An Introduction to Procedures

As there is a huge amount to cover I'm going to spread it out over multiple posts.  The first few will describe the technology (engine) and after that I'll cover the tooling (editor).  This will by no means cover all the technical detail, but it should give you a good idea of how it works and what (I hope) it will be able to do.

Authoring

Currently the engine allows building of procedural models; objects formed of triangles (and lines) and rendered in a 3D viewport.  These are expressed as 'procedures'; collections of modelling and calculation operations that feed into each other forming a network or graph.  The 'inputs' to this are various constant values within the graph and the output is a 'value' corresponding to the generated geometry.

A simple procedure and the resulting model

Each node is some form of fundamental operator (like add or subtract) implemented in code, or it can be another procedure, itself made from operators and procedures.  The term 'operator' will be used to mean either in the context of a procedures content as once placed down they can be treated in exactly the same way.

A multiplication operator feeding into a luminance procedure

Each operator generally has one or more inputs and one or more outputs, which can be connected up to other operators.  An input can only be connected to one output but an output can connect to multiple inputs.  There are several fundamental data types available for information to be passed between operators.  So far we have: Integer, Float, Bool, Colour, Vector, Matrix, String, Frame, and Model Segment.  These last two are explained more below.  Unconnected inputs are considered constants and the value can be explicitly specified.

Operator inputs of various data types

When creating a procedure, you get to define it's inputs and outputs, and their names and types, these then become available for connecting-to wherever an instance of the procedure is placed down.

Procedures represent blocks of functionality and can easily be used to encapsulate and re-use groups of operators.  For example you might build a colour blend procedure out of mathematical operators if a dedicated operator wasn't available or didn't meet your needs.

Bespoke colour blending procedure

The new blend procedure in use

Operators

There is a small library of built-in operators implemented already to build procedures from, these are roughly divided into:

• Mathematical operations - all the usual maths functions.
• Comparisons and conditional switching - test and flow control.
• Conversion - e.g. changing type or break-out/re-combine (for multi-element types).
• Constants - operator inputs are editable constants, but constant operators are useful for sharing values.
• Modelling - create and manipulate primitives (cube, cylinder, paint, distort, etc).
• Space defining - subdividing and specifying spaces to be used for containing objects (Frames).

Some of the operators available so far

There are hundreds more of these I need to support (something for a future post), but this is plenty for me to test and prove out the principals.  In fact this current limitation means I have to be inventive and really means I push the capabilities of the procedure system to see what I can achieve.

Modelling

Currently there are only two triangle primitives (Cube and Cylinder) and two line primitives (Line and Grid).  The only reason I haven't written more yet is that I have managed to achieve a surprising amount with just these.  All the screenshots you can see so-far are mostly built with the cube operator and an occasional cylinder.  As we will see though they do provide a fair bit of control over how each can actually be used.

Once I got to the point where the geometry synthesis was basically working and I started building shapes I found that a large part of building up objects is actually splitting up the space it is going to occupy into smaller spaces.  This happens at many depths and in many different ways.  There are parallels here to laying out elements on a page or in a user interface, so many concepts like centring, distribution, and offsetting apply equally to 3D space. To facilitate this in Apparance I found a data type to describe an oriented cuboid in space was ideal for this.  These I call 'frames' and operations on them form a large part of the object construction process.

Space partitioning operators in use (highlighted yellow)

Starting with a frame describing the location, orientation, and dimensions of the object being created, you break it down into sub-frames until you reach a point where a single primitive fits exactly, at which point you feed the frame into it generating the geometry needed there.  This aspect of modelling needs a post to its self really :)

Geometry generated by a primitive operator is passed around the graph using a 'Model Segment' data type.  This rather esoteric type is just a way of remembering where in the modelling buffers the vertex and triangle information for that primitive has been put.  A 'combine' operator is available to merge two segments of geometry together so they can be treated as one.  All modelling should result in a single Model Segment output at the top level and it is the geometry enclosed within it that will be displayed.

