glass

# 1 05-12-2010 , 12:55 PM

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I want to assign a super-quick glass like material to face; to approximate a window. I selected the face assigned a blinn and turned the transparency up. I thought it seemed too easy and i as right as when i rendered the view it hadn't changed.
I turned raytracing on in the material too...

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# 2 05-12-2010 , 01:04 PM

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scrub that - it's working now... :-\

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# 3 06-12-2010 , 03:38 PM

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Sorry Se7enhedd to hijack your thread, but a thread named Glass is where I thought this Q. belongs.
Nilla I have started your HDR glass tute because I have a glass topped table in one of my WIPs. Learning lots user added image

thx.

But two questions.

(1)The refraction limit, I put several things on top of my table just to have something to reflect (all odd OBJs I have here and there) Several plain colored lambert materials and Vegeta who I assigned my Glass_S. At a limit of 1-2 I ony had the table top and one glass (left one) looking OK I (other glass things renderefd black and shiny. I upped it to 6 and the ball the table top and the two glasses rendered OK but Vegeta was Black, and there were/are no reflections of him on the table. So I upped the Limit to 20 and ALL my glass went black. Fiddled with settings and couldnt get him to render properly so I took him out. What is the limit 'Limiting' exactly? how many objects in the render can have refractions or how many times a ray of light can be refracted. Like if light gets refracted by a pane of glass and then hits a wine glass (going through two surfaces) is that needing 3 refractions limit. Why did going up to 20 screw up everything?

(2) Any idea why I get this weirdness in the right hand glass?

Want to add this is the best looking image I have ever created in 3D. Thx to both of you (David too).I didnt really get lighting until a few days ago. I still dont really get creating displacement/bump maps. Coloring in my model is the best I can do. And they always look crap when rendered. This table is GOING to have a procedural wood texture (under the glass top) but havent worked that out either. NEway thx again.

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Last edited by 3dStudent; 06-12-2010 at 03:52 PM.

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# 4 06-12-2010 , 05:48 PM

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You're welcome 3dStudent, I made that tutorial because I had a lot of problems with glass when i started rendering in Maya. I think you've succeeded in getting glass, there's enough light in that scene and it's refracting quite well. Getting glass to look good in essence comes down to one thing which is having enough light and creating some sort of realistic reflections. It's the same for metals and any highly reflective material, you need the reflections to work and the rest after that just comes down to minor tweaks. This is why things like cars, metallic and glass objects in isolation are commonly lit with Image Based Lighting, you just need to find a good HDR probe that works. I have not been able to get glass that can compete with something that uses mia_material_x and IBL.

For refraction & reflection limits they need to be counted and they are controlled in the render settings and on the shader itself if you use something like blinn because rendering refractions & reflections takes such an incredible amount of time. I was rendering an interior scene a while back and after I added glass on the table the rendering time went from 1 to 8 minutes(!). Because your raytracing the camera shoots out rays that calculate the surface and if you have one glass in front of the other you'd need a minimum of eight and so on, I usually count surfaces while Dave likes to crank it up from the start doesn't really make a difference in most cases(we're always having childish competitons about who gets the best render in the end whatever we're lighting user added image

). When you adjust these limits there's also the trace depth which determines how far into a surface you go, if this attribute is not adjusted up as well you'll get problems of this kind where the surface is not transparent enough and you get black areas occuring in your glass. I've forgotten this myself numerous times and been sitting there trying to figure out what went wrong, so this would be my guess for why you're having problems, different types of geometry would respond differently to trace depth being set too low try adjusting it and see what happens.

For the right hand glass it looks like some sort of very strange refraction or reflection. I find that sometimes I sit around and wonder what on earth is causing a weird patch until I reallise it's a reflection. You train your eye gradually to recognize reflections, and I can't figure out where that red patch is coming from. You're using the environment chrome texture which does play tricks sometimes, disconnect it from the shader and go search for an image on google instead can be anything and connect that into the reflected color instead and see what happens.

One thing to keep in mind as well when you set a refractive index is that there isn't a fixed value, for glass it would range between 1.4 - 1.8 normally, but the best glass render I ever got in Maya software with a blinn used a IOR of 1.2 so if it doesn't look right don't be afraid to change it.

