Home · Overviews · Examples 

QGLFramebufferObject Class Reference
[com.trolltech.qt.opengl module]

The QGLFramebufferObject class encapsulates an OpenGL framebuffer object. More...

Inherits .


Detailed Description

The QGLFramebufferObject class encapsulates an OpenGL framebuffer object.

The QGLFramebufferObject class encapsulates an OpenGL framebuffer object, defined by the GL_EXT_framebuffer_object extension. In addition it provides a rendering surface that can be painted on with a QPainter, rendered to using native GL calls, or both. This surface can be bound and used as a regular texture in your own GL drawing code. By default, the QGLFramebufferObject class generates a 2D GL texture (using the GL_TEXTURE_2D target), which is used as the internal rendering target.

It is important to have a current GL context when creating a QGLFramebufferObject, otherwise initialization will fail.

OpenGL framebuffer objects and pbuffers (see QGLPixelBuffer) can both be used to render to offscreen surfaces, but there are a number of advantages with using framebuffer objects instead of pbuffers:

  1. A framebuffer object does not require a separate rendering context, so no context switching will occur when switching rendering targets. There is an overhead involved in switching targets, but in general it is cheaper than a context switch to a pbuffer.
  2. Rendering to dynamic textures (i.e. render-to-texture functionality) works on all platforms. No need to do explicit copy calls from a render buffer into a texture, as was necessary on systems that did not support the render_texture extension.
  3. It is possible to attach several rendering buffers (or texture objects) to the same framebuffer object, and render to all of them without doing a context switch.
  4. The OpenGL framebuffer extension is a pure GL extension with no system dependant WGL, AGL or GLX parts. This makes using framebuffer objects more portable.

Note that QPainter antialiasing of drawing primitives will not work when using a QGLFramebufferObject as a paintdevice. This is because sample buffers, which are needed for antialiasing, are not yet supported in application-defined framebuffer objects. However, an extension to solve this has already been approved by the OpenGL ARB (GL_EXT_framebuffer_multisample), and will most likely be available in the near future.

See also Framebuffer Object Example.


Copyright © 2008 Trolltech Trademarks
Qt Jambi 4.3.4_01