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Andrew West

Glass in form.z

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I have always needed my glass to look absolutely perfect in Form.z as all of my work is architectural.    The down side is that I have to use a double transparency to achieve this.  To achieve this I use Accurate glass with a transparency of zero and then I use Simple Transparency to add the transparency back in.  This is a known no no when it comes to render times.  However, it is the only way that I can get a glass that looks accurate at all.   The down side to this aside from increased render times is a diagonal shadow/ anomaly across the window that most clients don't notice.  Now I have found an additional problem. Do to the fact that I am under the gun to get a project out immediately I went back to a non double transparency material for my final render.  The final render looked great until I opened it up in photoshop and tried to eliminate the alpha background so that I could put in my own.  The alpha was a complete white image with no data of the transparent glass at all. This is an interior shot so essentially the view out the window which should have been and alpha grey scale was gone.  Lesson learned.  Never going to do that again.  Back to double transparency.

AW

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It's a long time since I used renderzone (mostly using Maxwell nowadays), but regarding the glass, yes the double transparency is a no no. Play with the glass setting a bit more until you get acceptable results and I find modelling the glass with a thickness or use a double glass pane gives a better double image reflection that looks better than a clean mirror reflection.

The diagonal shadow thing you mentioned can be gotten rid of by reducing the minimum ray contribution in Raytrace options (I think it's default is set at 10%).

The alpha channel being white could be that your light is not set to be transparent?

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Hi Andrew,

 

Yes, as Des notes, the Minimum Ray Contribution controls the "minimum reflection effect" that will be seen (so reflections of less than that value are ignored to speed up the rendering).

 

Glass Reflection has a Refraction component, which causes the light to bend as it goes through the glass.  This can not be achieved with an Alpha Channel image that does not yet exist, so that is why you lose the alpha transparency in that case. Instead of using a Glass Reflection, if you use a Mirror Reflection with a smaller amount of Reflectivity in conjunction with a Simple (or Center Edge) Transparency, you should be able to get what you want without the added render times.

 

Does this help?

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...I use Accurate glass with a transparency of zero and then I use Simple Transparency to add the transparency back in.  This is a known no no when it comes to render times.

Do you mean Accurate glass with a Transmission of zero? (there is no Transparency as such under the glass shader.) I thought that as long as Transmission is zero, it is OK to use Transparency - it is only when both Transmission and Transparency are something other than zero that you are "doubling up." What about using the metal shader - is that essentially just glass with no Transmission parameter?

 

On another note, for glass I always turn the refraction to 1 (as refraction through a glass plane in an architectural model is largely irrelevant.) I haven't tested this in quite some time but I seem to recall refraction causing a hit in render times. Though the refraction parameter likely doesn't come into play if the Transmission is zero.

Edited by rich f

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Rich

It is my understanding that if you use accurate glass as a material even if you set the transmission to zero and then add a simple transparency you are creating a double transparency. I think that their is an underlying transparency factor that still meeds to be calculated even if zero.   That said I have tried to use the accurate glass material as is and I do not like the results.  As a result I do double transparency and live with the extended render times. 

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