Part of the appeal (to me at least) of procedural generation is parameterisation.  Anything we build this way can have any aspect of its form exposed as a tweakable parameter.  This may just be the desired size of the object, it might be the thickness of the frame on window, the colour of a building's roof tiles, or the probability of a wonky brick in a wall.  In order for a given parameter to affect the modelling process its value will usually need to be massaged into some other form by using mathematical, conditional, and logic operators.

Synthesis

The process of turning procedures into models that can be rendered it called 'synthesis'.  Starting with a root procedure to be viewed in a 3D scene the synthesis engine starts by instantiating it in memory with any input values needed and requests the geometry via the appropriate output.  This triggers instantiation of all the operators within and their interconnections.  Following the 'flow' of the data connections back from the required output and digging down into procedure within procedure all the functionality needed to produce it is executed.  Requests for output values from leaf operators, ones with actual code behind them causes that code to be executed.  Procedures and operators also call upon their inputs which then cause the evaluation to elevate back up to the level above and follow the connections already in place when the containing procedure was evaluated.

Evaluation tree for the table example

Because procedures are instantiated as they are needed, it can support recursion, i.e. a procedure can include instances of itself.  As long as there are 'exit conditions' defined to limit the recursion depth this turns out to be a really useful way to build a lot of structures.  I discovered early on that this can be used to implement arrays of objects by progressively subdividing until the required object size was reached.  I thought I would need array support explicitly but so far recursion has served well in its absence.

A recursive procedure called "Recursive" that includes itself.

Output of the recursion example

To help with scalability and performance, multiple synthesis runs can be performed in parallel on several separate synthesiser instances.

Four synthesisers running in parallel, busy building geometry

Each has its own pre-allocated chunk of memory as working buffer, used in a non-freeing manner and only reset at the end of each run.  This makes allocation of parameters, values, operator state, and any intermediate data extremely fast and all values effectively immutable, simplifying the operator graph evaluation logic.

A breakdown of how memory was allocated during synthesis

Next

Quite a lot to absorb I'm sure.  I'm happy to answer any questions.  Next time I'll talk about the renderer, some of the less glamorous code supporting everything, and how the project is set up.

What is project "Apparance"?

Videogames

I have been making videogames for over twenty years, and the process always seems to go something like this:

1. Design game
2. Create assets
3. Write code
4. Test game
5. Repeat above in various combinations until done (ship or bust)

These steps are quite separate, mostly performed by different people (or groups of people), and the bigger the game the more of all this you need.

Some time ago I came to the conclusion that above a certain project size this model isn't very efficient for a variety of reasons. Firstly, because assets need to be worked on by multiple people, the friction associated with moving them around (conversion, source control, management, communication, builds, deployment, and loading) can mean lots of additional effort and add up to long and frustrating iteration times.  Secondly, as projects have become more ambitious, with larger scopes and game-play areas where the work involved in creating them increases exponentially (with area/volume), the cost also ramps up this way because the work a team puts in can only, at best, grow linearly with size.  In addition to this, a natural consequence of growing teams is the need for increasing communication, management, and support.  All of these pressures usually mean compromises being made to the game's detail, richness, variety, polish, quality, or seemingly low priority support work is neglected, in order to get it to fit within the budget.

Pondering this problem for several years I have formed a vision of how I think we can improve this construction and authoring process, and what the technology and tools it requires would look like.  I'm fed up with conventional approaches, the waste, the sluggish pace, the repetition, the tighter squeeze on the more fuzzy aspects of creativity like experimentation, play, fun, emergence, and instinct. I want to try working a different way, using novel and interesting techniques, powerful technology and tools, to empower smaller teams to create bigger things.  I believe we can do better, and whilst it won't be everyone's cup of tea, it's something I believe passionately in.