For procedural wood we have several you can download and see how they're built they'll be on the site again in two days when we get the resources section up. What you use is a ramp and blend color node on a reflective material. Because you have a poly plane there you don't need to worry about UV's so you can go to cgtextures.com and try a bitmap instead, they've got great wood textures.

Hope that helps,
Nilla

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# 5 06-12-2010 , 11:20 PM

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By Trace Depth do you mean Raytrace Shadow depth? if not I can't find what your referring to.

I'm also slowly doing your lighting tutorial (this scene doesnt show that as I've merely thrown in two spots) In my previous renders I didnt have any visible shadows, I mistakenly thought they were there but were washed out by my lazy lighting. Turns out I didn't - when I played with Raytrace Shadow Depth I got some... You've taught me something else user added image

not what to do with that odd patch, but still good.

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# 6 06-12-2010 , 11:40 PM

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@3dStudent Just wanted say sometimes glass in Maya can be a pain the ass. Your not alone. Best of luck with it.

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# 7 07-12-2010 , 10:30 AM

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Yes I mean the ray depth limit for raytrace shadows, and also the max trace depth under raytracing in the render settings for mental ray. The last one should come to the sum of your reflections and refractions that you have set above. These are the two common things that will give you black glass as the rays shot out during raytracing are not getting through the surface properly.

When you get odd things like that patch it is usually some sort of strange reflection, a while back I was rendering a plastic ashtray and I got a similar thing to what you have there and I couldn't figure out why as I was rendering in isolation. As I moved the camera I understood that it was actually a reflection of the side of the ashtray that became detached at a certain angle and ended up giving this strange round patch at the center. So if this happens, the best thing to do is to move your lights or camera around a bit it usually fixes the problem and also tells you what caused it in the first place.

Glad to hear you're watching my lighting tutorial, geometry based light sources are very interesting to work with. One thing in your render at the moment, you have several lights with shadows turned on so the shadows are appearing in all directions. In most cases you only want one light to cast shadows as this is what will set a clear lighting direction in your scene so if you turn off the shadows for the other lights you'll see it will look a lot more realistic. Keep going, nice work so far user added image

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# 8 07-12-2010 , 12:06 PM

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Hey 3D looks good...better than mine by a mile LOL...and Im with david 110%...glass is a pain in the coight...just like a fresh Queensland pineapple has been insterted sideways...good luck mate.

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# 9 07-12-2010 , 01:49 PM

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I had a few of these whilst TRYING to get this damn HDR Glass out....damn thing!!

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# 10 08-12-2010 , 01:06 AM

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Nilla I'm only up to watching Shadow Linking tute, so if you covered it somehwere in Lighting Tute or HDR Glass tute ignore this. But curious if there is anyway to do reflection linking for the spotlights. I get ugly hotspots on my glass table and the shiny Parquet flooring in my House WIP from most angles, can I make the spots light a scene give shiny highlights on some surfaces like the wine glasses but not on others?

I've spent the last day or so playing with Wood textures for my table and Parquet floor as that odd spot in one of my glasses still eludes me- and gave me the #$!%'s So I took a break from Glass and lights. I dont need that mesh anywhere, just thought it presented a problem I'd better learn how to deal with.... The artifact goes if I move the camera further away and it seems to be a refraction of 35 degrees or so (played with moving a bright yellow plane around my scene), what I dont get is if it's a mere refraction why it has such jagged edges?

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# 11 08-12-2010 , 11:43 AM

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Reflectivity is a property of materials not lights so you can't reflection link spotlights as reflections will be determined by your material attributes. The ugly hotspots you're getting are specular highlights, and these you have a very high level of control over. A specular highlight is in fact a reflection of the lightsource itself, so if you have visible light sources in a scene you need to think about the size of these specular highlights. The second thing that determines specular highlights are the type of material you're trying to mimic, if you don't get the size and brightness of a specular highlight right you won't be able to sell a material. Glossy materials like glass and plastic will have very tight specular highlights with a whitish color, whereas rougher materials like rubber or wood would have broader less bright specular highlights. You use the specular color slider to tone down specular highlights on a material, and there's very few scenarios where you work with colored specularity - metals would be one of these exceptions. The natural way to color your specular highlights would be by using colored light sources, as this is how it would occur in the real world.

