Dissecting Sega Saturn Doom

Great read Mattfriel. I wasn't even aware of a Sega Saturn Doom port. The only console ports from back in the day I knew were the PS1 3DO SNES Jaguar and 32X ports. And IMO PS1 got the best console Doom port for the time, wasn't really until Doom 3 BFG edition when consoles finally got a 100% accurate port of the PC version.

My goodness, the frame rate on Saturn Doom is just miserable even when relatively little is going on.

The saturn version of doom is the very first doom i ever played, and it's really what got me interested in doom as a whole. Still have my saturn and copy of doom for it, I enjoyed it and still do. The framerate can get pretty bad, and having played tons of other ports of doom, i really have come to dislike the music. When i had nothing to compare it to it was alright but i think doing something like 3do version did with the soundtrack would have really been awesome

19 hours ago, Mattfrie1 said:

- All of the map files for the Saturn port are the same exact file size as the map files for the PSX port, and examining the files in a hex editor reveals absolutely NO difference between the files as well. Since the files are an exact match, I wonder if all the information about colored lighting and sound reverberation are still included in the Saturn files...

Almost certainly. Both fields are in the mapsector_t struct, though I have yet to figure out the meaning of the SPU control field's values in PSX. The lighting field is a byte index (0-255) into the LIGHTS lump.

If you've isolated the assembly for P_LoadSectors, I'd be happy to post the MIPS ASM from the PSX version for a direct comparison.

1 hour ago, imradlol said:

When i had nothing to compare it to it was alright but i think doing something like 3do version did with the soundtrack would have really been awesome

There's an ISO hack of the Saturn DOOM that replaces all the songs with the 3DO port songs. I have yet to try it, but you can search for it on Google.

1 hour ago, Quasar said:

If you've isolated the assembly for P_LoadSectors, I'd be happy to post the MIPS ASM from the PSX version for a direct comparison.

I'll just post a screen grab of what I'm seeing in the hex editor, I'm pretty sure this is what you're looking for.

https://imgur.com/68uuEbx

Aside from that, I did another comparison of the source WAD files (PSXDOOM.WAD and JIMSDOOM.WAD) between the two ports in Slade. Both of these files are ALMOST identical, but there are several entries which appear to be corrupted in JIMSDOOM.WAD. BSPIC2C8 (an arachnotron walking sprite) is only 5.52 kb in JIMSDOOM, whereas it's 7.02 kb in PSXDOOM. SKELG2 (A revenant punching sprite) also doesn't display in JIMSDOOM, but is the same file size as PSXDOOM. Both of these sprites still display correctly in game however.

Just for the hell of it, I put both PSXDOOM.WAD and JIMSDOOM.WAD through the hex editor, even though I already know that JIMSDOOM is a lot bigger in file size than PSXDOOM. I've attached screen grabs of the end of both WADS in hex below.

https://imgur.com/pYzAzZS

https://imgur.com/7a1LWHp

On 1/14/2018 at 8:17 PM, Mattfrie1 said:

- I also feel the need to point out that since the Saturn uses an entirely different sound engine from the PSX version, there was no possible way that this port could have supported sound reverberation effects, especially since the reverberation effect was a feature of the PSX's sound processor. As far as I know, the Sega Saturn's sound processor had no equivalent feature.

First at all, thanks for you research and post.

Only one note. SS have this effect by hardware. Even more effects. SS have a DSP in sound chip. The problem here is that not than easy use like PSX. In SS is necessary more work to make the same, and in this years, extra SoundBox for that. In the end of life all sound stuff improve it, and not necesary Soundbox, like the 3D and lighting  in SS.

Regards,

I love the Saturn and I love Doom, but that port is just god awful. It's so damn janky that I can't even play it more than 15 minutes before my head starts to hurt.

I've gotten a new capture card setup recently, so I figured I'd revisit my old friend Saturn Doom.

As stated on it's Doomwiki page, PSX Doom has a bug where lost souls outside of level boundaries can cause a level to get corrupted. I figured that since many aspects of PSX Doom are mirrored in the Saturn port, the bug would be possible to duplicate in this version as well.

The video features two instances of the bug happening. Perhaps the most interesting event occurs at the 3 1/2 minute mark where I look on the other side of a transparent gate texture. The game draws a bunch of random colored pixels on the other side of transparent textures. Although it is distorted, you can see some of the blocks of color flashing to different colors in a fixed pattern. The way they are laid out remind me of a color palette, but I have no way of proving exactly what it is at this time. The same effect can be spotted again for a split second right before the 9 1/2 minute mark on the other side of the cages where the pain elementals spawn in the final area. Not sure if this same thing happens when the glitch is done in PSX Doom, but I couldn't spot it from the one YouTube video that exists of the glitch.

