"Soft Engine", Breast Physics, and Gravure Studio

Picture this: It's 2015, and Dead or Alive 5: Last Round has just been announced for PC. While PC ports of Japanese games are commonplace now, this was a fairly rare occurrence at the time, and in the case of Dead or Alive, this was a first for the franchise.

While PC ports are always anticipated releases, as the PC platform is the most versatile and powerful, in the case of DOA, this was going to open the floodgates for a burgeoning community of modders that've otherwise struggled against all odds to make even the most rudimentary mods for consoles, which is no easy feat.

In fact, Koei Tecmo created a landmark ruling on modders for DOA on Xbox, being the first civil suit successfully lobbied against erotic mods. One might be fooled into thinking this would create a chilling effect for the DOA5 PC modding community. In fact, Koei Tecmo would release a statement ahead of the release for Last Round for PC warning against "immoral" mods. While the wording is humorous, the message was clear: they viewed erotic mods as damaging to the DOA intellectual property, and they would take action against those who make them.

But the current was too strong, and Koei Tecmo doesn't have a monolithic suite of legal retainers to fight the tide that would be unleashed from a PC port of Dead or Alive, and the result is self evident. While Koei Tecmo has nonetheless taken action against clearcut cases since then, like this person selling DVD's of modded videos of DOAXVV, the rest of the modding community has remained unmolested by legal notices and civil suits. Modding tools and thousands of mods have been made for DOA5 and DOAXVV, and beyond the confines of the games themselves, models of the DOA women have proliferated in SFM, Blender renders and animations to in a rush that'd otherwise been dammed by the closed console platforms and their inscrutable devkit encryption. I'm proud to view myself as a pre-eminent figure in Dead or Alive modding, as funny as that is to say out loud.

You might be wondering...

Why this trip down memory lane? Admittedly the stuff I just talked about was mostly for my own amusement, but I promise I'm getting somewhere. While the news of a PC port of DOA5: Last Round was tremendous news for those with a possibly immoral interest in the Dead or Alive franchise, tragic news would strike before the games release: the port would be based off the Arcade version of Dead or Alive 5.

This choice as a developer is obvious: arcade machines are more similar to PC's than consoles are, so it would be easier to retrofit it for a PC release. However, the arcade version is out of date, and lacks features from the latest and greatest PS4/XB1 release. Some costumes and stages are missing, but most tragic of all for the purposes of DOA modders was one thing: no "Soft Engine"

...but what even is the "Soft Engine"? Despite how little press was given to this feature, gamers of culture rapidly circulated a video touting the Last Round re-releases' more advanced breast physics simulation that's admittedly hard to track down now. I've only managed to find a reupload of the official video on Dailymotion.

You can even see the soft engine logo in the video that would later be refurbished for DOAX3's "Soft Engine 2.0".

Naturally, people were upset. Just the optics of a substandard, lazy PC port had already become a touchy subject, but also substantively, lacking these seemingly more advanced breast physics seemed like a major blow for our purposes, and something as substantial as an "engine" would be very difficult to reproduce through modding... right? After all, without source code or a modding SDK, doing just about anything requires a fair amount of reverse engineering, and it's not like a physics engine is something that could be realistically produced through such means.

But now the dust has settled. It's been 8 years. Why don't we try and figure out exactly what Soft Engine "does" with more specificity to identify what we've lost. I encourage you to watch the video I've already hyperlinked, but just in case you didn't I'll link it again.

https://www.dailymotion.com/video/x3rz78t

Here we see a comparison of the PS3 version of Last Round with the PS4 version, which is powered by the new "Soft Engine". The first most obvious difference is in the very first clip, the Helena entrance scene. The breasts are almost entirely rigid in the PS3 version, while in the PS4 version her breasts are doing what you would expect them to do: bouncing.

This clip immediately drew my attention simply because now, with the power of hindsight, I knew the reason why this was happening, as I have a lot of history with this that I documented in a now pruned video. In Dead or Alive 5, cutscenes, movies, win/loss poses, all by default run at 30 frames per second. This is presumably to give it a filmic cinematic appearance, whereas the normal game runs at 60 frames per second, like when you're actually fighting.

The problem with this is that physics logic is tied to framerate, and as a result of which, cutting the framerate in half dramatically affects how the breast physics function. A very basic explanation of this is that the physics calculations compare the coordinates of the breast bones from one frame to the next, and determine how they should react by calculating the difference and applying a physics configuration to them (bones are the means by which a model is organized into moving parts).

I haven't looked at the code, obviously nobody but people who work with precompiled source code have, but what I suspect is happening is that the physics engine is configured for 60 fps, and when determining the physics coefficient, it's reading an identical frame half of the time it compares one frame to the previous, and as a result of which no momentum is being applied to the breasts, and as a result of which it's creating an unnatural stiffness in the breast physics.

While I can only proffer educated guesses as to why it's happening, I know for a fact that changing the cutscenes to run at 60fps and interpolating the animation frames fixed the problem.

So, in a way, that kind of makes the marketing for this "Soft Engine" seem a bit deceptive, no? At least in terms of the intensity of the bounce, what's being shown in the video is nothing more than a glorified bugfix, and certainly not something as dramatic as an entirely new physics engine powering the DOA5 breasts. It's worth noting that not a single piece of 60fps gameplay footage is shown in the trailer, even with a wealth of great examples of animations that would demonstrate breast physics adequately, like Tina or Honoka's idle animation where they bounce up and down. The simple reason for this is that in the actual main game, the breasts largely work as intended. You can boot up vanilla DOA5 for PC right now and watch breasts bounce in a manner no more sophisticated than what you see in that Helena clip. Here's just a random example from steamcommunity posts demonstrating this. 

So in that sense, I've already established half of Soft Engine years ago into the PC port of Dead or Alive 5 with the introduction of 60fps, right? Well, not quite. The trailer also demonstrates another important feature... gravity.

It's not as obvious as bouncing, but you can see here that in the left picture, the breasts are being pulled in the direction of gravity in a way the breasts on the right aren't. It might shock you to learn that there's little to no gravity being applied to breasts in Last Round PC or X360/PS3, and unlike the bouncing/momentum problem, this is not fixed by adjusting the framerate or animation interpolation frames.

So at this point you might think that a true casualty of the PC port has been discovered, surely this is a real, actual feature of Soft Engine that can't be easily salvaged... right? Indeed, this is what I thought for 8 years. That is, until 2 talented Japanese modders joined my Discord and answered my request to sift through the game's raw memory addresses in Cheat Engine to find a mesh toggle flag. However their curiosity was not limited to my request, and ever since they've been making new discoveries.

c d b d and ayanelove have been tinkering in the game's code for a while now, and among other things, have discovered all or most the memory addresses that pertain to breast physics. Ayanelove in particular has uploaded a multitude of clips on his twitter showcasing just how dramatically he can alter the physics to allow for deformation far more aggressive than what has been demonstrated in any iteration of DOA.

It might surprise you to learn that the values for gravitational pull exist already in the games code, and they had simply been switched off.

Off and On respectively

And with that, the final hurdle of the fabled "Soft Engine" is solved. Nothing stands between Gravure Studio and bouncy perfection any longer. I look forward to implementing these changes into the next version of Gravure Studio... and perhaps a fun preview video at some point along the way?

Thanks for reading.