Houdini python for loop

How to get information about the current loop. Debugging and testing loops. Normally, Houdini processes the nodes in a geometry network from top to bottom, feeding the output of each node into the input of the next node, down to the node with the display or render flag.

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You want to process the input geometry over and over again. For example, you might want to add multiple layers of noise, or create complex procedural geometry by extruding all faces multiple times. You want to process each piece of the input geometry. You want to process one geometry using each piece of another geometry. The classic example of this is the "Swiss cheese problem": you want to loop over each sphere in the set of air bubbles and subtract it from a block of cheese.

The tool will create a Block Begin and Block End node wired together. The Block Begin has the Method parameter set to "Fetch feedback", meaning it will start each loop after the first with the output of the previous loop. Select the Block End node and set the Iterations parameter to the number of times you want the loop to run. You should probably start with just 1 or 2 iterations at first until you know the loop is working they way you want. The point of this type of loop is that the output of one loop becomes the input for the next loops, so any geometry you create in the loop will accumulate.

If all you want is to apply the same nodes once to multiple copies, you want the Copy node.

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A "piece" is usually defined as the primitives that have the same value of the piece or name attribute. Several tool such as Shatter create this type of partition attribute for you. The Block Begin has the Method parameter set to "Fetch piece", meaning it will start each loop with a different piece of the input. This will usually be primitives.

In this example, we loop over the pieces of a shattered torus and apply Mountain to each one individually. A loop can have more than one Block Begin node. So, for example, one branch of the network will get its input piecewise and another branch will be simple repetition accumulating the result of using the pieces. The classic example of this type of loop is making Swiss cheese: use simple repetition to accumulate the results of processing one input geometry the cheese block by looping over pieces from a second input geometry the air bubbles.

Create another Block Begin node. Set the Block path parameter to the Block End of the existing loop. You can use the node chooser button next to the parameter, or drag the Block End from the network editor onto the parameter in the parameter editor. The first Block Begin is a simple repetition that takes the VDB "cheese block" as input and accumulates the changes inside the loop.

Houdini - Ответ - Блоки Foreach

The second Block Begin is a "Fetch Piece" that takes the "air bubbles" as input and loops over each primitive sphere. Under it we turn the sphere into a VDB. Sometimes you need the current loop, or the current piece number, in an expression on one of the nodes in the loop. You can get this information with a "Fetch metadata" Block Begin node.

houdini python for loop

Select the Block Begin node. In the parameter editor, click Create Meta Import Node. This button adds a second Block Begin node to the side of the existing one.

This node is set up to generate an empty geometry with some detail attributes. The expected total number of iterations, taking into account the Max Iterations and Single Pass parameters on the Block End.

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In piece-wise loops, this is the current value of the attribute, for example the piece integer or name string or the current point or primitive number if there is no attribute. In simple repetition, this is an integer version of value.While our script worked upon launching Houdini, it did not appear to run when creating or opening an existing. This is a bit dense so grab your Yoo-Hoo. We did some refactoring of our script so everything is looking spiffy.

However, the issue is the script only works when we start a new Houdini session. If you recall, this is because Houdini executes two scripts. The first script, The second script, Your initial thoughts to solving this problem might have been to just copy over the code from to or just duplicating the file.

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Once for each individual script execution. If you tried opening an existing scene, the nodes get created even if they already exist. Not only that, we need to address the duplicate nodes upon launching Houdini.

Enter globbing. Globbing is a term used in programming circles, especially Unix environments, that defines the use of wildcard characters for pathname expansion. First, what is a wildcard character?

houdini python for loop

There are many more. This subject goes deep so we will leave at that here. Since the asterisk matches one or more characters, it globs anything following the letter p in myGroup.

Sort of like Pac-man. If you had a few hundred groups, you can see how this becomes extremely handy. Have a look at the following example done in Hscript.I mean, we know that in our trusty VEX Wrangles, we write a line of code, click on that little thingamajig and suddenly we have our custom parameter.

A little different than in a Wrangle but not painful. All you do in order to create spare parameters in a Wrangle is to make a call to the ch function and assign that to a variable and your are golden. However, if you have some Python chops, why not leverage them? The first thing you need to do is create the spare parameter via the Parameter Interface window. Once in the Parameter Interface window, drag over your data types you intend to use and set up your parameter name and label.

Remember what you are naming the name parameter because that will be important later. This is the internal name Houdini uses to access the data. The Label is just for the UI. Before you can use your new parameters you need to hook them up with a bit of Python code. You are doing the opposite of how you would do this in a Wrangle.

Except for the icon thingamajig. In order to use the spare parameters we need to use a bit of Python code. The line of code that does the magic is node. Let me explain this a bit more. In Python you use evalParm path.

This function takes an absolute or relative path.

houdini python for loop

This just means the path to the parameter value you are hooking up. It will return an intfloator string depending on what type of parameter you feed it. Remember the name you gave your parameter back in the Parameter Interface window?

However, this could be any other parameter that is already available. So you can use this function to drive the value of a parameter from another node. It returns the node containing the expression.Arrays can be really useful if you want to store and manipulate list of items usually items of the same type.

This allows an entire list to be referenced by a single variable array. Array is defined similarly to any other attribute, distinguished by square brackets. These are literal arrays you literally type in array elements.