The best way to wrap your head around this is to place some different objects like a porcelain mug, a glass and some plastic objects on a wood table and look at how they interact with the light. Then try to mimic what you see in Maya, keep in mind that almost all materials have some sort of specular highlights once you're looking for it. You can also control if specular highlights will occur at all on the spotlight itself by turning on/off emit specular. Just like with shadows it's usually the most natural way that one light will trigger specular highlights on a material and the other lights will be set to emit diffuse only. I can see in your render on the glass ball that you have three specular highlights, so if you leave emit specular on for just one light you'll get a better result.

You can also use specific spec lights when you want to boost specular highlights in a material by setting a light to emit specular only. If these lights hit other materials in your scene they need to be light linked.

The reason for the jagged edges would be that light bends when it goes through a refractive material, you'll see this in the real world as well if you look through thick glass. It would just be more pronounced in cg render and cause this sort of pixelation I think.

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# 12 09-12-2010 , 04:45 PM

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Have a lot to digest thx to your help here and your tutes.. Think the time for QnA is sadly over. No amount of theory will replace the need to practice what I think has finally seeped in.

I still need to learn my way around the interface it seems (thought I had that down) Alot of my inability to follow your advice stemmed from this.

First off I spent hours looking in my Material and Render settings for Trace Depth...
Then I think Reflective Limits and Refractive Limits werent doing what I expected/what I thought you were saying they would- because I still hadnt found the correct tab (quality) in the correct tab (mental ray) of my render settings. I fiddled with Mental ray options everywhere but there. Got all that worked out and then last night was well on the way to a great image and incredibly pleased with myself, I had a cookie on a spot casting a shadow of a woman with wine glass in hand on a wall I put behind this table... I had a nice purplish directional light. And I needed a bit mor light to really bring out the Glasses on the table (beither with a weird patch in the middle) And then a truck hit a power pole at the end of my street and everything went black.... hadnt saved in hours and I lost it. )in more ways than one)

Just opened Maya and about to try and redo what I did last night, texture files and that cookie are still good, just need to recreate the lighting and refiddle with all those limits and depths and... that should be my last post on this thread for awhile. Not quitting just going to immerse myself in the doing rather than just talking about it.

Thx again.

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# 13 09-12-2010 , 07:18 PM

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Practice makes perfect 3dStudent user added image

That's why we believe in project based training. Remember to press F1 for the Maya help files when you get stuck looking for specifics like trace depth, getting into the habit of searching these when you're stuck for small things will save you so much time when you're learning Maya. I spent hours searching for things in the interface before Dave told me to learn how to use the help files instead, I just didn't think about it.

I also think you're doing really well, I was cleaning up my scene files yesterday and I found something called "My First Glass" I tell you it was very scary user added image

Dave tricked me into learning Maya only because I like to draw and I broke a lot of stuff along the way because it was so frustrating. Also I used to show him my renders and he'd just say "hmmm well, well" and I'd get so angry so it's not always easy. It took me a year to get something I was truly happy with, and remember it goes in bursts suddenly things just come together for you.

For loosing your scenes it's terrible when that happens, I'm bad at saving and I've lost some of my best work this way that I've not been able to recreate. One thing you can do, at least in Maya 2011, is to turn on autosave where Maya will automatically save your scene every so often. You get a lot of unneccessary scenes building up on your harddrive when you use it so you need to go in and delete stuff from time to time but it does prevent you from loosing your work and having to start from scratch.

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# 14 09-12-2010 , 09:28 PM

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Yeh autosave is good...but as Nilla said it does save a fair bit and can get cluttered. I prefer doing it manually....it takes practice but eventually the 'CTRL s" becomes a habit. It doesnt take much to get used to it....depends on your preference though.

Good luck mate

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# 15 10-12-2010 , 12:45 AM

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So needs tweaking but basically this is what I had the other night. (tried to exagerate the nighttime feel I had a hint of last time, I shouldn't have -shrug- Its too dark) Both times I went awry lighting the back wall, its either too dark like this considering the amount of light in the rest of the room, or I wash out the cookie and dont get the whole lit from that window feel. Plus I know the shadows on the table are going the wrong way....

But still a yippee for me user added image

Figure I'm halfway to being able to produce something that looks half decent (thats 1/4 of the way there right?)

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