I actually manage to exit the level on the first attempt shown in the video, but the game freezes on the other attempt. No error message or black screen like PSX Doom however (even though all the error messages remain in the Saturn version's code), just the screen freezing with the game's music still playing unaffected in the background.

On 6/25/2019 at 8:18 PM, Mattfrie1 said:

The game draws a bunch of random colored pixels on the other side of transparent textures. Although it is distorted, you can see some of the blocks of color flashing to different colors in a fixed pattern. The way they are laid out remind me of a color palette, but I have no way of proving exactly what it is at this time. The same effect can be spotted again for a split second right before the 9 1/2 minute mark on the other side of the cages where the pain elementals spawn in the final area. Not sure if this same thing happens when the glitch is done in PSX Doom.

Hey, I'm sure that rainbow thing means the back side of the midgate lacks the texture (on its other side only). I'm familiar with that thing, as happens in the psx as well (we did map conversions for [GEC] project where you often could see reason of this in your custom levels).

Thanks for the heads up @mr-around. Not surprising to hear the same thing happens in PSX Doom.

I've been looking around some more in a Saturn emulator to try to figure out some more clues as to how the game operates:

- Level rendering appears to be handled in the same way as the PSX version as described on the last page, but instead of using quads the system is using distorted sprites to draw each individual column. This was a very common practice that Saturn programmers used in many 3D games on the system, and rendering of these sprites is handled by the Saturn's VDP1 graphics chip. Keep in mind however Saturn Doom emulation is still very buggy, so I'm assuming this is actually how the system operates and not a bug of the emulator.

- There's a few Action Replay / Gameshark codes for the Saturn port floating around the web. Most of the codes are for rather simplisitic things such as maxing out your ammo or giving certain inventory items, but one is for changing the firing speed of your weapons which I found rather interesting. I messed around with the values on my actual console and found that setting the bytes to all zeroes cause the weapons to not load in at all, leaving you running around the level helpless. Setting to any other value besides 0001 causes weapon behavior to become very glitchy and hang up on random firing frames.

Using the Saturn emulator's memory editor for reference and the Action Replay I've been able to edit a few things here and there in memory without making the game crash. I'm trying to cross-reference with the PSX port as well (PSXDOOM.EXE from the game disc) to see any noticeable differences between the two.

- Changing the two bytes between LIGHTS and PLAYPAL change the overall intensity of the lights in a level. The higher the value entered, the darker the lighting becomes overall.

- In regards to this, the Saturn version looks like it could be using it's own unique PLAYPAL file instead of the one supplied in the main resource WAD. There is an extra file on the Saturn Doom disc called PLAYPAL.PAL which is referenced after LIGHTS in memory. Keep in mind that PSX Doom's PLAYPAL is still on the disc in the overall resource WAD (JIMSDOOM.WAD).

I've managed to somewhat fix the issue this port has with displaying the Doom II city sky for levels that originally had the animated fire sky in the PSX version. SKY3 from Ultimate Doom was converted to the new sky format for this version as well but never appears normally during gameplay (Stored as SKY03.CHR and SKY03.MAP). By switching around the order that the sky files are ordered in the system's memory will allow the previously unseen SKY3 to take the place of another sky texture.

I'm assuming that the Doom II Cityscape texture appears on the fire sky levels due to a simple programming error. The devs probably meant for the Inferno sky to take the place of the animated fire sky, but probably mistakenly point to the cityscape sky when loading in the level (SKY05 instead of SKY03 to %s.CHR and %s.MAP after P_LoadSectors).

I've also been looking more into why this version doesn't display colored lighting despite all the files and code still being in place:

- As mentioned in the previous post, Saturn Doom has it's own separate PLAYPAL file that it loads outside of the main IWAD. However when comparing this file with PLAYPAL extracted from the PSXDOOM.WAD shows absolutely no differences between the two files at all.

- Saturn Doom also has additional .PAL files for the fire sky that appears on the title screen, the title screen itself, the background of the cast sequence at the end of the game, the three legal/logo screens at the start of the game and unused files for IDCRED1 and IDLOGO. The aforementioned SKY20 and SKY21 also have .PAL files.

- I'm wondering since the LIGHTS lump wasn't included as it's own separate .PAL file could be a reason as to why colored lighting isn't displayed in-game, but it's only a theory at this point.

Finally as a random side-note, both DEMO3.LMP and DEMO4.LMP are identical files, which is why one of the demos appears to repeat itself twice.

1 hour ago, Mattfrie1 said:

- I'm wondering since the LIGHTS lump wasn't included as it's own separate .PAL file could be a reason as to why colored lighting isn't displayed in-game, but it's only a theory at this point.

No, it's because the game is rendered almost entirely by software and then put into the screen by the GPU. Just as in Vanilla Doom, and it limits the devs to the same old 256-color limit. Using colored lights like this looks absolutely horrendous so i guess that's #1 reason colored lights got cut.