If you want to rather generate an array procedurallythere is a simple example of how to do it:. This code will loop 10 times in detail mode, appending a current loop number to the array called myarray at each iteration. The array will look like this: [ 0,1,2,3,4,5,6,7,8,9 ], giving you a list of all existing point numbers. This is a vector array. The result will look like this: [ 1. For arrays, there are several mostly straightforward functions for manipulating arrays: adding or removing elements, sorting, slicing, indexing and iterating over array elements.

Check docs to learn about them. It is imported as a local point array and iterated over in foreach loop. Now a bit more practical example that may come in handy when dealing with texture variations:.

Python for Loop Statements

Put down attribwrangle SOP and make it run over primitives. Then it will randomly assign one of the listed textures to each primitive. The hip file can be downloaded here. Put found points into an array called pts. Then set color for each array element. I needed to extract tokens from it and use it to drive stuff in my Houdini network.

Here is how i went about it, using arrays:. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. Search for: Close.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Is there? EDIT: Some suggested I use xrange instead of range since range returns a list while xrange returns an iterator. But in Python 3 which I happen to use range returns an iterator and xrange doesn't exist. So you can do the following.

Note for Python 3 users: There are no separate range and xrange functions in Python 3, there is just rangewhich follows the design of Python 2's xrange. This works on basically everything that has a defined order, including xrange objects and lists. To reverse a string without using reversed or []try something like:. Learn more. How to loop backwards in python? Asked 9 years, 8 months ago. Active 1 year, 7 months ago. Viewed k times. Peace out.

Feb 17 at Active Oldest Votes. So, xrange 10, 0, -1 Note for Python 3 users: There are no separate range and xrange functions in Python 3, there is just rangewhich follows the design of Python 2's xrange. ShadowRanger Chinmay Kanchi Chinmay Kanchi Since this question is about iteration please use xrange instead of range doesn't matter much for small ranges but starts mattering for large ones.

I used range simply because the OP did. Also, in Python 3. Chinmay, why not use your answer as a way of showing best practices to the OP? No reason not to suggest using xrange. Aware that reversed function is returning a list. So reversed range will return new list with items.

Odomontois, no, it doesn't. It returns an iterator. It returns result of obj.A TOPs Feedback Loop block lets you run a sequence of serially executed steps for multiple iterations. A TOP network already behaves somewhat like a parallel loop: it runs as many work items at the same time as possible based on the scheduler settings.

houdini python for loop

Sometimes, however, you want to run a series of steps serially rather than in parallel, and use the output of previous work items as input for subsequent work items. For simple simulations this is already handled by the ROP Fetch node, which is able to create batches that run as a single job, one frame at a time. In a feedback loop block, the network runs the work items node by node, with later work items depending on the previous work items, forcing them to execute serially. Then when all work in an iteration is done, if the block specifies more than one iteration, it loops back to the start and executes the next loop.

Depending on the settings, a feedback loop block can also run multiple serial loops in parallel. For example, imagine an RBD simulation where a jar is being filled with marbles, one handful at a time. The entire process could be run as a single simulation, however marbles at the bottom of the jar might become unstable and the numbered of simulated objects would keep growing.

One way to manage this is to run the RBD simulation for the first handful of marbles and use its results as a static object in the second simulation. The result of the second sim and first sim combined would be static objects in the third sim, and so on.

Feedback loops are also used to implement command server chainswhere the commands must be sent to the server sequentially, one at a time. The default is to run the number of iterations specified in the Iterations parameter. If the Begin node has upstream items, the loop runs iterations times for each incoming item. For example, you might have a loop that iteratively builds up a scene over the certain number of iterations such as the "dropping marbles in a jar" example from the overview.

You could then repeat the loop for each item generated by a Wedge node you wire into the Begin node. If the Begin node has static work items, you can turn on Iterations from upstream items. This sets the number of iterations to be the number of upstream items. This repeats the sequential series of steps within the block once for each input item.

For example, you could use a File Pattern node to list all of the files in a directory, and a loop block to iterate over the files and append the contents to a temporary file.The python console in Houdini is a live command line, which is great for some things, but doesn't allow you to enter multi-line code easily.

Maya's script editor allows this, I wanted a similar thing in Houdini. The python SOP looks like its the answer, but don't be fooled. Its the python equivalent of a point wrangle, its designed to process geometry, not do general node or UI fiddling which is really what you'd want python for. With the help of Luke Gravett, here's a way to make something akin to maya's python script editor. This is version 2 of such a thing, it's just a null with a text editor and a button to execute the code.

From the node get its geometry, then its point attributes, then the short names of those attributes. Do this, and what you drag will be converted into the python text equivalent. This works for nodes, parameters, shelf buttons, most parts of the UI. Parent in houdini means the container; ie if you have a subnet1, and inside is box1, if you ask box1 for its parent, its subnet1.

If you have box1 connected to mountain1, and ask mountain1 for its inputs, you'll get box1 as a list. Assumes a lot; that the image sequence within each folder is of the same name, and the parent folder only contains subfolders with images, no error checking is done, may contain traces of peanut etc Most rops both for rendering and for saving geometry have the main 'save to disk' button named 'execute', and to press a button you call pressbutton.

Hence you can do this:. Contrived example, more for the workflow than anything. Say you want to use python to generate the image path for a mantra rop.

Python in Houdini

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