ACG Tutorials

These are three tutorials on the topics of

• Billboarding,
• Recursive Portal Culling, and
• LOD rendering

in 3d computer graphics; which have been written as a contribution to the advanced computer graphics class held by Steffi Beckhaus and Kristopher Blom at the University of Hamburg in winter '05.

The project homepage can be found at acg.bspot.de - please check there for updates and bugfixes.

If you should encounter any bugs please take the time to send a bug report to 9boltze@informatik.uni-hamburg.de.

The tutorials themselves are written in XHTML+MathML, but utilize a java applet to visualise the techniques covered. Hence, to enjoy the full educational experience, you will need:

• the JRE 1.5,
• Firefox with the Java plugin installed,
• the correct fonts to display MathML-content, and

you will further need to trust me as well as Sun by confirming the respective requests from your browser, because the applet needs to install the JOGL native libraries on your machine to access your OpenGL implementation.

Please note that the application does not work completely stable yet. Especially, it will sometimes lock up the browser for no apparant reason when loading the page including the applet. This is more likely to occur when the page is reloaded or an applet has been viewed before in the same browser instance. In these cases, it is advisable to close the browser and start a new instance, although there also have been cases where the tutorials could only be run after a complete reboot of the system.

These problems could not be tracked until now, but it seems that they are rooted in the JOGL library and/or the underlying OpenGL implementation of some GPU drivers.

Some general problems with JOGL based applets are the following:

• The applet may not run if JOGL is already installed on your machine. There is currently no fix for this except deinstalling JOGL before running the applet.
• Slow framerates may be experienced if the Firefox Talkback Extension is enabled.

• A new version of JOGL (1.1.0) is distributed with the tutorial. This should fix some problems, especially a bug preventing the applet from starting under JRE 1.5.0_10.

• The JSplitPane used for the layout of the applet has been replaced by a custom component doing the job better and with (hopefully) less overhead. The different views can now be resized horizontally and vertically.

• A log window capturing stderr has been added to the top of the applet. This will inform you a bit about what's happening and - more important - show any uncaught exception if something goes wrong.

• The tutorial texts have been refined in various ways.

In the case startup succeeds, you will be confronted with the tutorial text on the left of the screen and the applet on the right.

The applet's area is further divided into three views, which show the same scene from the perspectives of different cameras. You can control the cameras' positions using the mouse - just try moving it in conjuction with different mouse buttons and the control key; it should be rather easy.

Please Note: Even if everything runs fine, startup takes some time and may give you the impression that something went wrong. Normal startup proceeds like this:

• First, the browser shows a blank screen and locks up completely for some seconds - this is when the JVM is started.
• Then, the tutorial page appears on the left, while the applet shows a blank screen with a progress bar at the bottom. Now the JOGL native libraries are loaded. If you didn't do so before, you will be asked to confirmed that you trust the author of the applet.
• Then, a text window will appear at the top of the applet saying "initializing", while the rest of it stays blank. This is when the OpenGL windows for the three views are initialized.
• Finally, the applet should show the three views as described above.

At the beginning, the scene will be pretty empty - what is shown here depends on the part of the tutorial you're currently working on. To indicate that, the text is separated into steps (see the thin blue lines), which get activated when you click on them. Furthermore, there are links in the text which will trigger events in the scene; e.g. show/hide objects, change the mode of operation of some algorithm, etc.

Further, there is a presentation-mode version of each tutorial, with a short set of controls instead of the actual tutorial text.

Well, so much for that. Here you go:

• PortalCulling (presentation mode)
• LOD (presentation mode)
• Billboarding (presentation mode)