Shadow Catcher and correct reflections -> here you go

[dionysiusmarquis]

Hi saw several requests for an Shadow Catcher which provides right reflection information. You'll see the diffuse color of your matte material in the reflection and refraction of other objects. For correct reflection/refraction you need the projected hdri color data.
Here's a simple setup to get the right color information.

Diffuse Material/Diffuse Color (matte) -> Image Texture (with your hdri image/horizontally mirrored) -> Spherical Projection -> Translate Transform.
Now Link your camera translation to the Translate Transform.

With red color applied to the matte diffuse color:

With the projected color:

[dionysiusmarquis]

Edit:
Added more self-explaining Images.

Is it somehow possible to mirror file texture nodes directly with octane?

[roeland]

You can change the UVW transform like this: first disable the aspect ratio lock on the right, then set the S.y (vertical scale) to -1. You can do this by clicking in the text field on the left of the slider.

--
Roeland

[dionysiusmarquis]

You can change the UVW transform like this: first disable the aspect ratio lock on the right, then set the S.y (vertical scale) to -1. You can do this by clicking in the text field on the left of the slider.

--
Roeland

I see, thank you. I was in Maya and there the transform restricted the input to min 0.0001. But in Standalone it works flawlessly!

[gordonrobb]

That's all well and good, and thanks for the clarification. Can't work that way (the camera values plugged into the projection like it is in standalone), in the LW plugin. I've asked the question over there, but so far, no answer.

That's why I was thinking, that if this can be done the way you are suggesting, it seems to me it would be better coded into the matte process.

[ROUBAL]

I understood nothing on that thread : do you mean that it is not possible to get reflection of real objects onto the shadow catcher ? Only fake environment with an HDRi ? What if you use no HDRi, but daylight instead ? Isn't it possible to add a transparent plane with glossy/reflective material under the shadow catcher ?

According to what I see on the images above, it is rather about reflections of the environment into objects... I don't see the relation ship with the shadow catcher, in fact.

[dionysiusmarquis]

I must confess the title is misleading. But the text should make it clear. This approach is more common as a background Image/hdri combination. The goal is to render a glossy Object into an 2D image with plausible reflections and refractions. This is achieved by projecting the background image or like in this case the hdri onto 3D objects. Theoretically its possible to convert the 2D image to 3d with this method quite well. In this example only the floor of the hdri is projected to 3d onto the matte plane. You can also find more about it under the term camera mapping.

Example with Background Image/ hdri combination: http://www.dmmultimedia.com/3dtips_11c.htm
Movie done with camera mapping: http://www.youtube.com/watch?v=iALi-Ko9wPk (base material 2d photos!)

Here is the same without the matte plane object (notice as it doesn't fit anyhow into the environment even if you would put in shadows):

[gordonrobb]

I understood nothing on that thread : do you mean that it is not possible to get reflection of real objects onto the shadow catcher ? Only fake environment with an HDRi ? What if you use no HDRi, but daylight instead ? Isn't it possible to add a transparent plane with glossy/reflective material under the shadow catcher ?

According to what I see on the images above, it is rather about reflections of the environment into objects... I don't see the relation ship with the shadow catcher, in fact.

This is about seeing the background either in reflection or refraction, on the object. Not, about seeing a reflection of the object, on the Matte object.

[ROUBAL]

Thanks you, it makes more sense now.

[dionysiusmarquis]

Not yet tested but it's now (since v 1.51) a build in behavior of the matte material! http://render.otoy.com/forum/viewtopic. ... 62#p177710