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Cart #userdata_tunnel-0 | 2024-03-15 | Embed ▽ | License: CC4-BY-NC-SA
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Here's a simple tunnel effect I did to test out doing pixel effects with userdata. Not super inspired, but it does run at 60fps at full resolution!

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Cart #userdata_tunnel_moving_center-0 | 2024-03-15 | Embed ▽ | License: CC4-BY-NC-SA
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Added some more motion to the effect using strided userdata operations. My intuition was that this change should effectively be free from a performance perspective, but that hasn't worked out for a few reasons:

  1. I can't get userdata ops to work as I expect when u0 and u2 are not the same object.
  2. I'm not sure stride parameters allow you to "cut out" part of u0? It looks to me like you always have to iterate over each element of u0.
  3. Strided ops seem slow - the strided copies here seem to be ~3x the cost of non-strided copies.

So as a result this cart only runs at 20fps, unlike the original, which runs at 60fps.

Thank you for sharing this. I would also have expected that this change would only have the overhead of a 3 strided copies. It seems that since you shared this strided copies are now broken for non "u8"-typed matrices, and the 1st element gets broadcasted throughout.

This cart successfully exercises strided copies for userdata matrices of type "u8":

Cart #userdata_scroller_test_1-0 | 2025-09-10 | Embed ▽ | License: CC4-BY-NC-SA

While this cart fails trying to do the same with userdata matrices of type "u32" (as of Picotron 0.2.0h3):

Cart #userdata_scroller_test_2-0 | 2025-09-10 | Embed ▽ | License: CC4-BY-NC-SA
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Thanks @Maca -- this is fixed for 0.2.0i

It was a bug handling a legacy form of :copy that is no longer needed with the introduction of ":take" ~ a disambiguation suggested by @luchak to avoid exactly this kind of problem! (good idea, poor execution on my part)

Thank you so much! actually :take is much more convenient for what I was meaning to ultimately do with usermem than copy. I was reading an old version of the usermem documentation and didn't even know about :take or the :copy overload. Thanks to @luchak as well for having suggested it!



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