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imported>Eliddell: Created page with "== 3D graphics with OpenGL == The de facto standard for rendering 3D graphics today is [http://www.opengl.org OpenGL]. Implementations of this specification come with Micro..."

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Created page with "== 3D graphics with OpenGL == The de facto standard for rendering 3D graphics today is [http://www.opengl.org OpenGL]. Implementations of this specification come with Micro..."

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== 3D graphics with OpenGL ==

The de facto standard for rendering 3D graphics today is
[http://www.opengl.org OpenGL]. Implementations of this specification come
with Microsoft Windows, Mac OS X and XFree86 and often support the hardware acceleration
features offered by modern graphics cards. OpenGL itself only deals with rendering on
a specified area of the framebuffer through a ''GL context'' and does not have any
interactions with the toolkit of the environment

Qt offers the widget QGLWidget
which encapsulates a window with an associated GL context. Basically, you use it
by subclassing it and reimplementing some methods.

*Instead of reimplementing paintEvent() and using QPainter to draw the widget's contents, you override paintGL() and use GL commands to render a scene. QLWidget will take care of making its GL context the current one before paintGL() is called, and it will flush afterwards.
*The virtual method initializeGL() is called once before the first time resizeGL() or paintGL() are called. This can be used to construct display lists for objects, and make any initializations.
*Instead of reimplementing resizeEvent(), you override resizeGL(). This can be used to set the viewport appropriately.
*Instead of calling update() when the state of the scene has changed - for example when you animate it with a timer -, you should call updateGL(). This will trigger a repaint.

In general, QGLWidget behaves just like any other widget, i.e. for example
you can process mouse events as usual, resize the widget and combine it with
others in a layout.

[[Image:opengl-gears.png|frame|center|OpenGL screenshot]]

Qt contains some examples of QGLWidget usage in its <tt>demo</tt> example.
A collection of tutorials can be found
[https://web.archive.org/web/20020206053805/http://www.libsdl.org/opengl/intro.html here],
and more information and a reference of OpenGL is available on the
[http://www.opengl.org OpenGL homepage].

== High-level interfaces ==

OpenGL is a relatively low-level interface for drawing 3D graphics. In the same
way QCanvas gives the programmer a higher-level interface which details with
objects and their properties, there are also high-level interfaces for 3D graphics.
One of the most popular is Open Inventor. Originally a technology developed by SGI,
there is today also the open source implementation
[http://www.coin3d.org Coin], complemented by a toolkit binding to Qt
called SoQt.

The basic concept of Open Inventor is that of a ''scene''. A scene can be loaded
from disk and saved in a special format closely related to
[http://en.wikipedia.org/wiki/VRML VRML]. A scene consists of a collection of objects
called ''nodes''. Inventor already provides a rich collection of reusable nodes,
such as cubes, cylinders and meshes, furthermore light sources, materials, cameras
etc. Nodes are represented by C++ classes and can be combined and subclassed.

An introduction to Inventor can be found
[https://web.archive.org/web/20031115053554/http://www.motifzone.com/tmd/articles/OpenInventor/OpenInventor.html here]
(in general, you can substitute all mentions of SoXt by SoQt in this article).

''Initial Author:'' [mailto:bernd@kdevelop.org Bernd Gehrmann]

[[Category:KDE3]]
[[Category:Architecture]]
[[Category:Developers]]

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