1QGLContext(3qt) QGLContext(3qt)
2
6 QGLContext - Encapsulates an OpenGL rendering context
7
9 #include <qgl.h>
10 Inherits QGL.
12 Public Members
14 QGLContext ( const QGLFormat & format, QPaintDevice * device )
15 virtual ~QGLContext ()
16 virtual bool create ( const QGLContext * shareContext = 0 )
17 bool isValid () const
18 bool isSharing () const
19 virtual void reset ()
20 QGLFormat format () const
21 QGLFormat requestedFormat () const
22 virtual void setFormat ( const QGLFormat & format )
23 virtual void makeCurrent ()
24 virtual void swapBuffers () const
25 QPaintDevice * device () const
26 QColor overlayTransparentColor () const
27 Static Public Members
29 const QGLContext * currentContext ()
30 Protected Members
32 virtual bool chooseContext ( const QGLContext * shareContext = 0 )
33 virtual void doneCurrent ()
34 virtual int choosePixelFormat ( void * dummyPfd, HDC pdc )
35 virtual void * chooseVisual ()
36 virtual void * chooseMacVisual ( GDHandle device )
37 bool deviceIsPixmap () const
38 bool windowCreated () const
39 void setWindowCreated ( bool on )
40 bool initialized () const
41 void setInitialized ( bool on )
42 void generateFontDisplayLists ( const QFont & font, int listBase )
43
45 The QGLContext class encapsulates an OpenGL rendering context.
46 An OpenGL<sup>*</sup> rendering context is a complete set of OpenGL
48 state variables.
49 The context's format is set in the constructor or later with
51 setFormat(). The format options that are actually set are returned by
52 format(); the options you asked for are returned by requestedFormat().
53 Note that after a QGLContext object has been constructed, the actual
54 OpenGL context must be created by explicitly calling the create()
55 function. The makeCurrent() function makes this context the current
56 rendering context. You can make no context current using doneCurrent().
57 The reset() function will reset the context and make it invalid.
58 You can examine properties of the context with, e.g. isValid(),
60 isSharing(), initialized(), windowCreated() and
61 overlayTransparentColor().
62 If you're using double buffering you can swap the screen contents with
64 the off-screen buffer using swapBuffers().
65 Please note that QGLContext is not thread safe.
67 <sup>*</sup> OpenGL is a trademark of Silicon Graphics, Inc. in the
69 United States and other countries.
70 See also Graphics Classes and Image Processing Classes.
72
75 Constructs an OpenGL context for the paint device device, which can be
76 a widget or a pixmap. The format specifies several display options for
77 the context.
78 If the underlying OpenGL/Window system cannot satisfy all the features
80 requested in format, the nearest subset of features will be used. After
81 creation, the format() method will return the actual format obtained.
82 Note that after a QGLContext object has been constructed, create() must
84 be called explicitly to create the actual OpenGL context. The context
85 will be invalid if it was not possible to obtain a GL context at all.
86 See also format() and isValid().
88
90 Destroys the OpenGL context and frees its resources.
91
93 [virtual protected]
94 This semi-internal function is called by create(). It creates a system-
95 dependent OpenGL handle that matches the format() of shareContext as
96 closely as possible.
97 On Windows, it calls the virtual function choosePixelFormat(), which
99 finds a matching pixel format identifier. On X11, it calls the virtual
100 function chooseVisual() which finds an appropriate X visual. On other
101 platforms it may work differently.
102
104 Mac only: This virtual function tries to find a visual that matches the
105 format using the given device handle, reducing the demands if the
106 original request cannot be met.
107 The algorithm for reducing the demands of the format is quite simple-
109 minded, so override this method in your subclass if your application
110 has specific requirements on visual selection.
111 See also chooseContext().
113
115 protected]
116 Win32 only This virtual function chooses a pixel format that matches
117 the OpenGL format. Reimplement this function in a subclass if you need
118 a custom context.
119 Warning: The dummyPfd pointer and pdc are used as a
121 PIXELFORMATDESCRIPTOR*. We use void to avoid using Windows-specific
122 types in our header files.
123 See also chooseContext().
125
127 X11 only: This virtual function tries to find a visual that matches the
128 format, reducing the demands if the original request cannot be met.
129 The algorithm for reducing the demands of the format is quite simple-
131 minded, so override this method in your subclass if your application
132 has spcific requirements on visual selection.
133 See also chooseContext().
135
137 Creates the GL context. Returns TRUE if it was successful in creating a
138 valid GL rendering context on the paint device specified in the
139 constructor; otherwise returns FALSE (i.e. the context is invalid).
140 After successful creation, format() returns the set of features of the
142 created GL rendering context.
143 If shareContext points to a valid QGLContext, this method will try to
145 establish OpenGL display list sharing between this context and the
146 shareContext. Note that this may fail if the two contexts have
147 different formats. Use isSharing() to see if sharing succeeded.
