Making Streaks cast shadows

[Tom]

Hello-

I know that the particles listed as "Blobbies, Hair, Sprites,and Fluids" all have a "Cast Shadows" selection in their properties menu.

I believe "Streaks" are able to cast shadows IF certain things are done. I believe it must be a Klieg light with ray traced shadows. There are also other steps one can take but the correct order escapes me at the moment.

 

Does anyone know how to make Streaks "Cast Shadows"?

 

Thanks!

Tom

[robcat2075]

I am surprised to only notice now that streaks can't cast shadows! I presumed they had that option but they don't.

If I had to have streaks cast shadows I would do it with compositing...

• Make a render with everything set to black except the streaks set to white, shot from the vantage point of the light. This will look like white particles on black.
• apply that render to the light to project it on the scene. Render from the regular camera view with all objects to white, turn off streaks, turn off all other lights. This will look like white lights crawling on otherwise unlit surfaces. This is your streak shadow buffer.
• Render the scene normally to OpenEXR format and composite the streak shadow buffer with the OpenEXR shadow buffer to combine the shadow information. This compositing could be done in an A:M Composite project or in something like After Effects.

This is sort of how Z-buffered shadows work anyway

 

However it is probably easier to fashion a small sprite that looks like a streak and use Sprites instead 😃

[Tom]

Thanks for the reply Rob!

What is interesting is I was fooling around with trying to get streaks to cast shadows and I clicked on the little red "X"  to opened up the drivers connected to the Streaks in the Choreography window and all of a sudden it looked like it was giving me the option to choose, "cast shadows" in the properties window...but when I went back to look for it, it had disappeared and I was unable to find it again...so maybe I was hallucinating or something.

I will remember your method for the future but it might be a nice feature to have streaks cat shadows like the other particles.

[robcat2075]

I used to have a hallucination where I saw bugs out of the corner of my eye but it went away before I saw a Cast Shadow option.

[Guest Ha..]

1u11Can lWhat do you think are the strengths and weaknesses of both streaks and sprites?

[Tom]

Rob-

I signed into the forums on my phone and didn't remember my user name password so it listed me as the guest... shown above...

however, I would be interested in your personal opinion of when to use streaks and when to use sprites? What is your view of their strengths and weaknesses?

[robcat2075]

I was hoping for the mysterious stranger!

Differences...

Sprites have many more possibilities in the properties.

Do streaks render faster? Or use less memory?

You should try setting up a test to compare the two. You'd probably have to set the emission rates very high to see a difference, like 100,000.

[Tom]

very good...thanks for the reply!

[robcat2075]

I thought of a significant difference...

Sprite  "size" is always a uniform scaling of their sprite image. They never get fat or skinny.

Streaks have a "thickness" but instead of a length they have a "duration". The length of a streak depends on how fast it is traveling. Faster streaks are longer and if they stop moving they disappear entirely.

That would be the major quality that neither can imitate of the other.

 

[Tom]

great insight!

 

BTW- I dropped a note to Steffen and asked if there was a way to make Streaks cast shadows...will post his reply if there is.