Scripting the Image Name attribute?

I've got a problem. I wan't to script the "Image Name" attribute in a file node to select random image cycles for sprites (not frame extension, which is already scripted).

First of all there is no expression option in the image name attribute. But I tried something like this in the particle runtime exp:

setAttr file1.ImageName = $someCreationExpValue;

I was hoping maybe the hardware renderer would run the runtime expression at the time of rendering each particle, so that I could cheat it, but (of course) it didn't. So it seems it must be done some other way. Does anyone know how?

how about having one long sequence with different image seuences in a row, all the same base name and succeeding numbering?

like that scripting the frame number would be enough..

btw:
setAttr does not work with = .. check the docs for the use of it.

cheers

alexx

Probably the best way to do this is by having a series of textures in an array and then using the rand command to look up the array index randomly:

int $i = `rand 0 100`;
setAttr file1.ImageName myArray[$i];

Unfortunately, David's answer doesn't work if you're doing hardware-textured particle sprites, only if you're treating each sprite as a separate geometry object.

If you look in the Maya documentation under the tempting heading Dynamics : Advanced Particle Topics : Assigning a different image sequence to each sprite you'll see that all they give you is a way to start each sprite on a different frame of one image sequence.

So here's the trick: let's assume your sprite loops are all the same length, say 1000 frames. What you want to do is:

1) Make a SINGLE series of images that contain all of your loops end-to-end. For example, frames 0-999 are the first loop, 1000 - 1999 are the second, and so on.

1) Add the dynamic attribute spriteNumPP to your particles

2) In your creation expression, set the initial value of spriteNumPP like this:

spriteNumPP = rand(0,19) * 1000;
// in this example, we're assuming 20 loops

4) In the runtime expression, update spriteNumPP each frame:

spriteNumPP = (spriteNumPP + 1) % 1000;

This will now pick a random loop for each particle out of the end-to-end sequence of loops that you've put together.

It's a shame there's no better way to do this, but without per-particle filenames (which sprites don't support) this is about the best you can do.

If I were going to do this in production I would consider writing a short install script that would let me take a library full of sprite loops and compile the end-to-end sequence of loops on the fly whenever I made changes. It would use a little more disk space but would be easier to manage that way.

-- Mark

Ahh..Mark..my old nemesis....

I was reading too quickly and thought it was to randomly assign a texture for a material.

I agree that writing a management tool is the way to go though.

Nemesis? I hope not!

-- Mark

sarcasm. Tis a wonderful thing.

Thank you all for replying! Mark: Super! I've got it all working now.

One little thing: spriteNumPP = (spriteNumPP + 1) % 1000;

This does not allow the values to go above 1000. 2900 becomes 900, 1800 becomes 800. That's not a problem, my sprites are driven by a very different expression. I know it's not supposed to do this, but I'm sure you've got a good answer to it

Oops slight mistake, as you noted:

The thing to do is make a second per-particle attribute. You can use one of the userScalar<n>PP attributes. Then, you do something like this:

// creation expression
spriteNumPP = rand(0,19) * 1000;
userScalar1PP = spriteNumPP;

// runtime expression
spriteNumPP = (spriteNumPP + 1) % 1000 + userScalar1PP;

This should fix your problem. Now, each particle will cycle through the range of frames for its particular sprite loop.

-- Mark

Thank you for clearing that up Mark.



Just for future reference. One would have to do this in the creation expression:

// select random loop
int $randLoop = rand (0,19);
$randLoop *= 1000;
userScalar1PP = $randLoop;

// select random sprite in loop
int $randSprite = rand (0,1000);
spriteNumPP = $randLoop + $randSprite ;

Runtime is ok.

mmi: sorry, you hadn't made it clear that you wanted the particles with the same loop to be out of phase with each other. I could imagine that going either way depending on what you're trying to do, but I can see why in most cases you'd want it that way.

-- Mark

Yes, you're right. I didn't mean to correct you, just show what I needed to do for my specific task

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