AutoCAD

What To Do About 3D Graphics Problems (Bug Watch AutoCAD Tutorial)

10 Apr, 2007 By: Steve Johnson

Interesting times lie ahead for 3D graphics users.


Make the Most of Your 3D Graphics
Last year, AutoCAD 2007's new 3D graphics engine introduced a range of new issues to be considered by users, managers and IT departments. Lots of people bought new hardware for AutoCAD 2007, especially graphics cards. Autodesk shifted the burden of 3D graphics calculations from AutoCAD to the graphics card and driver, so picking the right card became very important.

People thinking of buying cards for 3D use should first consult AutoCAD's Graphics Hardware List. This list is the result of Autodesk doing a great deal of tedious testing of various card and driver combinations. There's no way you or I could hope to reproduce Autodesk's testing efforts, so take advantage of Autodesk's work and read carefully before taking the plunge into what is a very significant portion of a system's expense.

Of course, buying a card approved by Autodesk doesn't guarantee a bug-free 3D experience -- far from it. The hardware and software combination that puts those pretty pictures on the screen is a complex beast doing a complex job. Sometimes it doesn't do the job properly. When something doesn't render properly in a game, it's not that important (unless you're very obsessive about games, in which case you probably don't have time to read this). When something doesn't render properly in a CAD application, it can negate the whole point of your expensively constructed model.

What to do? Drivers, drivers, drivers. The graphics card manufacturers are constantly updating their drivers, fixing lots of bugs you didn't know existed and improving performance too in many cases. Although I'm no fan of an automatic update-to-the-latest mindset, it appears to be the best thing to do in most cases as far as graphics drivers go. I reiterate: most cases, but not all. I've killed a system stone dead more than once by installing updated drivers that the manufacturer's Web site claimed were appropriate for the system. If in doubt, do some research first.

Also, make sure you keep your Autodesk Certified Hardware XML Database up to date. This list will tend to lag behind the latest drivers, so you may need to adjust the settings in the 3dconfig command to get the best use out of your system. If you have hundreds of users to support, you probably don't feel like doing this on each PC. If you're feeling really adventurous, you could distribute your own modified version of the XML file so AutoCAD doesn't automatically disable hardware acceleration. Obviously, you must take great care before doing so. Test carefully first and be prepared to restore a safe copy of the original as a fallback.

Vista Brings a 3D Graphics Bonus for XP
If you thought the year 2006 was an "interesting" time for 3D graphics, then 2007 promises to give you more of the same and then some. Windows Vista has arrived, bringing with it a whole new world of 3D graphics issues. The Vista graphics system is completely different. In particular, Microsoft has dropped direct support for the OpenGL standard in favor of its own proprietary system, Direct3D.

What does this mean for those of you who shelled out large amounts for graphics cards with good OpenGL support during the AutoCAD 2007 cycle? It all depends on how well the manufacturer writes Vista drivers for your particular card. Despite the extensive prerelease testing period, graphics card manufacturers and application writers generally aren't well prepared to cope with this change. In the short term, at least, you can expect many 3D applications to perform badly on Vista. You may have already read horror stories about Vista performance, but these are largely based on testing using early or prerelease drivers, and your mileage may vary.

Expect things to improve as time goes on. In a few months, the Vista graphics issues should settle down and just about everyone should be on top of things. In a year, high-performing cards and drivers will become more plentiful, more powerful and cheaper. Then would be a good time to move to Vista, if that's what you intend to do. Right now would be a bad time to move, unless you have particularly pressing reasons for doing so.

For those who intend to stick with Windows XP for a while, there is an accidental bonus. AutoCAD 2007's graphics system uses OpenGL. Because AutoCAD 2008 is supported under Vista, the AutoCAD graphics system needs to provide Direct3D support. That's the only option you get in Vista, but in XP AutoCAD 2008 lets you choose between OpenGL and Direct3D.

Why is this relevant to "Bug Watch"? Because you can use it to work around 3D display bugs. To some extent, the workaround is done for you. Autodesk writes its Hardware XML database based on its test results. If a given card-and-driver combination works best with OpenGL, then the database instructs AutoCAD to use it by default, so you'll automatically avoid some bugs. If you find 3D graphics bugs getting in your way, you can try using the 3dconfig command to tell AutoCAD to use Direct3D instead. This change may alter performance and stability for better or worse, but it also may fix what looks like a glitch in your model.

Clayton's Cylinder (All Releases)
A problem that has been around for a while is that some objects don't display as accurately as they used to. I covered some of these issues earlier, but here's another one. Cylinders aren't cylindrical. Instead, they are displayed as a series of facets. That wouldn't matter too much if there were enough facets, but for some real-world drawings, AutoCAD's cylinders are far too chunky. AutoCAD has always done this, but the problem is much more noticeable on some systems using AutoCAD 2007 and later.

figure
Steel tank drawing in AutoCAD 2007.

The image above shows a drawing of a steel tank with some joists that butt up to the inside wall of the tank. However, AutoCAD is displaying them as if they poke right through the tank to the other side, as zooming in shows more clearly.

figure
Close-up of problem objects in AutoCAD 2007.

Along the top edge, you can also clearly see the extra lines caused by the faceted nature of what should be a smooth cylindrical surface. Depending on your release, you may find the problem also appears in Plot Preview, even though an actual plot comes out correctly. This problem somewhat negates the point of the plot preview. In some releases, the plot is wrong too.

figure
Plot Preview in AutoCAD 2007.

Workaround: The various settings you find in Tools / Options / Display won't help you, unfortunately. You may find turning off or adjusting the settings for dynamic tessellation in 3dconfig's Manual Tune section helps in some cases, as shown below.

figure
Nearly fixed -- the result of turning off dynamic tessellation in AutoCAD 2007.

If that doesn't help, the only thing you can do is to fudge the issue by editing the objects. In this case, you can either chop off some material from the joist ends or you can split the cylinder up into smaller sections, resulting in finer tessellations.

Email Problems
Due to technical issues that are entirely my fault, my Cadalyst e-mail has been vanishing into a black hole for more than a month. If you sent me some useful information about AutoCAD bugs between mid-February and the end of March, please resend it


AutoCAD Tips!

Lynn Allen

Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!
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