Chris

I'm building a little video mixer with effects in jitter and although it uses so much CPU that it's hardly usable. Now some of it might be because it's my first jitter project and it might not be perfectly optimised. But I also found out that using the selector function in the jit.gen codebox makes it incredibly slow and I don't know why. I want to use it to select one of several effect functions, like this:

        effect1(vid1, var1, var2),

        effect2(vid1, var1, var2)

There are several of these in my code. But even if in all of them are set to fx_select == 0 (so that vid1 == vid1) playback gets extremely slow. If I comment them out it runs much faster. Why is this happening? Is there any better way to do this?

I'm building a little video mixer with effects in jitter and although it uses so much CPU that it's hardly usable. Now some of it might be because it's my first jitter project and it might not be perfectly optimised. But I also found out that using the selector function in the jit.gen codebox makes it incredibly slow and I don't know why. I want to use it to select one of several effect functions, like this:
vid1 = selector(fx_select,
		vid1,
		effect1(vid1, var1, var2),
		effect2(vid1, var1, var2)
);
There are several of these in my code. But even if in all of them are set to fx_select == 0 (so that vid1 == vid1) playback gets extremely slow. If I comment them out it runs much faster. Why is this happening? Is there any better way to do this?

selector-in-jit-gen-codebox-using-a-lot-of-cpu

I'm only just beginning to understand some of this but it looks like your definition of vid1 is generating a circular reference instead of an equivalence relation. Try renaming the variable that defines the selector. i.e. something other than vid1. Depending on the context, you send it directly out:

out1 = selector(fx_effect, vid1, effect1(vid1, var1, var2), effect2(vid1, var1, var2) );

I personally would use variables to keep track of things. The Gen object will compile the code anyway, so it shouldn't impact performance. iow...

Param fx_effect(0);
e1 = effect1(vid1, var1, var2);
e2 = effect2(vid1, var1, var2);
sel1 = selector(fx_effect, vid1, e1, e2);
out1 = sel1;


I'm only just beginning to understand some of this but it looks like your definition of vid1 is generating a circular reference instead of an equivalence relation.  Try renaming the variable that defines the selector.   i.e. something other than vid1.    Depending on the context, you send it directly out:

I personally would use variables to keep track of things.  The Gen object will compile the code anyway, so it shouldn't impact performance.    iow...

The re-use of variable names in the first post was ok, but Metamax's example is easier to understand. They are equivalent.

And that maybe helps show why it runs a lot of CPU -- all inputs to a selector will be computed, regardless of which input is currently chosen in the selector. This is just due to the way patching works in gen -- it is more like MSP than Max.

If you want to only compute one of the inputs (and thus potentially save on CPU), try using a if/else block statement.

if (fx_effect < 1) {
  out1 = vid1;
} else if (fx_effect < 2) {
  out1 = effect1(vid1, var1, var2);
} // etc...


I say *potentially* save on CPU, because sometimes using an if() can be *more* expensive than just computing both options. It may depend on the complexity of effect1(), effect2() etc.

And that maybe helps show why it runs a lot of CPU -- all inputs to a selector will be computed, regardless of which input is currently chosen in the selector. This is just due to the way patching works in gen -- it is more like MSP than Max.  

If you want to only compute one of the inputs (and thus potentially save on CPU), try using a if/else block statement. 

I say *potentially* save on CPU, because sometimes using an if() can be *more* expensive than just computing both options. It may depend on the complexity of effect1(), effect2() etc.


Graham, how does something like this compare in terms of performance?

out1 = (fx_effect==0)*vid1 + (fx_effect==1)*effect1(vid1, var1, var2) + (fx_effect==2)*effect2(vid1, var1, var2);

That will be pretty much similar to the selector case.

Ah, of course..  thank you.  That helps.


Selector in jit.gen codebox using a lot of CPU