Bake 2d particle position to texture

[papsphilip]

Sounds simple but i've never done this before. How can i bake particle positions into a texture sequence?

the point count is the same through out the animation

their position is always on XZ plane and 0 to 1 space

[ryew]

Have you tried the technique in the Entagma tutorial https://entagma.com/houdini-baking-point-attributes-to-textures/ ?

[papsphilip]

yeah i think this doesn't apply to this particular problem because they are rasterizing points in a grayscale texture, what i want is the actual xyz information in an exr sequence so that i can import it into Unity VFX graph.

i am using the vertex animation rop for now and it is exporting a really large texture. Each pixel is a point on a particular frame

this is probably the way to go although i would prefer if i had separate textures for each frame. Each pixel would have a color that corresponds to its xyz position for one frame.

i am not sure what the correct workflow is here

[ryew]

Ah, yes, a different use case here.  I'm sure someone in the Games subgroup here or on SideFXs forums can offer additional ideas or clarify the Houdini<->Unity best practices for this sort of thing

[papsphilip]

i managed to export a position map for all my particles  - one texture per frame - using a custom but simple solution.

i write each particle position as Cd on a grid of points. The grid point count must equal the particle count - if grid points are more its ok.

Then in COPS using a VopCopfilter i write the Cd from each grid point as one pixel value. So bottom left pixel 0,0 takes Cd from point 0 then continues right to the end of the row and then to the row above starting left to right.

 

i will upload my solution as soon as i find the time.

I am also thinking now maybe a python node would be the best solution of all. i will definitely try that as well - exporting point positions to an image straight from a python node

[mestela]

You can't use the labs vat particle export?

[papsphilip]

well that was my first choice but the texture for 500.000 or 1M particles over 480 frames is pretty huge and heavy. i wasn't sure this was the right workflow to be honest.

Also i am still not sure about the resulting precision of these textures from COPs. Even though i export 32bit float exr in my custom solution, when i go over the image in Houdini with the color sampler i can see the numbers are rounded. So a @P.x value of 0.625753 becomes 0.6258

since vat also uses COPs if i am not mistaken i was afraid of losing precision.