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Hi Remo,
There is in fact a compound that does this included in the rebel pack, called create_particle_trails!
Rebel pack link: https://forums.autodesk.com/t5/bifrost-forum/rebel-pack-0-3-0-for-bifrost-2-1-0-0-released/td-p/9633...
The compound is called create_particle_trails.
Copy and pasting the in-app docs from that node (in the info tab if you select it):
Edit: just noticed some leftover text in the docs from an Arnold node under the "particles" input, oops. 😋 Hopefully it's self explanatory what you plug in there.
Creates strands trails behind particles.
If the particles have IDs (the point_id property), it can leave trails behind particles as they are emitted or die. This option is on particles solver settings as label_point_id.
Inputs
particles
Specifies the density property which Arnold will use to render. By default this is automatic and does not need to be specified manually. The automatic behavior is based on what the attached Arnold Standard Volume shader specifies as its density channel. However, if there is a different volume shader, or no shader is not applied, this allows it to be specified manually.
start_frame
Which frame is the start of the simulation. Will accumulate particle clouds starting from this frame.
num_frames
The length of the trails, in frames.
properties
Allows specifying custom user properties to copy to the strands. By default this is point_position and point_size - meaning the strands will have the sizes and postions of the particles they are emitted from.
Ahh, the answer is type wrangling. The short version is, you can right click on the min and max ports on this node and use "set value type" to select the type of random value you want.
For more detail and a more technical explanation, read on. I don't expect very many users to know the detail below, and certainly don't want people to have to know it, but I think it's nevertheless helpful to understand what's happening even if you don't ever create overloads of your own.
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If you create a random_value node, and dive in, you'll see that there's a hash called "jotun hash", which then converts the result of the hash into a float value.
If you go back outside again, right-click on "min", and set the type to Math::Float3, and then go back inside, you'll see a whole different implementation that creates three values from that hash. Creating a float3 random value is different from creating a float random value and a different graph does this, and having one node that represents multiple different graphs depending on types is called an "overload".
This interaction of setting the type on the port is what we mean by "type wrangling", where you can control the type system by creating values on ports. Values are like invisible value nodes, so just as plugging a float3 connection in there would cause the types in the graph to change, you can do it without a value node as well.
When you see "supported types" in the contextual "set value type" submenu, it's listing the different types a node has an overload for. "Suggested types", on the other hand, indicates that this port actually has the type "auto" and we've added hints. Lower level nodes tend to have overloads, and higher level nodes tend to have auto ports.
More info: https://help.autodesk.com/view/BIFROST/ENU/?guid=Bifrost_Common_build_a_graph_set_port_type_html
Hi jonah.
There is something that make create_particle_trails works only with nParticles and not with basic particles bifrost?
first image bifrost start no problem screenshot on frame 22 is ok.
Second image bifrost on frame 55 weird
Third image no problem any frame with nParticles.
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