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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QGLContext Class Reference<br><small>[<a href="opengl.html">OpenGL module</a>]</small></h1>
<p>The QGLContext class encapsulates an OpenGL rendering context.
<a href="#details">More...</a>
<p><tt>#include <<a href="qgl-h.html">qgl.h</a>></tt>
<p>Inherits <a href="qgl.html">QGL</a>.
<p><a href="qglcontext-members.html">List of all member functions.</a>
<h2>Public Members</h2>
<ul>
<li class=fn><a href="#QGLContext"><b>QGLContext</b></a> ( const QGLFormat & format, QPaintDevice * device )</li>
<li class=fn>virtual <a href="#~QGLContext"><b>~QGLContext</b></a> ()</li>
<li class=fn>virtual bool <a href="#create"><b>create</b></a> ( const QGLContext * shareContext = 0 )</li>
<li class=fn>bool <a href="#isValid"><b>isValid</b></a> () const</li>
<li class=fn>bool <a href="#isSharing"><b>isSharing</b></a> () const</li>
<li class=fn>virtual void <a href="#reset"><b>reset</b></a> ()</li>
<li class=fn>QGLFormat <a href="#format"><b>format</b></a> () const</li>
<li class=fn>QGLFormat <a href="#requestedFormat"><b>requestedFormat</b></a> () const</li>
<li class=fn>virtual void <a href="#setFormat"><b>setFormat</b></a> ( const QGLFormat & format )</li>
<li class=fn>virtual void <a href="#makeCurrent"><b>makeCurrent</b></a> ()</li>
<li class=fn>virtual void <a href="#swapBuffers"><b>swapBuffers</b></a> () const</li>
<li class=fn>QPaintDevice * <a href="#device"><b>device</b></a> () const</li>
<li class=fn>QColor <a href="#overlayTransparentColor"><b>overlayTransparentColor</b></a> () const</li>
</ul>
<h2>Static Public Members</h2>
<ul>
<li class=fn>const QGLContext * <a href="#currentContext"><b>currentContext</b></a> ()</li>
</ul>
<h2>Protected Members</h2>
<ul>
<li class=fn>virtual bool <a href="#chooseContext"><b>chooseContext</b></a> ( const QGLContext * shareContext = 0 )</li>
<li class=fn>virtual void <a href="#doneCurrent"><b>doneCurrent</b></a> ()</li>
<li class=fn>virtual int <a href="#choosePixelFormat"><b>choosePixelFormat</b></a> ( void * dummyPfd, HDC pdc )</li>
<li class=fn>virtual void * <a href="#chooseVisual"><b>chooseVisual</b></a> ()</li>
<li class=fn>virtual void * <a href="#chooseMacVisual"><b>chooseMacVisual</b></a> ( GDHandle device )</li>
<li class=fn>bool <a href="#deviceIsPixmap"><b>deviceIsPixmap</b></a> () const</li>
<li class=fn>bool <a href="#windowCreated"><b>windowCreated</b></a> () const</li>
<li class=fn>void <a href="#setWindowCreated"><b>setWindowCreated</b></a> ( bool on )</li>
<li class=fn>bool <a href="#initialized"><b>initialized</b></a> () const</li>
<li class=fn>void <a href="#setInitialized"><b>setInitialized</b></a> ( bool on )</li>
<li class=fn>void <a href="#generateFontDisplayLists"><b>generateFontDisplayLists</b></a> ( const QFont & font, int listBase )</li>
</ul>
<hr><a name="details"></a><h2>Detailed Description</h2>
The QGLContext class encapsulates an OpenGL rendering context.
<p>
<p> An OpenGL<sup>*</sup> rendering context is a complete set of
OpenGL state variables.
<p> The context's <a href="qgl.html#FormatOption-enum">format</a> is set in the
constructor or later with <a href="#setFormat">setFormat</a>(). The format options that are
actually set are returned by <a href="#format">format</a>(); the options you asked for
are returned by <a href="#requestedFormat">requestedFormat</a>(). Note that after a QGLContext
object has been constructed, the actual OpenGL context must be
created by explicitly calling the <a href="#create">create()</a>
function. The <a href="#makeCurrent">makeCurrent</a>() function makes this context the
current rendering context. You can make <em>no</em> context current
using <a href="#doneCurrent">doneCurrent</a>(). The <a href="#reset">reset</a>() function will reset the context
and make it invalid.
