Xgen After I Left the Xgen Tool I Cant Start Grooming Again
Stefano Giorgetti's 2013 character FX reel. Beneath, the Digital Domain graphic symbol developer provides x product-proven tips for using Maya'southward XGen instancing framework to create meliorate fur, hair and vegetation.
Procedural instancing enables artists to generate, animate and return vast amounts of geometry more efficiently. It is well suited to creating visually complex assets such as fur, hair or feathers, as well every bit large-scale environments like forests, grassy fields and rocky landscapes. Every bit computational ability increases, instancing is becoming an increasingly integral office of the surfacing and shading procedure in modern CG pipelines.
Adult at Walt Disney Blitheness Studios, and integrated into Maya 2016, XGen is a powerful instancing framework. It lets you distribute arbitrary geometry over a surface by means of maps, expressions and guides. It is essentially an interface to a complex render procedural and tin exist, in a way, considered a full shading tool.
The following tips are designed to make your workflow more flexible when using XGen in production, enabling you to adjust the changes that characteristic work requires. Although they are all tailored to Maya, they can be considered general guidelines when producing new work using any instancing framework. This isn't a beginner's guide, so nosotros'll be assuming that y'all already have some familiarity with basic XGen workflows.
The base model in the images below is 0a Blonde Girl, a free asset available via TurboSquid.
Make up one's mind early whether you desire to use guides to control instanced geometry, or adopt a fully procedural workflow. The sooner yous lock this decision, the better able you volition be to bargain with changes.
1. Plan your nugget start
Thinking about how are you going to structure your workflow is paramount to getting work washed on time. When yous create a new Clarification, XGen launches a wizard to guide yous through the key decisions. Although you tin switch later, the blazon of assets you are going to produce will make up one's mind the type of workflow you use.
In general, I like to utilize a full procedural workflow for instancing short, densely packed objects, like fur and scales, or environments. For long hair, it is best practice to commencement off with guides to describe each hair dodder, which provides more control over root-to-tip variations.
Mock up your asset using low-res geometry earlier you begin working with XGen. When creating long hair, simple tubes will give y'all a skilful idea of how the hairstyle will await before you create the instanced curves.
two. Block out your look
Before creating any XGen nodes, mock up your asset using simple, low-resolution geometry. Yous're basically sketching the layout that you are going to fill with instances or primitives. This will help you structure your piece of work.
Let's consider the common example of clumpy or curly hair. It is important that yous block the look with simple geometries such as tubes. (XGen actually offers a groom-from-tubes workflow.) These are like shooting fish in a barrel to model and will give a very practiced thought of what the hair style will expect like once it is translated into actual instanced curves.
Mock-ups are often used for the get-go round of feedback, enabling y'all to receive notes before yous have created a single instance. Establishing a proficient representation of the volumes of an nugget early will also help later on when running material simulations, and to ensure a clean, manageable result.
Dividing your blocking geometry into layers forces yous to focus on the individual characteristics of each i. Y'all will replicate the workflow in XGen later on, grouping sets of instancing Descriptions in to Collections.
3. Organise the blocking model in layers
Once yous have figured out the overall expect of your nugget, split the blocking geometry up into layers. XGen uses the same workflow, enabling – or even forcing – you to group sets of instancing Descriptions into Collections.
Working in sections forces y'all focus on each ane individually, and enables you to progress on unlike fronts in parallel. In addition, not having a monolithic look tin can exist a life-saver, particularly in big productions, since information technology avoids having to start again from scratch to suit unexpected changes.
Although guides can exist a powerful option for small, static set-ups, using maps to command instances keeps your nugget fully procedural, making it easier to accommodate changes later in production.
4. Go on everything you lot can procedural
XGen provides you lot with ii substantially different ways to control instances: guides and maps/expressions.
Guides are placeholders that ascertain the shape of an instance at a particular bespeak on a surface. The shapes of the other instances are generated by interpolating between the guides. In a static set up-up, this is a powerful, flexible approach, since you tin add or reshape guides at will. Notwithstanding, if not used carefully, guides tin can get out of control, making it difficult to manage the asset later.
I personally prefer to use maps or expressions to control instances, since they proceed the nugget fully procedural – and therefore flexible. When working in this way, refine the look iteratively: brainstorm with broad strokes defining the basic await, then use layers and masks to add details progressively.
A generic scalp geometry shrink-wrapped to a caput model. Placing your instances on the scalp geometry rather than the head itself protects your XGen fix-up from changes to the topology of the base of operations model.
5. Use scalp geometries
One of the major weakness of XGen is that is topology-dependent, pregnant that if the base mesh changes, you need to transfer your groom – the Collection of Descriptions – to the new geometry. Depending on the complexity of your set-upward, this tin can be time-consuming, or fifty-fifty impossible.
But in a production environment, where you are working in conjunction with other departments, things change often – and oftentimes drastically. An update to a model may alter the vertex order of the mesh, for example.
A skillful way to get effectually this is to use scalp geometries, which you own and manage. These are usually non-renderable, low-resolution models that wrap around the renderable mesh and deform forth with it. Placing your instances on this in-between surface rather than the renderable mesh helps you lot avoid surprises.
A Maya strength field driving XGen splines via nHair. In shots where it is not possible to employ XGen'due south own dynamic solver, structure your rig in such a way that blitheness and dynamics are kept divide.
6. Split dynamics and blitheness
If you are working on an nugget that will exist animated, defining the static look of the asset is only one-half the boxing. It is important to think about how your groom will behave when animated. There are 2 types of move involved here: animation and simulation. The onetime is the motion of the base mesh; the latter is the reaction of the instances to the animated mesh – and, eventually, to external forces.
