Hello,

I have a problem with the attached scene: I would like to render scene as seen in the viewport, with the mesh and its material, but it keeps rendering the partticles.

I should be wrong somewhere in the particles settings but I really don't see where.

Thanks a lot,

Werwack

Not sure I know what you're expecting to see, but if it helps, this is what I get…(removed)

edit: I understand, but I can't see the problem either…

Thank you for your answer. Hum, I don't see what you get, has it been removed?

This is what I would like to have (see attachment).

Your mesh is in there but is being obliterated by the two Particle primitives that are also present in your geometry.

By default, if there is no instance attribute on the points or render attribute, default spheres of radius 0.1 are placed on each particle point. That is what you are seeing.


Append a Delete SOP and set the Geometry Type to “Particles” and clear the Pattern field (so that it is blank). Now MMB (MiddleMouseButton) on the Delete SOP icon and you see that there are no more Particle primtives present and you now get to see your mesh render not obliterated by your particles.

Great, thanks!!

Indeed I didn't know the particles were also visible in my Roots object. The MMB is of a great help for that!


The alpha transparency of the texture, which is clearly visible in the viewport, doesn't seem taken in account in the rendering. Is there something to activate?

Also can you tell me how th change to background color for the rendered image?

werwack
Great, thanks!!
The alpha transparency of the texture, which is clearly visible in the viewport, doesn't seem taken in account in the rendering. Is there something to activate?

It seems the default Decal Shader in H10 doesn't hook up the alpha channel from the Decal VOP… ops:
Instead of fixing it just replace the decal with a Basic Surface material from the gallery and use that to place the texture map.

I also noticed another issue with the Basic Surface. The specular is added on top of the surface after the opacity is factored in. This means specular on invisible surfaces. I can see why this choice was made as you want specular to contribute even if there is a wee bit of opacity but once opacity is zero, in this case you want spec to be eliminated.
If you want to fix this, dive in to the basic_surface vop network and:

1) Insert a Multiply VOP inbetween the addSpec Add VOP and the output1 Output VOP's Cf input.
2) Wire the output of the multiply2 Multiply VOP in to the last free input of the Multiply VOP you added.

With this hack the spec is now modulated by the opacity (and everything else making this an ugly hack).

werwack
Also can you tell me how th change to background color for the rendered image?

You can apply a background image of your preferred color to the Camera Object. Here are more steps…:

1) Select your camera object
2) from the Gear menu, select “Edit Rendering Parameters…”
3) type “background” in the Filter field for the Create Parameters Column.
This narrows down the list of parms.
4) in the Mantra 10.0 > View tab, select the following and add via the right arrow button:
Enable Background
Background Image
Scale Background To Fill Image
5) press Accept and now fetch your image in the Background Image parameter.

Now you can fetch a constant color background image and it could be just a single pixel if you have the Scale Background to Fill Image set to “on”.

Thanks a lot.

This scene is just a test I did to learn Houdini but it uses features, the material among others, I will use more extensively in the future.

It seems the default Decal Shader in H10 doesn't hook up the alpha channel from the Decal VOP… Embarassed

Whereas this seems to be a bug (will it be fixed in a next release?), I am not sure for the second one. Indeed there are cases were you want the specular to be visible only on the parts of the object where the diffuse is not 100% transparent (most of the cases), and sometimes, as for glass, you would like it to be visible on the whole object.

3dsMax has the second approach and requires a mask to be put in the specular channel.

If this shader had to be modified, it would be nice if it had a checkbox allowing both behavior.


Regarding the background color at render time, thank you for your trick. It is quite heavy though: not only it requires the image to be modified every time we want to change color, which is quite often during the setup phase, but it has to be done every time you need it (I think there is a way to let those parameters permanently on the camera, isn't it?), and on every computer for people in production.

As everything is node-based in Houdini, it would be really great to have the ability to plug a “background image” node into the input of Mantra node. This new node will have the parameters you mentioned above but also a color field for solid background and another one to receive any kind of image from the compositing part.

This would be so useful. Beside every other 3d package has a color background feature, it is at the base of rendering. Is there a reason Houdini does not?


Regards,


Werwack

Jeff,

while talking about materials, I have a small question regarding the basic_liquid shader. It comes with fluid simulations and gives good visual results.

Regarding the alpha though, it is not transparent… :?
In the alpha channel of the rendered images the whole fluid is opaque. It should be partially transparent where the background is visible through it, isn't it?

Thank you

werwack
Jeff,
Regarding the alpha though, it is not transparent… :?
In the alpha channel of the rendered images the whole fluid is opaque. It should be partially transparent where the background is visible through it, isn't it?

The Opacity is set to 1 to handle the case where primary samples are handled with MicroPolygon rendering. You don't want to compute secondary rays via refracted rays with the raytracer while the primary rays also get opacity less than one and shoot straight through to get double contribution.

As for the Alpha, I didn't write this shader so I do not know the reasoning behind setting Alpha to 1. I can only guess this is to aid in compositing as it will give you a solid hold-out for the water element.