[Gary Bidwell]

Hi all,

I'm looking for a mip_matteshadow (from mentalray) equivalent in maxwell.

What this shader does, is to catch shadows, reflections, indirect lighting etc. from the 3d elements and render these on top of the backplate or hdr in camera.

(For those that use V-Ray I think it's the equivalent to the V-Ray wrapper - allowing the background colour to come through the shader.)

Cheers,

Steve

[Gary Bidwell]

ok, so you can make the ground plane a matte material in the Global parameters.

I've switched on shadows and material ID.

When the image goes off to render in maxwell (the host package is maya), the floor plane gets knocked out to black but I'm not sure how to access the shadow pass?

Cheers

[brodie_geers]

Well first of all when you are doing a shadow pass by default no material will catch shadows so it will be a white image. For each material you want to catch shadows you must go into the material properties and check the "Shadow" box to turn it on. Then when you render multiple passes in Maxwell Render you should see a little circle for each pass (I think it shows up in the lower right corner of the render window). Mouse over each of those circles to see the various passes.

-Brodie

[Gary Bidwell]

Hi Brodie, cheers for the info.

So you can output a shadow pass that hits the floor plane but not the reflection, refraction, indirect light etc.?

How would one render out these passes?

Or if this isn't possible is there a way to have the spherical hdr contributing to lighting, reflection etc. but to have the backplate actually in the camera view and somehow have this pick up shadows, reflections, etc.?

Cheers,

Steve

[brodie_geers]

I'm not sure I fully understand your dilemma. Are you trying to render an object with spherical .hdr lighting and have shadows under the object as if it were actually sitting on the spherical environment?

I haven't done this but I gather that in Maxwell it's a bit more involved than some other programs. You'd do one rendering of the object and it's environment. Just the 1 "beauty" pass for this render.

Then do a separate rendering exactly the same but this time add a plane below your object to act as a shadow catcher. Apply a material to it in which you've checked the Shadow box (this should be the only material in the scene which will receive shadows). This time again run only one pass but only the Shadow pass. This render should go relatively quickly compared to the beauty pass.

Then composite the 2 renderings together in Photoshop with the shadow layer set to multiply.

-Brodie

[Gary Bidwell]

Yep, that's exactly what I'm after - the shadows under the object as if it were sat on the hdr.

But I also want the reflection, refraction, indirect lighting etc.

The reason this is the way I want to go is because I will be using the spherical hdr for lighting and reflection but will be comping the shot in to a high res backplate image of the same environment.

That's where shaders like mip_matteshadow and the V-Ray wrapper come in. You still have to do some comping but you get all the info/passes you'd expect from the object being sat in the shot.

Cheers,

Steve

[brodie_geers]

I'm still a little fuzzy on what you're going for and don't quite have the time to research what exactly those other shaders do but I'll mention a couple things that might help.

1. You can check Matte in the material properties. As I recall this will cause the material to be excluded from the render but will still affect the scene in terms of reflections and shadows

2. If you've got an hdr to light your scene and a backplate for your background you can do that within maxwell. In the IBL channels place your backplate in the Background slot and check Screen Mapped (so it knows it's a flat image, not spherical). Then place your spherical environment into the other 3 channels (reflection, refraction, illumination). Note that you'll have to make your backplate an .hdr format image beforehand and you may loose some compositing flexibility but this can be handy sometimes.

-Brodie

[Gary Bidwell]

no worries.

Basically, I want to render my cg object using the hdr and I want a render where the cg object casts reflection etc. on to the floor, as if it's sat in the environment.

I turned on the Matte and Shadows option but I only get shadows showing in passes, nothing in reflections.

cheers.

[brodie_geers]

Sorry, i didn't describe that very well. Yes, the shadow pass will only show shadows. If you run the regular Render pass I think you might get closer to what you're looking for in terms of reflections although it'll need something to reflect off of. If you're just wanting the reflections of the object you'll also find an option under the Render pass which should allow you to choose Diffuse+Reflections, just diffuse, or just reflections. That last option might be useful to you if you're just wanting to comp in the reflections separate.

You'll find that for this sort of work Maxwell tends to require a number of separate renders rather than being able to do one render with a bunch of different passes that allow you to do all you want. It's a workflow issue I hope will be eventually resolved. v2 added a number of new pass options and I hope to continue to see more.

-Brodie

[Gary Bidwell]

cool. Cheers for the info. I'll do more testing.

It would be cool to have a render pass system that saves out all options in one go.

Thanks again,

Steve

[brodie_geers]

Well, if you check a number of render channels and set a save pass it will indeed save out each of those images. There's also a photoshop plugin which will allow you to just drag your .MXI file right into PS and it will sort all of the channels into layers for you which is nice.

However, there are still limitations when it comes to what you're doing. For example, you can't render diffuse and reflection channels separately as 2 channels in 1 pass (seems like an obvious thing to incorporate but still not there yet). Also as in the case of wanting a shadow catcher, there's not really a way to do all you want in 1 render with multiple passes.

-Brodie

[Gary Bidwell]

I was thinking for catching the reflections etc. on the floor I might try a camera projection of the backplate in the reflectance 0 and 90 on a floor plane. Then I could comp this on in post.

cheers

[brodie_geers]

Interesting idea. I'd like to see the results if you're able to post them later.

-Brodie

[Gary Bidwell]

Hi Brodie,

here's a really quick test:

http://imageshack.us/photo/my-images/83 ... 0000c.jpg/

Not sure it's gonna be the best solution. I can see there would be issues with where the edge of the floor reflects in the objects.

Cheers,

Steve

[Mihai]

With 2.5 you can do this in one go, no need to do two separate renders:

- Make your ground plane as you did in the image, with a texture similar to the ground in the hdr so the reflections and lighting cast from the 'ground' to the objects match more or less. What you could do to avoid those sharp reflection cutoffs from the small plane is make the plane a little bit bigger but also add an opacity map to it so it slowly disappears at the edges into the hdr background. Use this black and white opacity map as a Layer weight for the plane material. The disappearing edges being far from the actual objects, they won't affect the lighting on the objects.

- Turn on the shadow option from material properties in the material applied to the plane. This will turn it into a "shadow catcher"

- Hide the plane from camera

- Turn on render channel, shadow channel, alpha channel

- Your render will only have the alpha of the objects, not also the plane, but the shadow channel will still show you the shadows cast on this hidden plane.

- Cut out the object using the alpha as usual, paste it in the back plate, put the shadow channel on the top most layer and set it to multiply blending mode

Tweak until content