Wednesday Battle: LUA vs FPI

Performance Day

Thursday I will be out of the office getting my eyeballs replaced, but today was all about performance profiling and answering emails, and then some more performance profiling.

The good news is that I have gone from 21fps to 45fps. The bad news is that I had to switch off all shadows to do it ;)  Better news is that I discovered that some file map communication code written to obtain Windows mouse coordinates from the parent IDE application was a serious drain, and upon removing it (only needed for actual TAB page views) rescued some substantial performance back from (or should that be for) the engine.

I have also extended the division of metrics within the main engine so I can see at a glance more fine grain detail of what the engine cycle is doing.

As you can see, apart from Misc2 (which I am still investigating but suspected to be a rogue value), the main energy draws are from the rendering step which is the GPU stall while it produces the visual you see above, and a little bit of terrain and AI processing. When I include the shadow rendering, all other performance considerations shrink and it seems the performance is entirely dictated by the amount of 'rendering and shadow rendering' being done by the engine.

In a way this is good, as I can focus plenty of effort on a single module for instant speed-up. I also have some great tools to assist me, and I know for a fact I can create multiple techniques within the shader to suit different system specifications (for LOW, MEDIUM and HIGH).  It's pretty good fun performance profiling as you have nothing to lose and everything to gain, and can be quite a buzz when you gain a few FPS.  Much more to come!

The Big Debate: FPI vs LUA

Ever since the idea was proposed, the topic of which scripting language is better for Reloaded has been pretty hot of late and I have been asked to step in and clarify the situation as to where we are.

I wrote the FPI (FPSC Instructions) language to quickly allow for simple conditions and actions within the game world. It was never meant to be a language as such, and a million light years away from something like DBP. It was ideal for quick one liners, such as turn on a light when you enter a zone, but became almost laughable when you asked it to coordinate the mental abstractions of an ally character following you around a combat scene. I would even cringe at having to apply a state value half way through the script, so that the subsequent conditions where skipped, only to set he state value to the intended value at the end of the script. If you read that in pseudo-code, you'd severely admonish the student responsible:

IF A=1 THEN A=3
IF A=2 THEN DO THING COOL
IF A=3 THEN A=2

The FPI language scores marks for being one of the smallest language on earth, it's syntax almost entirely comprising of a colon and semi-colon. It is perhaps this simple format that has earned it such popularity, and when you start to study the built-in scripts, you're guaranteed to learn the logic within a few minutes.

The basic problem with FPI is that the underlying 'interpreter engine' which processes all the commands is written in DBP, and so each command is actually a trigger point for a multitude of other commands to fire before returning to the main thread. Multiply this with the many commands found in the script, and then by the hundreds of entities that are firing off said scripts and you have a substantial drain on overall performance. Indeed, one of the complaints levied against the classic version of FPSC was that too many scripts in a level would start to depreciate frame rate and force the the creator to clear their level of heavy scripts, divide up their levels or worse, scrap their ambitions for more attainable goals.

When we arrived at the decision to scrap the segment system and re-imagine a new way to construct large buildings and structures, it gave us the confidence to ask similar questions about other parts of the system. As fond as we are about FPI, we also know it is the silent assassin of many large and ambitious levels, and if we are to aim high we must look critically at each part of the whole.

Understand that we have not decided unilaterally to drop FPI and instate LUA. We still have to do some prototyping and profiling to see whether the integration of LUA is viable and improves performance of the engine. There is also the possibility of moving FPI into the core engine, executing the instructions outside of DBP. Therefore, you can rest uneasy in the knowledge a decision has not yet been made, and every effort will be made to work out which solution is best for Reloaded. To that end, you are welcome to continue this discussion, and hopefully arrive at a consensus as to ease of use and suitability.

A Question Of Ease

FPI is easier than LUA. LUA is much nicer than FPI. FPI is simpler than LUA. LUA is easier to read then FPI. The mystery is that all these sentences are correct. Based on who you are, you will find a sentence you can agree with. I think each has their charms. Unfortunately I have been in the situation of supporting two parallel paths of near identical functionality before and I must confess that supporting both can be agonizing and demoralizing. It was this past experience that lead me to conclude there should be only one. It was this decision that fired up the debate we are all enjoying.

I was fortunate enough to have spent a few years teaching at Masters degree level, and I learned a few things about 'ease of use' or more accurately 'ease of understanding'. Just as secret knowledge becomes commonplace once explained, so to does a script or language. If you learned FPI, you can learn LUA. If you know LUA, you can learn FPI. The underlying lessons are identical! If THIS happens, do THAT. I'm afraid that's what programming boils down to. If THIS, then do THAT.

From a personal point of view, and this is from a coder who's regrettably forgotten more languages that he presently knows, the syntax of LUA is very reminiscent of BASIC, which remains my all time favorite language. The idea of IF X THEN Y ENDIF really makes sense to me, and is the principal building block of any large electronic edifice. My prediction is that there will be more scripters for Reloaded than we ever had with FPI, not least because the scripts we will provide will become readable!

A final note addressing Reloaded ease of use. We are designing the software so that scripting by no means a requirement of the creative process. In fact, I expect only around 5% of users should ever need to break out into the world of scripting. The remaining 95% will find the combination of entity properties, sliders for in-game adjustment and level configuration more than sufficient to create a unique experience for your users. The scripting is there for those brave souls brazen enough to think they can create better scripts than TGC :) Rest assured that we will provide a wide variety of LUA scripts, assigned by default to relevant assets, dealing with all the game functionalties you require from opening a locked door, to commanding a battalion of soldiers to follow you into hell. You only have to look at our history of products to know that 'ease of use' is one of the goals we constantly strive for, and we understand that many of you have no desire to program, and why you use FPSC in the first place.

What's Next

You will want to know what happens now. What is the decision! For this I will need to create one or two prototypes, principally to test how the integration into the main Reloaded engine will be, and also to check whether the performance benefits are worth the transition. I also want to study the existing FPI language (which has doubled in size since the modders took over) and understand the scope of maintaining and/or moving it to a more internal engine that can process at higher speeds. 

Aside from the professional reasons, I also want time to play with the LUA syntax and get a feel for how it might work inside the Reloaded universe, and whether it is a good fit. LUA is not the only scripting language out there, and my researches might turn up something newer and more shiny! I also promise to try and resist the urge to create a new language for the occasion :)

Signing Off

Hopefully I have brought everything up to date, and hopefully I can bring you more performance improvement news Thursday evening, when I explore the deeper GPU realms and return with some worthy finds.

A Bit Of Fun

Rick decided to film an impromptu video as we concluded our meeting on Tuesday, and then put it on YouTube (bless him). Just in case you missed it, I have hosted it here so you don't miss out on any of my mindless waffle.

Once Reloaded is in a state where I can show my face in public, I am pretty sure there will be plenty more videos for you (and me) to cringe over.