EDIT: Wait no that's not the reason, i saw that video and there's full 16-bit (or 32-bit, not sure) color so that's not actually the reason colored lights got cut.

On 6/29/2019 at 2:30 PM, Mattfrie1 said:

- Level rendering appears to be handled in the same way as the PSX version as described on the last page, but instead of using quads the system is using distorted sprites to draw each individual column. This was a very common practice that Saturn programmers used in many 3D games on the system, and rendering of these sprites is handled by the Saturn's VDP1 graphics chip. Keep in mind however Saturn Doom emulation is still very buggy, so I'm assuming this is actually how the system operates and not a bug of the emulator.

I should note that "the system is using distorted sprites instead of using quads" is kind of erroneous thinking - the distorted sprites are the quads. I don't think any other means of rendering 3D geometry was used on the system (barring using the Mode 7-like effect one of the VDPs could do to a background layer - the Panzer Dragoon series used that one a lot to create vast expanses of things).

Also all of those graphics are typically paletted to my understanding, too; I'm guessing, but don't hold me to this, that there wasn't enough room in the Saturn's palette RAM to define all the colored lighting tints, so they just didn't bother. That said, perhaps I should poke at palette RAM and see what's actually loaded in there before I commit to this theory.

So now that the reverse engineered PSX DOOM source code has been released, can it be an even more progressive reference for the Saturn DOOM?

On 2/16/2020 at 4:45 AM, taufan99 said:

So now that the reverse engineered PSX DOOM source code has been released, can it be an even more progressive reference for the Saturn DOOM?

I'm hoping it can be. I've been trying to investigate how the dual CPU setup of the Saturn handles the rendering. From what I can tell so far, the Slave CPU remains dormant until entering a level and all the loading of a level into memory is handled by the main CPU. Editing any values accessed by the Slave CPU during gameplay cause the game to crash upon level startup or cause both the ceiling and floor to have a slightly glitchy appearance before crashing.

Even more interesting however I was able to disable textures by editing the IWAD in memory. The game will now display whatever sprites are stored in memory on the walls instead, providing some very interesting visuals. If anyone wants to chime in from [GEC] as to if this happens in the PSX version as well then I'd love to know. It's also interesting to see that sprites from previous levels seem to carry over into the next level loaded before getting overwritten by whatever is in the current level.

It should be noted that disabling textures does nothing to improve the framerate. I was also able to disable the sprites in-game as well in a similar method but this doesn't improve the framerate either.

Another nice discovery!

EDIT: Sometime in 2018, a user known as @Baratus II and his brother Trevor0402 attempted to make a Saturn DOOM TC.

Baratus II last visited Doomworld earlier this month, implying he's still sporadically active, but there has yet to be another news from their TC. Let's see if he will continue the development.

On 2/16/2020 at 3:45 AM, taufan99 said:

So now that the reverse engineered PSX DOOM source code has been released, can it be an even more progressive reference for the Saturn DOOM?

what kind of architecture is the satrurn exe format?

9 hours ago, Mattfrie1 said:

Even more interesting however I was able to disable textures by editing the IWAD in memory. The game will now display whatever sprites are stored in memory on the walls instead, providing some very interesting visuals. If anyone wants to chime in from [GEC] as to if this happens in the PSX version as well then I'd love to know. It's also interesting to see that sprites from previous levels seem to carry over into the next level loaded before getting overwritten by whatever is in the current level.

In psx it can always happen when a corruption happens in the memory of z_zone, here are some examples:

But in a normal way a missing texture would look like this:

1 hour ago, Erick194 said:

what kind of architecture is the satrurn exe format?

According to this site,

Quote

Sega Saturn Executables are actually COF/COFF (Common Object File Format) files which is a precursor to the ELF executable format that is used on most future console platforms.

I guess this means even more extra effort to work on it...

The program file for Saturn Doom is stored as 0.bin on the game disc.

On 2/18/2020 at 10:47 PM, Mattfrie1 said:

The program file for Saturn Doom is stored as 0.bin on the game disc.

I see... What about the code(s) inside it? How many similarities and differences does it share with the PSXDOOM.exe?

1 hour ago, taufan99 said:

I see... What about the code(s) inside it? How many similarities and differences does it share with the PSXDOOM.exe?

So far, there is quite a similarity between Psx Doom and Saturn Doom, it is a fact I have also started the reverse engineering of Saturn Doom. The first thing I am doing is locating and naming functions.

If we can make Saturn Doom run good, and devise a music engine to save disc space and everything and on loading times and everything, then the dream will be real.

