[Joe Laude]

I tried a while loop and it does indeed work. It slows down as it progresses, like you said, as each frame adds one more loop it has to go through each time.

Thanks.

[Joe Laude]

So how would you do that?

[Joe Laude]

Like I’d expect, so you can understand my confusion 🙂 Could it be a version thing? I’m using AE 9.0 on OS X Tiger 10.4.11 on this workstation. All the other machines I use have the most recent updates of AE and Leopard, so maybe it’s a bug, unique to this combination or something. Weird.

[Joe Laude]

This is the 4-line expression I’m using now in it’s entirety, and it’s not giving me errors:

p=comp(“Pre-comp 2”).layer(“MovingPlate”).transform.position;
x=p[0]+transform.position[0];
y=p[1]+transform.position[1];
[x,y];

As I’m sure you can tell, it’s just meant to parent the position of a layer in the main comp to another layer within a pre-comp, and allow an offset.

To check that the array, p, was receiving the correct values from “Pre-comp 2,” I added “[p[0],p[1];” between lines 1 and 2, and commented out the remaining 3 lines. Like this:

p=comp(“Pre-comp 2”).layer(“MovingPlate”).transform.position;
[p[0],p[1]];
//x=p[0]+transform.position[0];
//y=p[1]+transform.position[1];
//[x,y];

That gave me an error. At first, I was wondering what I did wrong (whether [p[0],p[1]] was valid syntax-wise, and questioning my memory as to whether this was the correct way to comment in AE). I deleted those commented lines, like so:

p=comp(“Pre-comp 2”).layer(“MovingPlate”).transform.position;
[p[0],p[1]];

That worked, so I knew there wasn’t a problem with the code. I proceeded to check the manual about comments, tried commenting both ways, with “//” and “/*” and both gave me different errors. I can see why commenting out the whole expression would make AE mad, but not 3 lines when the rest works on it’s own.

Due to that pre-comp and the main comp starting on different frames, these values were off from what I was expecting. I didn’t catch that right away, so that’s why I checked the values going into the expression first. It’s working, so again, it’s not a big deal. This strange behavior simply tripped my curiosity.

[Joe Laude]

Maybe I should emphasize that I did add in a line that did get the portion above it to resolve to a value, then I commented out the rest of it. Then I got errors, and I didn’t have errors before. I removed the commented lines, leaving the rest unchanged, and it worked without error. To me, After Effects should look at an expression with commented lines and the same expression with those commented lines completely omitted as the exact same thing, and one was giving me errors while the other was not. That’s what I mean.

[Joe Laude]

Maybe I’m not be getting the problem across. If you follow what I was saying before, the code worked without the commented part. That’s what was weird. I wasn’t commenting out a vital portion–the expression worked perfectly with the commented out part completely deleted from the expression, so it worked.

I was trying to leave that part to check that the first half of my expression was pulling the right values from the pre-comp. It was, but I had to actually cut the following portions of the expression to check, and then paste them back in, where a comment would have worked.

[Joe Laude]

It doesn’t seem like it should work that way, though. I was commenting out part of the script to make sure the other part was actually working properly without deleting it, not just to “turn off” the expression. I know about the button, I would have used that. It’s that it’s still reading what’s inside the comment tags, and furthermore, it’s reading errors where there are none.

I guess it doesn’t totally defeat the purpose of the comment tags, since you can still write notes for yourself and others, but don’t people use this method all the time? Commenting-out lines of code in order to use portions without deleting the rest? Why doesn’t AE just ignore anything inside comment tags?

Not a big deal, I’m just curious if maybe there’s a reason it is this way.

[Joe Laude]

The commented out version:

/* p=comp(“Pre-comp 2”).layer(“MovingPlate”).transform.position;
x=p[0]+transform.position[0];
y=p[1]+transform.position[1];
[x,y]; */

Gives this error: “Undefined value used in expression. Could be an out of range array subscript? Expression disabled. Error occurred at line 0.”

And commenting each line with “//” tags gives this error: “No matching closing brace found. Expression disabled. Error occurred at line 1.”

Removing all comment tags gives no error at all, and the expression works.

When I add “[p[0],p[1]];” after the first line, and comment out the last 3 lines with “//” tags, I also get the “No matching closing brace found” error, but then completely deleting those 3 lines, again, works fine.

Does that make sense to you? The expressions work, so it’s not like I’m stuck. I’m just kind of baffled by this strange behavior.

[Joe Laude]

Google “Trapcode.” Those blobs at the end look like they could have been done with Particular, and the swirls look like they were done with 3D Stroke, both Trapcode plug-ins.

[Joe Laude]

Sort of depends on what you want your result to look like. Todd is right, it always looks better when it’s shot practically, but if you’re in a pinch and you need to simulate something, there are many ways to do it, and which one you use depends on what you want the result to look like.

Trapcode Form is a really cool plug-in that can make some firey-looking effects (there’s an example project on Trapcode’s website somewhere for flaming text and it really looks like a gas-burning stove with letters over it), and Particular is good with making sparks, explosions and/or smoke (and I’ve recently discovered it can make some decent liquid spurting effects), but it ultimately depends on what you want it to look like in the end.

But to reiterate what Todd said one more time… shooting video of an actual flame will always look the most realistic because it is in fact real.