Thus, if
you specify a plane that the underlying OpenGL system
cannot provide, an invalid QGLWidget will be created.
See also plane().
void QGLFormat::setRgba ( bool enable )
Sets RGBA mode if enable is TRUE, or color index mode if
enable is FALSE.
The default color mode is RGBA.
RGBA is the preferred mode for most OpenGL applications.
In RGBA color mode you specify colors as a red + green +
blue + alpha quadruplet.
In color index mode you specify an index into a color
lookup table.
See also rgba().
void QGLFormat::setStencil ( bool enable )
Enables the stencil buffer if enable is TRUE, or disables
it if enable is FALSE.
The stencil buffer is disabled by default.
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The stencil buffer masks away drawing from certain parts
of the screen.
See also stencil().
void QGLFormat::setStereo ( bool enable )
Enables stereo buffering if enable is TRUE, or disables it
if enable is FALSE.
Stereo buffering is disabled by default.
Stereo buffering provides extra color buffers to generate
left-eye and right-eye images.
See also stereo().
bool QGLFormat::stencil () const
Returns TRUE if the stencil buffer is enabled, otherwise
FALSE. The stencil buffer is disabled by default.
See also setStencil().
bool QGLFormat::stereo () const
Returns TRUE if stereo buffering is enabled, otherwise
FALSE. Stereo buffering is disabled by default.
See also setStereo().
bool QGLFormat::testOption ( FormatOption opt ) const
Returns TRUE if format option opt is set, otherwise FALSE.
See also setOption().
SEE ALSO
http://doc.trolltech.com/qglformat.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
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