"I'm fed up with conventional approaches, the waste, the sluggish pace, the repetition, the tighter squeeze on the more fuzzy aspects of creativity like experimentation, play, fun, emergence, and instinct."

I've been working on this project in my spare time for around five years, with the original concept rolling around my brain for about five years before that.  As I described in my previous post I am now in the fortunate position to be able to invest all my time in this project.  So, what exactly is it I am proposing?

Vision

I want to enable rapid creation of rich and varied worlds through fully dynamic procedural generation.  I want to encourage play and exploration through fully interactive live editing of content and behaviours.  I want to make games in creative and exciting ways:

• Rich worlds full of the variety that parameterisation and procedural techniques can enable.
• Vast structures with intricate detail from highly scalable dynamic modelling.
• Endless continuous worlds with no loading and no transitions required.
• Don't repeat to save time, every instance can be unique in design and appearance.
• Instant feedback and fast iteration from rapid and responsive tools.
• The play and exploration that real-time control systems with live editing allows.
• Freedom from bulk assets and offline asset pipelines by going fully run-time procedural.
• Increasing the efficiency of creating content through asset modularity and easy reuse.
• Making extensive use of visual editing paradigms (data-flow, node-graph).
• Removing hard coded content, everything data driven.
• Small footprint applications yet with all the richness of today's larger titles.

There is nothing out there that does all this, the technology just don't exist. I see this project as an adventure where we are specialising in procedural generation and real-time interactive experiences that can be applied to a variety of applications; especially games, education, and interactive visualisations. If we aspire to travel to new lands but the vehicles to do so do not exist, we must first build them.

"If we aspire to travel to new lands but the vehicles to do so do not exist, we must first build them."

What it is

This is an authoring environment in which to create your worlds, populate them, and bring them to life. The real-time synthesis engine uses procedural definitions, their input parameters, and the surrounding environment to dynamically fill out the world in more and more detail as you explore.

Apparance Editor - Procedure graph for roof section of an old house

The editor provides authoring and testing of the world through a visual flow based editing model (nodes and wires) to create the procedure definitions describing the geometry, texturing, effects, physics, behaviour, logic, and much, much more.

A standalone player application provides a non-editable view of world, for test, play, and release.
The underlying engine contains the technology driving both editor and game, using highly concurrent operation, with dynamic detail management, largely stateless data-flow control and AI systems, and all with live editing/monitoring during authoring and play.

What it is not

It is not a silver bullet and won't solve everyone's problems; Some games won't fit the development model and technology being created here.  It may be that a game relies heavily on areas that are a particular weakness for this technology. Some games are based on very tightly controlled and designed environments and behaviours. But I believe that working toward its strengths and away from its weaknesses is no different to any existing games development, more so historically as hardware and software capabilities have applied their own unique constraints on possibility.

I don't see it as a plugin for other engines; using a lot of unique techniques to achieve its aims means it may not work well in more conventional engine scene graphs and rendering.  The lack of scalability in many existing systems can cause problems too as non-scaling systems 'crowd-out' the scalable ones as a project grows.  This is a disruptive technology, and relies a lot on the interaction between the various novel techniques at play.

It is not finished yet.  This is a project that I've been working on in my spare time, and whilst showing great promise already, there is still a lot to do to.  I see many stages to its development and I will be building demonstrations and even games to show-case it at various points in the future.

Direction

This is an ongoing project and I want to involve people as it develops.  Through blogging and sharing the results of my work I hope to involve like-minded and creative people to help shape the tech and tools into something that many developers could benefit from.  I am working towards releasing versions of the tools for you all to play with to see what we can create together.  If you are interested in these ideas and the prospect of trying something different please get in touch via email, via my Twitter feed, or just follow progress here on my blog.

The Name

Logo design idea - featuring one of the first models built with the system.

Apparance (or often Apparence) refers to the outward manifestation of a person or thing, the act of being visible, what others see, the process of creating this external impression. The original inspiration for this comes from "Against A Dark Background" by Iain M Banks; The Solipsists don't subscribe to the concept of the individual with no use of the word 'me', referring to, and in a way justifying, the existence of other members of their group as 'apparences'.