Start, permit's call back about animation. The bones job is to become the instances post-obit the underlying mesh gracefully – and more importantly, without popping. When meshes deform, they alter the spatial relationship of instances betwixt frames, which tin can create artefacts. XGen provides different techniques to avert popping – Autodesk recommends using Patch References (PRefs) – which y'all will need to employ to create a successful sequence of rendered images.
Once you have the base of operations mesh animated and the instances post-obit information technology without artefacts, it's time for simulation. XGen has its own dynamic solver, which is great for basic simulations. It's simple, and oftentimes, it's but enough to get your shot through. Only when working on hero assets, y'all may need a more sophisticated solver, or even to pass the asset over to another department that handles that role of the piece of work.
In such cases, you want to keep blitheness and simulation separate, then 'plug in' the event of the simulation afterwards. These results usually come up in the grade of geometry caches, so your rig needs to be able to brand apply of them: for case, through Wire Deformers, or by ingesting animated guides that drive the hair clumps.
A basic render of an XGen set-up in V-Ray. XGen ships with readymade mental ray and RenderMan material and shading nodes, but you lot can apply its utility nodes to render your set-up with other renderers.
7. Use utility nodes to plug in other renderers
XGen is tightly integrated with mental ray and RenderMan, and ships with its own shading and cloth nodes for these renderers. These provide a comprehensive set of templates for common scenarios, enabling you lot to establish the expect and feel of a gear up-up quickly.
Just every bit with dynamics, the chances are that in a production surround, look development, lighting and rendering will each exist handled past a different squad member – and maybe, using unlike renderers.
In such cases, you can make use of XGen'due south utility nodes to map the UV surface in order to apply any material or ramp, or even an entire shading network, to your groom. This enables you to achieve a more complex look. There are a lot of nodes that you tin employ, just the one that volition exist most useful here is xgen_ptex_lookup.
A typical Ptex texture file of the type used by XGen. Ptex files are distortion-free, merely not human-readable, and so annal your maps in other formats as well, peculiarly if you will need to edit them in Photoshop.
8. Save texture maps in standard formats as well equally Ptex
The underlying map lookup in XGen is based on Ptex, a texture format developed at Disney. Ptex has plenty of advantages over approved UV mapping. The master 1 is that it is distortion-gratis, equally each of a polygon's faces are projected one by one, and mapped into a single texture file.
The disadvantage is that PTex textures are topology-dependent. Change fifty-fifty a single face of the mesh, and yous will probably need to proceed with a transfer. If you have many maps driving your rig, this tin be a pain.
In Maya, when you lot paint a map, you are actually using Maya's own 3D pigment tools on classic UV sets. When you press the Salve push button, Maya automatically converts the map into Ptex format. Make sure y'all relieve and archive the original, non-Ptex maps carefully. These tin plow into life-savers when y'all demand to transfer your groom.
Some other thing to consider is that Ptex maps are not human-readable, since the texture patches are arranged randomly, without any spatial reference to the actual geometry. If you are going to demand to edit your maps in an external application like Photoshop, having them archived in pre-Ptex format becomes fifty-fifty more important.
A set of copse instanced via XGen archives. You can export standard Maya geometry in a scene file as XGen annal geometry, enabling you to alter a base mesh and re-consign it to create variation beyond instances.
ix. Make good apply of archives
Geometry instancing in XGen is achieved via archives. These are files that shop the geometry for a single instance. You lot tin can and then identify the geometry over and over, in the same way you would XGen's ain primitives.
This is useful when you want to create, say, scales on a character or trees in a forest, since you just need to store the geometry in retentivity once, making information technology possible to create and manipulate extremely dense avails.
Equally with primitives, y'all tin use guides, maps or expressions to control variations between instances. Again, I similar to stay procedural where possible. Achieve a good overall look, then add detail progressively – for example, by modifying and re-exporting the case using XGen's Create MEL File choice.
Y'all may also want to breathing the geometry: for instance, to add together a wind cycle to a tree. XGen can role as a basic sequencer, offsetting the animations via expressions. Utilise the $frame variable and the sky is the limit.
A completed XGen hair system. When constructing an nugget for production, always exit scope to finesse farthermost poses and simulation errors on a per-shot ground – past brute strength, if necessary.
x. Build in animate space for final changes
When working with the surface of blithe assets, you are both modelling and rigging at the same fourth dimension. Every bit you build your static grapheme y'all need to anticipate the behaviour of the instances in a range of animated poses.
In reality, information technology is very rare that your rig stand up to the complete range of motions a character performs, meaning that you need to apply fixes on a per-shot ground. Information technology is paramount that you take a strategy for incorporating these fixes. You need to programme in a bit of 'breathing space' for terminal retouches.
This is the master reason I prefer procedural set-ups over not-procedural ones: at this stage, you lot are nearly forced to use not-procedural techniques to straighten out the unwanted outcomes, and you don't desire the fixes to accept knock-on effects. The best way of structuring the initial rig varies drastically from project to projection, but the need to make it open to changes is universal.
Tags: advice, archives, blocking out, character developer, grapheme FX, Digital Domain, dynamics, flexible, free, fur, hair, instancing, Maya, Maya 2016, organisation, procedural, production, real globe, rendering, scalp geometry, Stefano Georgetti, tips, Training, tutorial, vegetation, Walt Disney Animation Studios, XGen
Source: http://www.cgchannel.com/2015/06/10-tips-for-using-mayas-xgen-in-production/
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