I’ve been thinking about state machines and cuing systems lately. Specifically, that there aren’t many good resources that I’ve found so far that talk new artist programmers through how to think about or wrestle with these ideas. Like many Touch programmers I’ve tried lots of different ways of thinking about this problem, and just today I saw someone post on the Facebook help group.
from the facebook help group:
Hi, i’m working arround Matthews AME394 Simple VJ-Setup Tutorial. No Questions, but how can i do nearly the same with different blending times between the moduls. I tried a lot with getting different values out of a table DAT into the length parameter of a timerCHOP. But cannot figur out the right steps to get my goal. Any helps? this i need in a theater situation with different scenes to blend one after another with scenebuttons or only one button and a countCHOP or something else.
This challenge is so very familiar, and while there are lots of ways to solve this problem sometimes the hardest part is having an idea of where to start. Today what I want to look at is just that – where do we start? This isn’t the best solution, or the only solution – it’s just a starting point solution. It’s a pass at the most basic parts of this equation to help us get started in thinking about what the real problems are, how we want to tackle them, and how we can go about exposes the real issues we need to solve for.
So where do we start? In this simple little state machine we’re going to start with a table full of states. For the sake of simplicity I’m going to keep this as simple as possible… though it might well uncover the more interesting and more challenging pieces that lie ahead.
I’m going to start with the idea that I’ve got a piece of content (an image or a movie) that I want to play. I want to apply some post process effects (in this case just black level and image inversion changes), and I want to have different transition times between these fixed states. Here the only transition I’m worrying about is one that goes from one chain of operations to another. I’m also going to stick with images for now.
So what do we need in our network to get started?!
We’re going to borrow from an idea that often gets used in these kinds of challenges, and we’re going to think of this as operating with two decks – an A deck, and a B deck. Our deck is essentially a chain of operators that allow for all of the possibilities that we might want to explore in our application. In this case I’m only working with a level TOP, but you can imagine that we might use all sorts of operations to make for interesting composition choices.
Alright, so we’re going to lay out a quick easy deck:
moviefilein > level > fit
Next we’re going to repeat this whole chain, then connect both of our fit TOPs to a cross TOP:
If you’re scratching your head at this fit TOP in line, that’s okay. For us, the fit TOP is going to act as our safety. This makes sure that no matter what the resolution of the incoming file might be, that we always make sure that both decks have matching proportions. We’d probably want a little more thought in how this would work for an event or a show, but for now this is enough to help ensure that don’t experience any unexpected resolution shifts during our transitions.
Next we’re going to add a simple tweening system to our network to control how we blend between states. In this case I’m going to use a constant, a speed, and a null. I need to make sure that my speed is set to clamp, and that my min and max values are 0 and 1 respectively. Right now I only have two different decks, so I don’t want to go any higher that 1 or any lower than 0.
Now we’re cooking with propane! So where do we go next?
some simple cues
In this simple examination of this challenge I’m going to use a table to store our cues. In a larger system I’d probably use python storage (which is really a dictionary), but for the sake of keeping it simple let’s start with just a table. Our simple cues are organized above, and we can put all of those values into a table DAT. You’ll notice that for now I’m only worrying about file name and not path – all of these files come from the same directory so we can treat them mostly the same way. We’ll also notice that I’m thinking of my transition times in terms of seconds. All of this can, of course, be much more complicated. The trick is to sort out a very simple example first to identify pressure points and challenges before you dig yourself into a hole.
Okay, let’s add a table DAT to our network and copy all over our cues over.
Now that we have all of our pieces organized it is time to think through the logic of how we make this all work. For now let’s use a button, a count CHOP, and a CHOP Execute DAT. We need to make sure our button is set to be momentary, and we also need to make sure our count CHOP is set to loop – starting at 1 and ending at 6. That matches our row indices from our table DAT.
This is great Matt, but why python?
Well, we could do a lot of this with a complex set of CHOPs and selects but these kinds of states tend to be better handled, logically at least, through written code. Python will let us explicitly describe exactly what happens, and in what order those things happen. That’s no small thing, and while it might be a little rocky to wrap your head around using Python in Touch at first, it’s well worth it in the end. So what do we write in our CHOP Execute?
a little bit of logic | python
Uhhhhhhh… wait. What?
Okay. First off we just define a set of variables that we’re going to use. This makes our code a little easier to write, and easier to read. Next all of the action really happens in our onValueChange function.
We’re going to do all of this in a little logical if statement. If this thing, do that thing… in all the other cases, do something else.
First we check to see what our deck position is… which means that we check to see which output we’re currently seeing more of. If our cross TOP’s index is greater that 0.5 we know that we’re closer to 1, which also means we’re seeing more of deck B than deck A. That means that we want to make changes in deck A before we start transitioning. First we change our file, change all of our settings, then finally set a value in our constant CHOP. But why 1 / that value? And why multiplied by -1?
A default network runs at 60 fps. A speed CHOP fed by a constant with a value of 1 will rise a count of 1 over 60 frames. Said another way, an input value of 1 to our speed in a default network will increase by a count of one every second. If we divide that number in half we go twice as slow. A value of 0.5 will increase by a count of 1 every 2 seconds. 1 / our table value will let us think in seconds rather than in fractions while we’re writing our cues. Yeah, but what about being multiplied by -1?! Well, if we want to get back to the 0 index in our cross TOP we need a negative value feeding our speed CHOP. Multiplying by -1 here means that we don’t need to think about the order of cues in our table DAT, and instead our bits of Python will keep us on the rails. Our else statement does all of the same things, but to our B deck. It also uses a positive value to feed our speed CHOP – since we need an increasing value.
There you have it, a simple cuing system.
This is great Matt, but what if I want to tween settings on that level TOP? Or any other set of complicated things?! Well, I’d be that at this point you’ve got enough to get you started. You might use a column to indicate if you’re transitioning to a totally new cue or just to new values in the same source image. You could also choose to put your parameter values in CHOPs instead so you could manipulate them with other CHOPs before exporting them to your decks.
What if I don’t want linear transitions?! A speed is just a linear ramp! That’s okay. You might choose to use a lookup CHOP and a more complicated curve. You could even make several types of curves with animation COMPs and switch between them. Or you could use a lag CHOP to change your attack and release slopes. Or you could use a trigger CHOP, or a fileter CHOP. There are lots of ways to shape curves with math, now it’s up to you to figure out exactly what you’re after.