MATERIAL TRANPARENCY BUG !

[Steven]

Hi. While I was designing a clear glassy beer buck, with beer in it, I met a bug. I experiment a little with simple objects to find out why I can see some objects through say a transparent sphere and why I cannot see other objects through that same sphere!

The picture below use four objects.
- Two cylinder and one sphere using the same transparent glassy material.
- One sphere with a transparent glassy yellow material.
http://www3.sympatico.ca/j.s.rioux/ClearGlass_01.jpg


The following picture clearly illustrates the problem I am running through.
When looking through the cylinder in the middle, I cannot see any of the other three objects throught it. Example, the picture illustrate that I cannot see the yellow transparent sphere.
http://www3.sympatico.ca/j.s.rioux/ClearGlass_02.jpg

Now, if I look through the yellow sphere, I can see the middle cylinder...
http://www3.sympatico.ca/j.s.rioux/ClearGlass_03.jpg

...however, I cannot see the inclined cylinder...
http://www3.sympatico.ca/j.s.rioux/ClearGlass_04.jpg

...and the clear white sphere!
http://www3.sympatico.ca/j.s.rioux/ClearGlass_09.jpg


If I look through the inclined cylinder, I see the yellow ball, the middle cylinder and the clear ball. Everything is looking as it is suppose to look!
http://www3.sympatico.ca/j.s.rioux/ClearGlass_05.jpg

http://www3.sympatico.ca/j.s.rioux/ClearGlass_06.jpg


If I look through the clear sphere, I see the middle cylinder and the yellow sphere correctly too...
http://www3.sympatico.ca/j.s.rioux/ClearGlass_07.jpg

but not the inclined cylinder!!!!
http://www3.sympatico.ca/j.s.rioux/ClearGlass_08.jpg


I just want to insist on the fact that the clear white objects on this picture use the same material. Only the yellow sphere use a different material.
- Also I notice that when manipulating some objects, this transparency bug can appear while before the manipulation, the transparent effect was ok. The type of manipulation can be surface, vertex, streching etc..
Note that the objects on the examples did not have any manipulation with
vertex or surface. I just made a cylinder and I make it taller. I have done another cylinder and I rotate it. And I use sphere to create the two balls.

- I notice that when I use the function duplicate or copy a transparent object, then the clone object demonstrate the transparency bug!

MY QUESTIONS

WHY?
WHY?
WHY?
What am I doing wrong?
Does acetaminophene can help? http://www3.sympatico.ca/j.s.rioux/mous_anm.gif

Thanks very much in advance.

STEVEN

[Andy]

You are not doing anything wrong - you descibed the problem beautifully.

AC3D does not sort the surfaces before rendering them. Transparent surfaces should be drawn after other surfaces and even then, they should be drawn in the correct order. You can still get problems from this sorting if transparent surfaces overlap.

Where you are getting different results, you are seeing the AC3D objects drawn in the order they lie in the overall hierarchy - e.g. objects at the end get drawn last. You can fix this to a certain extent by reordering the objects using the Tools->hierachy and ensuring transparent objects are at the end.

Adding this sorting to AC3D would slow down the rendering speed.
If you render your images using Povray or similar you will get a properly rendered picture where the transparencies are correct (because the rendering is pixel based).

Andy

[Steven]

Thanks very much Andy. Effectively the hierachy tool give me more power to control the transparency visual effects that I want to obtain in my design!

This picture show a MOS structure, very popular in todays CMOS technologies.

Explanation of the structure (for those who are interested)

"The red tab is the polysilicon gate. The aqua translucent structure represent the gate oxide (under the red tab) and with the LOCOS isolation (at each end) this glassy material is called silicon dioxyde. The yellow structures represent the impurities implantation into the grey silicon substrate. When a voltage is apply to the gate (red tab), the channel under the gate become conductive and a current can flow between the source and drain (yellow structures). The purple glassy structure is called field oxyde and it can be made of phosphosilicate glass. It is use to protect the underlying structure and serve to isolate the metal layer from the polysilicon layer (red tab). You can see some aluminum contact and a square column called "via" that connect the aluminum layer with the drain, source or polysilicon."

http://www3.sympatico.ca/j.s.rioux/MOS_1.jpg

http://www3.sympatico.ca/j.s.rioux/MOS_2.jpg

http://www3.sympatico.ca/j.s.rioux/MOS_3.jpg

As you can see the transparent feature is important to me. I will probably finish my beer buck this weekend. Beer always on weekends! A toast to you and your software.
Cheers,
Steven