<p> You can examine properties of the context with, e.g. <a href="#isValid">isValid</a>(),
<a href="#isSharing">isSharing</a>(), <a href="#initialized">initialized</a>(), <a href="#windowCreated">windowCreated</a>() and
<a href="#overlayTransparentColor">overlayTransparentColor</a>().
<p> If you're using double buffering you can swap the screen contents
with the off-screen buffer using <a href="#swapBuffers">swapBuffers</a>().
<p> Please note that QGLContext is not thread safe.
<p> <sup>*</sup> OpenGL is a trademark of Silicon Graphics, Inc. in the
United States and other countries.
<p> <p>See also <a href="graphics.html">Graphics Classes</a> and <a href="images.html">Image Processing Classes</a>.
<hr><h2>Member Function Documentation</h2>
<h3 class=fn><a name="QGLContext"></a>QGLContext::QGLContext ( const <a href="qglformat.html">QGLFormat</a> & format, <a href="qpaintdevice.html">QPaintDevice</a> * device )
</h3>
Constructs an OpenGL context for the paint device <em>device</em>, which
can be a widget or a pixmap. The <em>format</em> specifies several
display options for the context.
<p> If the underlying OpenGL/Window system cannot satisfy all the
features requested in <em>format</em>, the nearest subset of features
will be used. After creation, the <a href="#format">format</a>() method will return the
actual format obtained.
<p> Note that after a QGLContext object has been constructed, <a href="#create">create()</a> must be called explicitly to create
the actual OpenGL context. The context will be <a href="#isValid">invalid</a> if it was not possible to obtain a GL context at
all.
<p> <p>See also <a href="#format">format</a>() and <a href="#isValid">isValid</a>().
<h3 class=fn><a name="~QGLContext"></a>QGLContext::~QGLContext ()<tt> [virtual]</tt>
</h3>
Destroys the OpenGL context and frees its resources.
<h3 class=fn>bool <a name="chooseContext"></a>QGLContext::chooseContext ( const <a href="qglcontext.html">QGLContext</a> * shareContext = 0 )<tt> [virtual protected]</tt>
</h3>
<p> This semi-internal function is called by <a href="#create">create</a>(). It creates a
system-dependent OpenGL handle that matches the <a href="#format">format</a>() of <em>shareContext</em> as closely as possible.
<p> On Windows, it calls the virtual function <a href="#choosePixelFormat">choosePixelFormat</a>(),
which finds a matching pixel format identifier. On X11, it calls
the virtual function <a href="#chooseVisual">chooseVisual</a>() which finds an appropriate X
visual. On other platforms it may work differently.
<h3 class=fn>void * <a name="chooseMacVisual"></a>QGLContext::chooseMacVisual ( GDHandle device )<tt> [virtual protected]</tt>
</h3>
<p> <strong>Mac only</strong>: This virtual function tries to find a
visual that matches the format using the given <em>device</em> handle,
reducing the demands if the original request cannot be met.
<p> The algorithm for reducing the demands of the format is quite
simple-minded, so override this method in your subclass if your
application has specific requirements on visual selection.
<p> <p>See also <a href="#chooseContext">chooseContext</a>().
<h3 class=fn>int <a name="choosePixelFormat"></a>QGLContext::choosePixelFormat ( void * dummyPfd, HDC pdc )<tt> [virtual protected]</tt>
</h3>
<strong>Win32 only</strong> This virtual function chooses a pixel
format that matches the OpenGL <a href="#setFormat">format</a>.
Reimplement this function in a subclass if you need a custom
context.
<p> <b>Warning:</b> The <em>dummyPfd</em> pointer and <em>pdc</em> are used as a <tt>PIXELFORMATDESCRIPTOR*</tt>. We use <tt>void</tt> to avoid using
Windows-specific types in our header files.
<p> <p>See also <a href="#chooseContext">chooseContext</a>().
<h3 class=fn>void * <a name="chooseVisual"></a>QGLContext::chooseVisual ()<tt> [virtual protected]</tt>
</h3>
<strong>X11 only</strong>: This virtual function tries to find a
visual that matches the format, reducing the demands if the original
request cannot be met.
<p> The algorithm for reducing the demands of the format is quite
simple-minded, so override this method in your subclass if your
application has spcific requirements on visual selection.
