This article originally appeared in Digital Production 02 : 2019.
The software packages Houdini from SideFX and ZBrush from Pixologic both have strengths and weaknesses in the area of modelling. If both software packages are available in a pipeline within a production start-up, it is obvious that they should be linked together to maximise flexibility in the design of 3D models. For 19 US dollars before tax, the idea becomes reality and users can exchange 3D models between the packages on-the-fly and work flexibly until the desired result is achieved.
The idea behind connecting Houdini with ZBrush comes from Ale xey Vanzhula, who created the plug-in called – Z for Houdini. The plug-in is currently in version 1.1 and is under constant revision with the aim of increasing its functionality. The principle behind the Z for Houdini plug-in is relatively simple. There are two software packages, both of which have strengths and weaknesses. However, in the area of character modelling and animation and, for example, 3D photogrammetry for the creation of game assets, it makes sense to bundle the potential of both software solutions in order to achieve maximum performance and remain flexible within the scope of the respective tool selection.
The plug-in therefore takes care of providing the current geometry in the active software package. An example scenario can be used to illustrate this. Scenario one would be a geometry created in Houdini. The creation of a 3D character based on 3D photogrammetry would make sense, also because Capturing Reality can also be used as a plug-in version in Houdini. SideFX offers a capturing reality plug-in that is available free of charge as a beta. All that is required is an active or rather paid licence. However, demo licences and the Steam licence are not compatible. The promo licence is available at a price of 99 euros for 3 months. Once an image sequence has been read in and a mesh and vertex colours have been generated from a point cloud, you can take a look at Z for Houdini.
Reorganisation of polygons
Once Z for Houdini has been successfully installed, users can open the new shelf called Z. It contains a total of ten functions at the time of testing. The main tool is called Z Edit. If Houdini geometry is to be changed in ZBrush, the function must be confirmed. Z Edit works either at OBJ or SOP level. In the latter case, the geometry of the selected SOP node is transferred to ZBrush. The same procedure applies at OBJ level. The geometry of the selected node is transferred. If no OBJ node is selected, all OBJ nodes or their geometry are transferred.
When the editing process in ZBrush is complete, it is sufficient for users to switch the programme window, for example by pressing the Alt-Tab key combination. The geometry in Houdini is automatically updated to the current version from ZBrush. The update is carried out without the user having to do anything, without numerous clicks or the specification of paths. The update in Houdini is noticeable at SOP level in that additional nodes have been created. One of these is the SOPNode switch, which makes it possible to compare the current geometry with the last one and, of course, to delete nodes. New OBJ nodes are created at the OBJ level and the nodes with the older geometry are deleted. At this point, only the classic Ctrl Z remains for a jump back.
The steps can be carried out as often as necessary to complete the geometry in a way that is favourable to the modelling. Before each change, only the Z-Edit function needs to be activated. Once the 3D geometry has been created based on the photo series and exported to ZBrush, users can easily perform the retopology pass in ZBrush and make the geometry available for further processing in Houdini, for example for the game asset pipeline and the baking of vertex colours from the original to the UV layout of the optimised mesh. The developer has made work a little easier for users here, as the ZRemesher can be activated directly from Houdini using the function of the same name.
Z for Houdini enables data to be exchanged from more than just one direction. The Z Import function is used to transfer the current geometry from ZBrush to Houdini. A geometry is created in Houdini and the Z-Edit function is called automatically. If a ZBrush file has several sub tools, a geo node is created for each sub tool. It is interesting to note that the textures created in ZBrush in polypaint mode are also transferred to Houdini. The information about the colouring is stored in Houdini as cd point attributes, which can therefore be easily read out.
Cleaning up the newly created nodes and nodes that are no longer required does not have to be done manually. The SOP history is cleaned up by clicking on the function called Z Clean. Of course, not all newly added nodes are deleted. The nodes with the active geometry to be used are retained. Vanzhula has made the most common Houdini tools that he uses in his workflows quickly available to all users of his plug-in via corresponding Z buttons. These include the Subdivide SOP Node for refining geometry, the Poly Reduce SOP Node for reducing the number of polygons and the Delta Mush SOP Node for quasi-adaptive smoothing of geometry. The shelf contains separate Z nodes for all three functions.
But it is not only well thought-out Houdini nodes that can be called up directly in the Z Shelf. Important tools from ZBrush in addition to the Remesher have also been integrated into the narrow circle of selected functions. For users, this means in detail that the Move Brush and the Z Modeler Brush can be activated from Houdini and users can find themselves directly in ZBrush with the activated brush. The plug-in takes over the smooth exchange between the two packages in the background. As a rule, there are work steps that would be desirable but cannot be found in a predefined tool list. We are talking about user-specific functions that can be initiated via scripts. ZBrush offers the option of using ZScripts. From version 1.1 of Z for Houdini, the ZScripts can be integrated from Houdini in order to prepare the geometry based on the code contained in the script. To do this, open the settings window and insert the snippet in the Post-ExportZScript area. Click on Z Edit to execute the script.
Conclusion: Very promising
The work that Alexey Vanzhula has done is very promising. At least if both software packages are already licensed and the benefits of the plug-in have a direct positive effect on the underlying pipeline. On the cost side, the plug-in must first be factored in. The plug-in is available via Gumroad (www.gumroad.com) and is easy to find using the search function. Houdini versions from 10 to the latest version are supported. The supported operating systems include Windows and GNU/Linux. The developer charges 20 US dollars before tax for the use of the plug-in, which results in a price of 23.80 US dollars after adding German VAT.
SideFX offers Houdini as part of the Independent Developer Programme for 269 US dollars for one year. A two-year purchase costs 399 US dollars. Both licence models must be renewed after the specified period. Pixologic offers the latest version of ZBrush as a single licence for USD 895 before tax. The three cost centres should be known in case one of the two packages is missing and the budget needs to be recorded. In this case, studios still have to factor in the personnel costs and additional costs for workstations, etc. The bundle of all three packages is ideal if additional plug-ins come into play, for example to create a photogrammetry pipeline or to create a pipeline for the creation and animation of 3D characters that is to be designed flexibly. In Houdini, ZBrush models can be prepared for a crowd simulation in no time at all. Houdini enthusiasts would even question the plug-in altogether, as with in-depth knowledge of the software, the retopology process is also possible in Houdini in addition to attribute painting. Nevertheless, there are functions that are exclusive to ZBrush, and seasoned 3D character artists rely on ZBrush. If 3D character modelling artists want to get in touch with Houdini FX to quickly prepare characters for large animations and simulations, then the 23.80 US dollars are well spent.
Furthermore, it remains to be seen which well-considered functions will find a place in the Z Shelf. The plug-in appears to be relatively new, as the first demonstration video found its way online in mid-December 2018. The excitement remains and ultimately it is also important that only well-considered and self-tested functions end up in the Z Shelf instead of a blind implementation of all possible functions. Especially at a time when DCC software packages are bursting with complexity and the search for required functions and the customisation of packages to suit individual needs is taking up more and more time. If users would like to get a more detailed picture of the developer Alexey Vanzhula, we recommend taking a look at his Patreon page. He chose his name as his username. In addition to Z for Houdini, you can also find other little Houdini helpers for everyday modelling there
