Post by Screwtapello in New Tutorial: All About Transitions

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The tip about “prefer pre-shuffled lookup tables to actually calling random[]” is a good one. For the “Screen Melt Transitions” deck (thanks for the shout-out!) I tried to generate random numbers at the beginning of each transition, and as a result I had to lower the transition quality to fit within Decker’s calculation limits.

I do like the way that the transition looks a little different each time you see it, but maybe I should try randomly generating numbers at module-initialisation time rather than on the first frame of the transition. I could even add a reseed[] method to call outside the transition effect, to generate a new pattern for the next transition.

Internet Janitor11 days ago(+1)

You might also find the new sys.ops performance counter in v1.64 handy; rearranging expressions to do as much work as possible in a "vector context" rather than a "scalar context" can have a big impact on how many ops and how much wall-clock time is consumed by a hot loop. The "performance" example on the lil playground offers a worked example of micro-benchmarking with this tool.

Screwtapello6 days ago(+1)

Thanks for the tip! I did indeed move to generating the patterns at startup, rather than on the first frame of each transition, and that helped.

I also optimised the inner drawing loop from:

each pos in xs join ys
 # grab the strip from the old screen, starting at the top
 strip:a.copy[pos[0],0 stripwidth,stripheight]
 # Draw the strip at the target position
 c.paste[strip pos]
end

…down to this:

stripsize:stripwidth,stripheight
topfactor:1,0 # pos*topfactor = pos[0],0
paste:c.paste
copy:a.copy

each pos in xs join ys
 paste[copy[pos*topfactor stripsize] pos]
end

For 256 strips, that brought the total op count from ~6000 down to ~4000, so I could paint 512 strips and stay within the operation quota for a transition frame. Of course, then I start pushing against lower-level performance limits… but I’m happy to stop there.

itch.io

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