On 7/1/2019 at 8:09 PM, Mattfrie1 said:

I've managed to somewhat fix the issue this port has with displaying the Doom II city sky for levels that originally had the animated fire sky in the PSX version. SKY3 from Ultimate Doom was converted to the new sky format for this version as well but never appears normally during gameplay (Stored as SKY03.CHR and SKY03.MAP). By switching around the order that the sky files are ordered in the system's memory will allow the previously unseen SKY3 to take the place of another sky texture.

I'm assuming that the Doom II Cityscape texture appears on the fire sky levels due to a simple programming error. The devs probably meant for the Inferno sky to take the place of the animated fire sky, but probably mistakenly point to the cityscape sky when loading in the level (SKY05 instead of SKY03 to %s.CHR and %s.MAP after P_LoadSectors).

 

Oh boy, I have been ages wishing someone could fix this, since it's so anticlimactic to play the Inferno levels with the Doom II cityscape skybox. In fact, I remember pointing out this issue ten years ago when I first visited this site regarding the urban myth of the Japanese Sega Saturn version when I got ahold of it, and even doing some attempts myself which got me nowhere. How can I exactly modify this myself? Is there some kind of patch I could use?

@Wesker If you have an Action Replay or other game hacking device for your Saturn you can input the following code that swaps the city sky with the unused Inferno sky. You can leave it active but it will have the reverse effect when you get to the Doom II city levels displaying the Inferno sky instead of the correct one, so make sure you leave it off if you aren't playing through any of the fire sky levels.

160769B0 332E
160769C8 332E
16076950 352E
16076968 352E

I've also been doing a playthrough of Saturn Doom again for the first time in a while plus some extra tinkering around with the Action Replay, I'll give my notes in a follow-up post.

@Mattfrie1 Nice discovery! I wonder if that code has never been known before...

10 minutes ago, Mattfrie1 said:

@Wesker If you have an Action Replay or other game hacking device for your Saturn you can input the following code that swaps the city sky with the unused Inferno sky. You can leave it active but it will have the reverse effect when you get to the Doom II city levels displaying the Inferno sky instead of the correct one, so make sure you leave it off if you aren't playing through any of the fire sky levels.

 

160769B0 332E
160769C8 332E
16076950 352E
16076968 352E

 

I've also been doing a playthrough of Saturn Doom again for the first time in a while plus some extra tinkering around with the Action Replay, I'll give my notes in a follow-up post.

Sadly I don't. I have a modded Sega Saturn console which allow me to load burned copies, so in this case I always prefer patching and burning a modified copy rather than relying on PAR codes. Is there any possible way to hardcode this into the game? And in this case maybe it could be done so the game would make a difference between the Inferno episode skybox and the Doom II city levels one.

If it's not really possible, then well, thanks anyway and I'll make use of them whenever I get an Action Replay or similar. By the way, are these codes the same for all the regional versions of the game? I have the Japanese and European versions. Would prefer applying it to the Japanese version because of the music arrangement order (I prefer it to the European and North American one) but would be fine with the European too. No interest for the North American version though, neither I don't have nor I'm interested on it as it lacks the link cable multiplayer feature.

15 hours ago, Wesker said:

Is there any possible way to hardcode this into the game? And in this case maybe it could be done so the game would make a difference between the Inferno episode skybox and the Doom II city levels one.

Not that I'm currently aware of unfortunately. There are a few other areas in memory that refer to the new VDP2 sky code but any changes to them cause the game to either crash or display the sky as all black.

15 hours ago, Wesker said:

If it's not really possible, then well, thanks anyway and I'll make use of them whenever I get an Action Replay or similar. By the way, are these codes the same for all the regional versions of the game? I have the Japanese and European versions. Would prefer applying it to the Japanese version because of the music arrangement order (I prefer it to the European and North American one) but would be fine with the European too. No interest for the North American version though, neither I don't have nor I'm interested on it as it lacks the link cable multiplayer feature.

I only have the North American version of the game so I'm not sure to be honest. But if you check those memory addresses in an emulator's memory editor and see the game files for the skies (.CHR and .MAP) nearby then they will probably work.

Then I guess I'll have to get an Action Replay or similar device. I know people tend to use these a lot for swapping region or even now for booting burned copies, but as I always relied on console modding, I was never really interested on them to be honest.

It appears that the link-up modes are still potentially compatible in the North American version of the game. I've managed to locate the area in system memory that handles main menu choices, and by setting one single value to either 0001 or 0002 will set the game into link mode with the on screen message about attempting to connect. As I've mentioned previously in this thread, most of the elements about the multiplayer link modes are still mentioned in memory (Intermission screen text, number of frags, etc.) so there is a good chance that the link cable is still fully functional but just simply had the option to select it removed from the main menu. Unfortunately Saturn emulation currently doesn't emulate the link cable and I don't own one to test this out on actual hardware, but if anyone reading this happens to have the capability to test this out please let us know. The Action Replay code to enter is as follows:

1604A2B0 0001 
OR 
1604A2B0 0002