<p> <p>See also <a href="#chooseContext">chooseContext</a>().
<h3 class=fn>bool <a name="create"></a>QGLContext::create ( const <a href="qglcontext.html">QGLContext</a> * shareContext = 0 )<tt> [virtual]</tt>
</h3>
Creates the GL context. Returns TRUE if it was successful in
creating a valid GL rendering context on the paint device
specified in the constructor; otherwise returns FALSE (i.e. the
context is invalid).
<p> After successful creation, <a href="#format">format</a>() returns the set of features of
the created GL rendering context.
<p> If <em>shareContext</em> points to a valid QGLContext, this method will
try to establish OpenGL display list sharing between this context
and the <em>shareContext</em>. Note that this may fail if the two
contexts have different formats. Use <a href="#isSharing">isSharing</a>() to see if sharing
succeeded.
<p> <b>Warning:</b> Implementation note: initialization of C++ class
members usually takes place in the class constructor. QGLContext
is an exception because it must be simple to customize. The
virtual functions <a href="#chooseContext">chooseContext</a>() (and <a href="#chooseVisual">chooseVisual</a>() for X11) can
be reimplemented in a subclass to select a particular context. The
problem is that virtual functions are not properly called during
construction (even though this is correct C++) because C++
constructs class hierarchies from the bottom up. For this reason
we need a <a href="#create">create</a>() function.
<p> <p>See also <a href="#chooseContext">chooseContext</a>(), <a href="#format">format</a>(), and <a href="#isValid">isValid</a>().
<h3 class=fn>const <a href="qglcontext.html">QGLContext</a> * <a name="currentContext"></a>QGLContext::currentContext ()<tt> [static]</tt>
</h3>
<p> Returns the current context, i.e. the context to which any OpenGL
commands will currently be directed. Returns 0 if no context is
current.
<p> <p>See also <a href="#makeCurrent">makeCurrent</a>().
<h3 class=fn><a href="qpaintdevice.html">QPaintDevice</a> * <a name="device"></a>QGLContext::device () const
</h3>
<p> Returns the paint device set for this context.
<p> <p>See also <a href="#QGLContext">QGLContext::QGLContext</a>().
<h3 class=fn>bool <a name="deviceIsPixmap"></a>QGLContext::deviceIsPixmap () const<tt> [protected]</tt>
</h3>
<p> Returns TRUE if the paint device of this context is a pixmap;
otherwise returns FALSE.
<h3 class=fn>void <a name="doneCurrent"></a>QGLContext::doneCurrent ()<tt> [virtual protected]</tt>
</h3>
<p> Makes no GL context the current context. Normally, you do not need
to call this function; QGLContext calls it as necessary.
<h3 class=fn><a href="qglformat.html">QGLFormat</a> <a name="format"></a>QGLContext::format () const
</h3>
<p> Returns the frame buffer format that was obtained (this may be a
subset of what was requested).
<p> <p>See also <a href="#requestedFormat">requestedFormat</a>().
<h3 class=fn>void <a name="generateFontDisplayLists"></a>QGLContext::generateFontDisplayLists ( const <a href="qfont.html">QFont</a> & font, int listBase )<tt> [protected]</tt>
</h3>
<p> Generates a set of 256 display lists for the 256 first characters
in the font <em>font</em>. The first list will start at index <em>listBase</em>.
<p> <p>See also <a href="qglwidget.html#renderText">QGLWidget::renderText</a>().
<h3 class=fn>bool <a name="initialized"></a>QGLContext::initialized () const<tt> [protected]</tt>
</h3>
<p> Returns TRUE if this context has been initialized, i.e. if
<a href="qglwidget.html#initializeGL">QGLWidget::initializeGL</a>() has been performed on it; otherwise
returns FALSE.
<p> <p>See also <a href="#setInitialized">setInitialized</a>().
<h3 class=fn>bool <a name="isSharing"></a>QGLContext::isSharing () const
</h3>
<p> Returns TRUE if display list sharing with another context was
requested in the <a href="#create">create</a>() call and the GL system was able to
fulfill this request; otherwise returns FALSE. Note that display
list sharing might not be supported between contexts with
different formats.
<h3 class=fn>bool <a name="isValid"></a>QGLContext::isValid () const
</h3>
<p> Returns TRUE if a GL rendering context has been successfully
created; otherwise returns FALSE.