148 Warning: Implementation note: initialization of C++ class members
150 usually takes place in the class constructor. QGLContext is an
151 exception because it must be simple to customize. The virtual functions
152 chooseContext() (and chooseVisual() for X11) can be reimplemented in a
153 subclass to select a particular context. The problem is that virtual
154 functions are not properly called during construction (even though this
155 is correct C++) because C++ constructs class hierarchies from the
156 bottom up. For this reason we need a create() function.
157 See also chooseContext(), format(), and isValid().
159
161 Returns the current context, i.e. the context to which any OpenGL
162 commands will currently be directed. Returns 0 if no context is
163 current.
164 See also makeCurrent().
166
168 Returns the paint device set for this context.
169 See also QGLContext::QGLContext().
171
173 Returns TRUE if the paint device of this context is a pixmap; otherwise
174 returns FALSE.
175
177 Makes no GL context the current context. Normally, you do not need to
178 call this function; QGLContext calls it as necessary.
179
181 Returns the frame buffer format that was obtained (this may be a subset
182 of what was requested).
183 See also requestedFormat().
185
187 [protected]
188 Generates a set of 256 display lists for the 256 first characters in
189 the font font. The first list will start at index listBase.
190 See also QGLWidget::renderText().
192
194 Returns TRUE if this context has been initialized, i.e. if
195 QGLWidget::initializeGL() has been performed on it; otherwise returns
196 FALSE.
197 See also setInitialized().
199
201 Returns TRUE if display list sharing with another context was requested
202 in the create() call and the GL system was able to fulfill this
203 request; otherwise returns FALSE. Note that display list sharing might
204 not be supported between contexts with different formats.
205
207 Returns TRUE if a GL rendering context has been successfully created;
208 otherwise returns FALSE.
209
211 Makes this context the current OpenGL rendering context. All GL
212 functions you call operate on this context until another context is
213 made current.
214 In some very rare cases the underlying call may fail. If this occurs an
216 error message is output to stderr.
217
219 If this context is a valid context in an overlay plane, returns the
220 plane's transparent color. Otherwise returns an invalid color.
221 The returned color's pixel value is the index of the transparent color
223 in the colormap of the overlay plane. (Naturally, the color's RGB
224 values are meaningless.)
225 The returned QColor object will generally work as expected only when
227 passed as the argument to QGLWidget::qglColor() or
228 QGLWidget::qglClearColor(). Under certain circumstances it can also be
229 used to draw transparent graphics with a QPainter. See the
230 examples/opengl/overlay_x11 example for details.
231
233 Returns the frame buffer format that was originally requested in the
234 constructor or setFormat().
235 See also format().
237
239 Resets the context and makes it invalid.
240 See also create() and isValid().
242
244 Sets a format for this context. The context is reset.
245 Call create() to create a new GL context that tries to match the new
247 format.
248 QGLContext *cx;
250 // ...
251 QGLFormat f;
252 f.setStereo( TRUE );
253 cx->setFormat( f );
254 if ( !cx->create() )
255 exit(); // no OpenGL support, or cannot render on the specified paintdevice
256 if ( !cx->format().stereo() )
257 exit(); // could not create stereo context
258 See also format(), reset(), and create().
260
262 If on is TRUE the context has been initialized, i.e.
263 QGLContext::setInitialized() has been called on it. If on is FALSE the
264 context has not been initialized.
265 See also initialized().
267
269 If on is TRUE the context has had a window created for it. If on is
270 FALSE no window has been created for the context.
271 See also windowCreated().
273
275 Swaps the screen contents with an off-screen buffer. Only works if the
276 context is in double buffer mode.
277 See also QGLFormat::setDoubleBuffer().
279
281 Returns TRUE if a window has been created for this context; otherwise
282 returns FALSE.
283 See also setWindowCreated().
285
288 http://doc.trolltech.com/qglcontext.html
289 http://www.trolltech.com/faq/tech.html
290
292 Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
293 license file included in the distribution for a complete license
294 statement.
295
297 Generated automatically from the source code.
298
300 If you find a bug in Qt, please report it as described in
301 http://doc.trolltech.com/bughowto.html. Good bug reports help us to
302 help you. Thank you.
303 The definitive Qt documentation is provided in HTML format; it is
305 located at $QTDIR/doc/html and can be read using Qt Assistant or with a
306 web browser. This man page is provided as a convenience for those users
307 who prefer man pages, although this format is not officially supported
308 by Trolltech.
309 If you find errors in this manual page, please report them to qt-
311 bugs@trolltech.com. Please include the name of the manual page
312 (qglcontext.3qt) and the Qt version (3.3.8).
313Trolltech AS 2 February 2007 QGLContext(3qt)