Next

Next time I will bring you a full project status report, showing the current state of play and what I'm working towards at the moment.  It should be a very visual post as there is lots to see.

New Beginnings

Tragedy

Nearly three months ago now, everyone at Lionhead was called into a company meeting at short notice to be told that Fable Legends was probably going to be shut down and the studio along with it.  Roll forward to the end of April and the axe finally fell leaving over a hundred developers, a four year project, a smaller side project, and a 20 year old studio, gone.  I don't expect we will ever know the true logic applied by Microsoft to drive this decision, and I'm sure many will speculate on this for a long time. However, due to both the huge amount of talent among the staff and a great rally of  support from the industry I am please to say most (if not all) of my displaced colleagues have found new roles, pursuits, challenges, and adventures to move on to.

The last Lionhead team photo

Opportunity

In a way I have a little difficulty coming to terms with, such tragedy has led to the opening up of a significant opportunity for me.  It has become an enabler, in the form of both a financial safety net and huge prod, to do something new.  I had been at Lionhead for over eleven years and seen a lot of change, but I was still happy there building tools and technology to support the team in making the fantastic Fable visions come to life.  I have mused about quitting to develop my personal projects before, but either the numbers didn't stack up, or the time wasn't good, or I was enjoying work.  This however presents an unavoidable boot up the backside to give it a go... and that is what I am doing.

Cogitation

This infrequently updated (and lesser read) blog that you are reading now has been my attempt to slowly document development of a spare-time project over the last five years.  It is based around a collection of ideas I've been pondering since around 2001, gradually crystallising all the different elements of what is needed to produce some exciting procedural technology that I feel should exist.  I will go into the project details in my next post, trying to finally bring together and explain all the many aspects of my vision, for now you can refer to some of my previous posts for an overview.

Introspection

During the redundancy process we all felt a bit in limbo, not really sure what was happening, or what we should be doing.  With no work to do, we were largely at a bit of a loss.  Some dusted off their CVs and job hunted, some taught themselves new things, some tinkered, some played games, some just didn't come into work.  I had some loose ends to tie up but after a while started spending more time at home on some long overdue bathroom renovation.  This served as a productive use of my time, keeping me busy, and also providing some much needed thinking space, to mull over the possibilities and directions to go.

Preparation

Redundancy included various consultation sessions and training opportunities, which I decided to give a try.  These turned out to be very useful, providing me with a good overview of self-employment, and advice on using social media and the web to drive business.  Conversations with a few friends and family members about my thoughts, concerns, and plans helped too.  Going forward I decided (at least to start with) that a self-employed, one-man-band operation would serve me best.  I have a nice office set up in our spare room (a pleasant environment with desk, chair, PC, light, supplies, etc).  Office hours have been decided (9 to 4:30, flexible).  House rules have been negotiated ('Daddy will still be working when you get home from school'). I am good to go.

Action

This weekend marks the end of my first week of my new job; working for myself, developing my project full-time.  It was always going to be a strange experience, having been an employee all my working life, but I can see myself getting used to it fairly quickly.  I like the fact that I am working on something I am truly passionate about, something that can only come from being the source of the ideas. It is weird that my spare-time project has replaced my work project and that my spare-time will need to become something else.  I will have to be careful to dedicate spare time to more varied interests as I now more than ever need to keep myself mentally balanced.

Prediction

It's a hugely exciting prospect to develop my project properly, investing the time it deserves, and giving it my full focus.  I am pretty certain that it will result in some impressive and useful results and I can't wait to share with you fruits of my labour and the process by which I achieve them.  Please join me as I embark on this adventure. I will take you through some of the business, and personal sides of it but mostly this will be a technical blog (and there is a lot of technical involved).  Exciting things are on the horizon; watch this space...