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Old 17th March 2012, 09:10 PM   #1
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Question Graphic glitch on AMD Radeon HD6970M (iMac 27" Mid 2011 - OS X 10.6.8)

Hello to everyone.

This is my first thread here, although every now and then I come here to take a look at the AC3D Forums.

I am having the following problem, quite difficult to describe in words; it would be definitely be better to post a movie, but anyway, I'll give it a try:
I have recently bought an iMac 27" (mid 2011) with an AMD Radeon HD 6970M graphic card with 2 Gigs of VRAM. Before I used an iMac 24" (early 2008) with an Nvidia GeForce 8800GS graphic card on wich I did not have the same troubles.
I cloned via Time Machine my entire System and therefore ended up with the new iMac with ALL that was on the "old" iMac, so I found myself with a working copy of AC3D for Mac on the new Mac as well.
Now for the problem.
While on the old iMac everything was fine, on the new iMac, when constructing objects in AC3D, when I have a semi-transparent surface OVER an opaque sutface, the semi-transparent is not always completely transparent. If I zoom in, I get a perfect transparency, but when I zoom out a bit, the transparency begins to fill up with some artifacts, made of diagonal lines. These lines are not "frozen", but they tend to move in a kind of circular way when I move my view around with the mouse. The more I zoom out, the more the lines become so thin that at some point, they are quite (if not at all) invisible. The more I zoom in, the more depth these lines tend to acquire until at some point, I cannot see what is shown under this semi-transparent surface.
This particluar error seems to be affecting ONLY the 3D view, while the orthogonal views are perfect.

I clearly suspect some glitches on the graphic card driver, but since Apple had not released (as always I may add!) any updates for my OS, I do not know how I may try to solve the problem.

I tried also to create and login onto my system as a completely new user with admin privileges, but the problem remained.

Now, the only thing I may try to do would be to re-install a fresh copy of AC3D, but I guess this would not be of great help. And before doing that, I wanted to try the AC3D Forums...

Anyway, I am writing here to see if someone else has encountered my same problem.
I want to point out that this seems much more a graphic glitch rather than a really big problem, since I can manage to work even with this error, but still, as for this particular trouble, sometimes I regret not being working on my old iMac, on wich the view was perfect!

Hope to receive some help from your experiences.

Thank you very much and please, excuse my bad english.


Last edited by MacCekko; 17th March 2012 at 09:14 PM.
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Old 18th March 2012, 05:18 AM   #2
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Default Re: Graphic glitch on AMD Radeon HD6970M (iMac 27" Mid 2011 - OS X 10.6.8)

If I understand what you are saying correctly, it's not a bug or fault. For transparency to work correctly, transparent surfaces need to be drawn last. If tranparency is to be done totally correctly, the transparent parts must be drawn in depth order and pixel by pixel, like you'd get in a ray-tracer.

AC3D doesn't sort the surfaces for transparency and even this wouldn't be enough for it to transparency to properly.

the artifacts you are seeing are probably just different ways that the graphics libraries handle drawing transparency and are nothing to worry about.

If you need a fully rendered image with transparency, you'll need to render the image with Povray or similar.

The solution in AC3D for windscreens, windows etc is to put the transparent surfaces in an object and put it at the bottom of the hierarchy so it is drawn last. This way you'll get the best preview image.
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Old 18th March 2012, 11:27 AM   #3
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Default Re: Graphic glitch on AMD Radeon HD6970M (iMac 27" Mid 2011 - OS X 10.6.8)

Thank you for your answer. I am well aware of the need of a transparent surface to be drawn last in the hierarchy, when possible. I've been using AC3D for a while now. But this is only a matter of ugly artifact that presents itself since the new iMac. Too bad, since it IS ugly!
Anyway, again, thank you for your kind answer.
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