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I would like to make an important feature request. Please see the attached image.

The scaling in the image is all wrong, but I made everything the way I did to make my point clear. What is important in this example is that I have taken the HDR background image and made a grayscale mask from it. I then spherically mapped this mask image onto a sphere that surrounds the orange box inside it. This mask is applied to a mix material so that the sphere is part transparent, part opaque. Inside the sphere, the orange box is kind of hard to see, but you get the point...Box inside a sphere with holes in the sphere created from a mask, with the mask coming from the original HDR image.

Now here is the frustrating part. Since the sphere is now acting as a shadow maker, partially blocking light from the HDR image, this sphere & mask can be used to cast shadows onto the box...IF ONLY THE SPHERE COULD HAVE AN "UNSEEN BY CAMERA" OPTION, AND AN "UNSEEN IN REFLECTIONS" OPTION. What is cool about this possibility, is that without creating extra geometry to cast shadows, we can let the HDR image provide that information for us. It is not necessarily accurate, unless the box is centered around the world origin, but that point is moot. What is important is that a faithful set of cast shadows can be realistically cast onto the box with minimal work.

This means that HDR images can now be made to cast shadows realistically, though not necessarily precise. But again, that point is moot. What is imnportant is the overall effect. If the box is NOT centered about the world origin, then parallax error between the HDRI and the mask may completely block the direct rays from the Sun. But that is not really an issue when we can rotate the sphere to get the best possible alignment with the Sun and the best looking cast shadows.

Now, if we can ALSO tell Octane to let the holes in the mask be considered as pathways for direct light, we can set the exposure of the light that passes through it. In addition, we can set the sphere opacity to less than "1" to control the darkness in the shadows.

THIS DOES NOT AFFECT THE GENERAL EXPOSURE COMING FROM THE HDRI. It only allows us to add EXTRA exposure control for light passing through the holes in the mask.

Also, the scale of the shadows and their sharpness are easily controlled by the radius of the sphere relative to the box's size.

This means that we can fairly easily, perhaps with some work in Photoshop, stop direct light in the HDRI, like from the Sun, from casting into those areas of the scene that the HDRI is telling us are in shadow. Unfortunately, this method cannot prevent the HDRI Sun from appearing in glossy surfaces. But that is another issue for thought.

Since the "Unseen by Camera/Unseen in Reflections" options are critical here, this whole process only affects the diffuse properties of the box material. So this is all really acting as, I guess you could say, an HDRI occlusion mask.

The ONLY thing preventing this from happening in Octane right now, is that it does not give us the option of making a mesh unseen to the camera, and unseen in reflections. That to me makes this a vital addition to Octane, because the benefits are great for such a simple feature addition.

I agree that having control over visibility in reflections and refractions would be a great addition to the visibility controls.

I'm not convinced your idea is very workable but I love being proved wrong by interesting ideas so I'd love to see some results if we ever get that control in Octane.

T.

I did not know about the Object Layer Node. That is so cool. Thank you for the info!!!

This is WAY cool. Here is my first shadow test:
This kind of thing may take a while to dial in, but it looks promising.

The only problem as you say, is that the Object Layer Node does not prevent the reflections of the object from appearing. Big bummer. So until and if that changes, this technique requires doing a separate render where the affected objects that have glossy or specular materials are replaced by diffuse only, so the shadows and light leaks can be captured. Then it would have to be composited in Photoshop over the original render to provide an exposure-like adjustment for the areas receiving direct light.

'm not convinced your idea is very workable but I love being proved wrong by interesting ideas so I'd love to see some results if we ever get that control in Octane.

This seems workable. For the reflections issue, the only solution for now is compositing multiple passes in PShop. Actually, this test involved a shadow catcher pass, my light & shade pass, and a lone HDRI background pass. I tried to combine the shadow catcher pass and the light & shade pass in one single pass, but if the shadow catcher plane intersects the invisible sphere, that intersection shows up as a rendered circle. So it's not so invisible anymore.

A slightly touched up version to match the blur of the box to the HDRI, make the cast shadow less contrasty and get some bumpy shadow at the very bottom:
I also think that because this is a very simple box, with no rounded edges or textures, that if it seems to work with that, then I think the effect will be even better with a really complicated, more realistic mesh, since the basic realism of the mesh will be so much better.

I think I might try this with my car mesh. I'll just put the ball around it and see what happens.

Heheh...This is SOOOO cool. I am working out the bugs in this idea and I finally solved the too diffuse shadows problem. Couldn't figure out why the cast shadows had no sharpness to them even when the masking ball was made really tight to the mesh. It is because when you do the render for the light & shade pass, you have to take the HDRI into PShop and blacken everything but the light source. Otherwise, all of the light across the whole HDRI was getting through the mask ball at all angles. Now that I did that, I have essentially a point source of light, the Sun, and I'm getting the most gorgeous cast shadows of the forest on the subject (a car).

I hope I don't get disappointed when I composite everything in PShop.

Basically you just figured out how to add "light gels" to OctaneRender.

Heheh. That's right!

A fog volume would really be neat. with God Rays.

Light & Shade mask almost complete. Just need to render a bit longer to get the noise down. Took all evening to figure out how to get it to render quickly. Then I need to render a Shadow Catcher pass.

Couldn't resist posting this before all the noise was cleared up:
One nice thing about this is that you can cut the ball in half and let that cast shadows onto a Shadow Catcher plane, so that the shadows on the ground are correct also. To cut the ball in half, you just make sure half the mask is white in the Mix Material. Only problem right now is that using the Visibility-Off option with the Shadow Catcher causes the two to intersect. Until that is fixed, it may require some retouching in PShop.

So three passes were required to get the above example:
1. A bare HDRI background pass (Renders almost instantly).
2. A Shadow Catcher pass for the ground shadows (Typical render time).
3. A Light & Shade pass for the light and shadows on the car.

For the Light & Shade pass, the meshes needed to be given a pure white diffuse material, so that the resulting image on black would be grayscale with an optimal contrast ratio. This also means making sure you have no chroma in the light source. The best way to do that is to take your environment HDRI into PShop and create pure white areas for your light sources and black everywhere else. This is perfectly fine since you are only using the mask to adjust the exposure of the shadows on the car.

I used the resultant L&S pass as a mask in PShop. I created a duplicate of the Shadow Catcher Layer and applied the mask so that the light areas were removed, leaving only those areas to be shadowed. Then, I used a Brightness and Contrast adjustment to darken those areas, using Multiply mode at 63% opacity for the final effect.

Now that I know how to do this. This is a very practical and fast technique. What would REALLY help in Octane would be to have visual, mouse-driven Move/Rotate/Scale handles for meshes and material UVs. That would tremendously speed up the trial & error of getting the ball and meshes properly placed and oriented.

This COULD all be pretty close to a one render pass deal, if the Shadow Catcher and the ball would not fail together, and the ball would not appear in reflections. That would speed things up a lot, too.

So the feature requests that would really help out are:

1. Invisible objects should not appear in reflections.

2. When the invisible ball and shadow catcher are used together, that Octane does not render the intersection of the ball and shadow catcher surfaces. In my tests, the shadow catcher was a simple plane. So where it intersected the sphere, it rendered a disk.

2. Mouse-activated Translate/Rotate/Scale handles for objects.