Hi Tim,
Here's a VEX example:
http://www.andynicholas.com/download/vex_trail_example.hip

I've kept it super simple to make it easy to expand on. It should be a great way to get familiar with VEX too.

Let me know if you have any questions.

A


On 02/03/2017 13:34, Tim Bolland wrote:

Thank you! Really cool :)


------------------------------------------------------------------------
*From:* softimage-boun...@listproc.autodesk.com <softimage-boun...@listproc.autodesk.com> on behalf of Christopher Crouzet <christopher.crou...@gmail.com>
*Sent:* 02 March 2017 13:25
*To:* Official Softimage Users Mailing List. https://groups.google.com/forum/#!forum/xsi_list
*Subject:* Re: [Houdini] Working with strands the Softimage way
If it can help, here's a basic scene showing one common approach for making strands: https://filebin.net/6ml27y3atb6qd7iq <https://filebin.net/6ml27y3atb6qd7iq>


On 2 March 2017 at 20:17, Tim Bolland <tim_boll...@hotmail.co.uk <mailto:tim_boll...@hotmail.co.uk>> wrote:

    Thank you Andy that's a really helpful summation, I'm going to
    give it a go :)



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    *From:* softimage-boun...@listproc.autodesk.com
    <mailto:softimage-boun...@listproc.autodesk.com>
    <softimage-boun...@listproc.autodesk.com
    <mailto:softimage-boun...@listproc.autodesk.com>> on behalf of
    Andy Nicholas <a...@andynicholas.com <mailto:a...@andynicholas.com>>
    *Sent:* 02 March 2017 13:12

    *To:* softimage@listproc.autodesk.com
    <mailto:softimage@listproc.autodesk.com>
    *Subject:* Re: [Houdini] Working with strands the Softimage way

    Just to confirm how I'm thinking about this, a strand in Houdini
    is typically made up of point positions, not points with arrays
    as attributes. You can manually add an attribute to each point
    position to say which strand it's part of, there's a node that
    generates lines that will then understand this?

    What I'm saying is that's something you can implement yourself.
    There are no nodes in Houdini that understand a point with a
    vector array is a strand, and no shaders that will do that
    automatically either. Again, you can build that yourself if you
    like, but it's quite advanced if you're going to be delving into
    procedural geometry shaders.

    Otherwise you can create polyline primitives and feed point IDs
    into it. This will generate a polygon line (polyline) between the
    vertices in the primitive, and in some ways this is just like the
    point[pointarray] technique.

    Yep. A polyline is nothing special. Just an unclosed polygon. As
    others have pointed out, you can apply attributes to the points to
    set things like width and color. Or you can use something like the
    PolyWire SOP to generate your own rendertime geometry.

    The key is how do you create these point clusters and the order.
    In ICE I would make strands using a build linearly interpolated
    array with two vectors feeding into it. I guess I could try and
    recreate this using vex/vops, and maybe that's what I'm after, I
    just need to find a way to manipulate all these points in the
    right order.

    Easiest way (assuming you already have some animated points) is to
    use the Trail SOP with it set to "Connect as Polygons", turn
    "Close rows" off, and set "Trail Length" to something like 10.
    Next stop after that is to take a look at the Resample SOP.
    Especially the "Treat Polygons As" parameter, as that'll let you
    create interpolated shapes to your trails which is kind handy.

    A




    On 02/03/2017 12:58, Tim Bolland wrote:

    That's a good point Andy, and in my mind this would make the most
    sense! But like you say maybe not the most supported.


    Just to confirm how I'm thinking about this, a strand in Houdini
    is typically made up of point positions, not points with arrays
    as attributes. You can manually add an attribute to each point
    position to say which strand it's part of, there's a node that
    generates lines that will then understand this?


    Otherwise you can create polyline primitives and feed point IDs
    into it. This will generate a polygon line (polyline) between the
    vertices in the primitive, and in some ways this is just like the
    point[pointarray] technique.


    The key is how do you create these point clusters and the order.
    In ICE I would make strands using a build linearly interpolated
    array with two vectors feeding into it. I guess I could try and
    recreate this using vex/vops, and maybe that's what I'm after, I
    just need to find a way to manipulate all these points in the
    right order.

    I'm rambling a bit here, but hopefully getting somewhere!

    Cheers,

    Tim

    ------------------------------------------------------------------------
    *From:* softimage-boun...@listproc.autodesk.com
    <mailto:softimage-boun...@listproc.autodesk.com>
    <softimage-boun...@listproc.autodesk.com>
    <mailto:softimage-boun...@listproc.autodesk.com> on behalf of
    Andy Nicholas <a...@andynicholas.com> <mailto:a...@andynicholas.com>
    *Sent:* 02 March 2017 12:27
    *To:* softimage@listproc.autodesk.com
    <mailto:softimage@listproc.autodesk.com>
    *Subject:* Re: [Houdini] Working with strands the Softimage way
    Hi Tim,
    Did you notice that you can do per-point array attributes in VEX?
    There's nothing stopping you setting up position vector arrays on
    each point, just like in ICE, and then using a Point Wrangle at
    the end to use that array to generate a polyline. The problem is
    that you then have to write all those handy ICE nodes like
    "Simulate Strands", etc. yourself.

    That's why generally, you're better off just trying to use
    polylines as a primitive as they're more supported by Houdini's
    other frameworks (e.g. wire solver) and constraints.

    A


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