Filter Forge - Script Optimization Tricks

Sphinx.

Filter Optimizer

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If you're concerned about the performance of your script, check out this page:
http://lua-users.org/wiki/OptimisationCodingTips

..Good stuff in there.

Please add your own findings to this thread, and feel free to post optimization problems smile:)

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Posted: June 16, 2010 3:30 am

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Vladimir Golovin
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Quote
Locals are faster than globals. See OptimisingUsingLocalVariables.

That's a good argument in favor of local which I used to dislike for aesthetic reasons.

Posted: June 16, 2010 5:05 am

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Sphinx.

Filter Optimizer

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Indeed! Also moving functions inside a main function (e.g. get_sample) seem to have impact. Dunno why that is, but its probably something related (less indexing or something)

Another thing I noticed is that the evaluation of conditionals with else parts can be slower than simply preinitializing the variable with the else part:

j = 0
if (i == true) then
j = 1
end

instead of

if (i == true) then
j = 1
else
j = 0
end

but of course it depends on the actual case: if the else part is a heavy piece of code performancewise, its not worth it.

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Posted: June 16, 2010 5:40 am

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Darrell Plank

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In assembler (well, at least the ancient 8086/88 assembler I used to write in), jumping takes longer than straight line code. If you write (the assembler equivalent of)

j = 0
if (i == true) then
j = 1
end

then you are making no jumps if i== true and even though you're setting j twice, that's way trumped by not making a jump and therefore faster. In the other example you're always making a jump.

This performance thing had to do with the pipeline in the old xx86 processors and unless LUA compiles directly to assembly (dunno, but I doubt it), then this isn't the direct reason but it may still be that in LUA jumps are expensive for whatever reason.

Darrell

Posted: July 1, 2010 12:40 am

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Sphinx.

Filter Optimizer

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This page show some interesting tests - I learned a few new tricks there smile:)

http://trac.caspring.org/wiki/LuaPerformance

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Posted: July 10, 2010 7:31 am

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Totte

Übernerd

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Very good info Sphinx!

- I never expected the Spanish inquisition

Posted: July 10, 2010 11:23 am

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Sphinx.

Filter Optimizer

Posts: 1344
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I started a new wiki page on the subject. Check it out and feel free to add stuff to it smile:)

Edit: The article covers very basic scripting concepts, so its a good read for scripting beginners smile:)

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Posted: November 15, 2010 5:55 am

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Vladimir Golovin
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Sphinx. wrote: I started a new wiki page on the subject. Check it out and feel free to add stuff to it

Just wanted to say that this is an excellent article!

Posted: November 24, 2010 2:16 pm

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Sphinx.

Filter Optimizer

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Thanks Vlad, I will be completing it soon - I'll probably split it up, so the examples are on a dedicated page.

If Egret or one of the programmers could take a quick look at it when they have a minute or two, that would be great - I'm not 100% sure about all the conclusions / assumptions I make.

Btw have you considered LuaJIT? I recall there was some problem with terminating endless loops, but perhaps you could make it optional (in the script settings add some sort of "Optimized (Unsafe)" option)

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Posted: November 25, 2010 2:18 am

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Sphinx.

Filter Optimizer

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Alright, the Scripting Tips and Tricks article is complete (for now).

It would be great with some feedback on it, specially regarding clarity: if certain parts need additional explanations etc, let me know.

Also if there are common operations you'd like to see covered, let me know.

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Posted: December 6, 2010 5:24 am

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James

James

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If i have 4 black and white gradients i noticed replacing them with scripted versions makes the render time go from 5.4 to about 10+ for some reason.

For the gradient though it is just -

function prepare()
end;
function get_sample(x, y)
return x, x, x, 1
end;

So i am wondering if there is even a good way to optimize that type of code since it is so simple. Maybe the default nodes are just a great deal more faster than Lua, since the default node has other controls as part of it though i was originally guessing the Lua version would be more optimized.

Posted: May 13, 2011 1:44 pm

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Sphinx.

Filter Optimizer

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Quote
Sphinx wrote "James wrote:" because direct Quote function does not work in Chrome If i have 4 black and white gradients i noticed replacing them with scripted versions makes the render time go from 5.4 to about 10+ for some reason.

I did some experiments regarding just that. You can read about it here:
http://www.filterforge.com/wiki/index..._script.22

Indeed there is a way to "optimize" that type of very simple scripts: don't script smile;)

The rule of thumb is simple: if you can easily construct the script equivalent just using a few native FF components, then its a better choice.

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Posted: May 17, 2011 1:44 am

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James

James

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Thanks, I was expecting that would be the answer.

Hopefully in the future this might change though, it would be great if the lua scripting could be made a bit faster so things like the simple gradient code i posted would rival or be faster than the standard node. smile:)

I just had a interesting idea -

http://www.filterforge.com/forum/read...ssage93321

Posted: May 17, 2011 10:19 am

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inujima

Posts: 107
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This document is helpful as well.

http://www.lua.org/gems/sample.pdf

Posted: May 17, 2012 2:02 pm

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Sphinx.

Filter Optimizer

Posts: 1344
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Good one Inujima!

Importance of localization:

Code
(page 17) ...For instance, the code for i = 1, 1000000 do local x = math.sin(i) end runs 30% slower than this one: local sin = math.sin for i = 1, 1000000 do local x = sin(i) end

And this one was new to me (initialization of table entries):

Code
(page 20) .. the next loop runs in 2.0 seconds: for i = 1, 1000000 do local a = {} a[1] = 1; a[2] = 2; a[3] = 3 end If we create the tables with the right size, we reduce the run time to 0.7 seconds: for i = 1, 1000000 do local a = {true, true, true} a[1] = 1; a[2] = 2; a[3] = 3 end