<h3 class=fn>void <a name="makeCurrent"></a>QGLContext::makeCurrent ()<tt> [virtual]</tt>
</h3>
<p> Makes this context the current OpenGL rendering context. All GL
functions you call operate on this context until another context
is made current.
<p> In some very rare cases the underlying call may fail. If this
occurs an error message is output to stderr.
<h3 class=fn><a href="qcolor.html">QColor</a> <a name="overlayTransparentColor"></a>QGLContext::overlayTransparentColor () const
</h3>
<p> If this context is a valid context in an overlay plane, returns
the plane's transparent color. Otherwise returns an <a href="qcolor.html#isValid">invalid</a> color.
<p> The returned color's <a href="qcolor.html#pixel">pixel</a> value is
the index of the transparent color in the colormap of the overlay
plane. (Naturally, the color's RGB values are meaningless.)
<p> The returned <a href="qcolor.html">QColor</a> object will generally work as expected only
when passed as the argument to <a href="qglwidget.html#qglColor">QGLWidget::qglColor</a>() or
<a href="qglwidget.html#qglClearColor">QGLWidget::qglClearColor</a>(). Under certain circumstances it can
also be used to draw transparent graphics with a <a href="qpainter.html">QPainter</a>. See the
examples/opengl/overlay_x11 example for details.
<h3 class=fn><a href="qglformat.html">QGLFormat</a> <a name="requestedFormat"></a>QGLContext::requestedFormat () const
</h3>
<p> Returns the frame buffer format that was originally requested in
the constructor or <a href="#setFormat">setFormat</a>().
<p> <p>See also <a href="#format">format</a>().
<h3 class=fn>void <a name="reset"></a>QGLContext::reset ()<tt> [virtual]</tt>
</h3>
<p> Resets the context and makes it invalid.
<p> <p>See also <a href="#create">create</a>() and <a href="#isValid">isValid</a>().
<h3 class=fn>void <a name="setFormat"></a>QGLContext::setFormat ( const <a href="qglformat.html">QGLFormat</a> & format )<tt> [virtual]</tt>
</h3>
Sets a <em>format</em> for this context. The context is <a href="#reset">reset</a>.
<p> Call <a href="#create">create</a>() to create a new GL context that tries to match the
new format.
<p> <pre>
QGLContext *cx;
// ...
<a href="qglformat.html">QGLFormat</a> f;
f.<a href="qglformat.html#setStereo">setStereo</a>( TRUE );
cx-><a href="#setFormat">setFormat</a>( f );
if ( !cx-><a href="#create">create</a>() )
exit(); // no OpenGL support, or cannot render on the specified paintdevice
if ( !cx-><a href="#format">format</a>().stereo() )
exit(); // could not create stereo context
</pre>
<p> <p>See also <a href="#format">format</a>(), <a href="#reset">reset</a>(), and <a href="#create">create</a>().
<h3 class=fn>void <a name="setInitialized"></a>QGLContext::setInitialized ( bool on )<tt> [protected]</tt>
</h3>
<p> If <em>on</em> is TRUE the context has been initialized, i.e.
<a href="#setInitialized">QGLContext::setInitialized</a>() has been called on it. If <em>on</em> is
FALSE the context has not been initialized.
<p> <p>See also <a href="#initialized">initialized</a>().
<h3 class=fn>void <a name="setWindowCreated"></a>QGLContext::setWindowCreated ( bool on )<tt> [protected]</tt>
</h3>
<p> If <em>on</em> is TRUE the context has had a window created for it. If
<em>on</em> is FALSE no window has been created for the context.
<p> <p>See also <a href="#windowCreated">windowCreated</a>().
<h3 class=fn>void <a name="swapBuffers"></a>QGLContext::swapBuffers () const<tt> [virtual]</tt>
</h3>
<p> Swaps the screen contents with an off-screen buffer. Only works if
the context is in double buffer mode.
<p> <p>See also <a href="qglformat.html#setDoubleBuffer">QGLFormat::setDoubleBuffer</a>().
<h3 class=fn>bool <a name="windowCreated"></a>QGLContext::windowCreated () const<tt> [protected]</tt>
</h3>
<p> Returns TRUE if a window has been created for this context;
otherwise returns FALSE.
<p> <p>See also <a href="#setWindowCreated">setWindowCreated</a>().
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