Sega 3-D Glasses: How did they work?
Most individuals have two eyes, permitting for a stereoscopic view of actuality.[citation needed]. Nonetheless, video video games are typically designed to run on displays with a single display screen, seen from a distance, so three-dimensional results need to be achieved with perspective and different methods. However after all, some ways have been made to provide a real stereoscopic view; from the 3DTV fad of the early 2010s, to the Nintendo 3DS’ glasses-free parallax barrier. However how did techniques within the primitive days of 8-bit consoles do it? Let’s ask Sega!
Glasses
These are my Sega 3-D glasses. They’re in tough form; a earlier proprietor has cracked them, and changed the hinged arms with a scarf. However hey, they work!
And it’s not an enormous deal. In any case, if the injury bothers me, I can simply use these glasses; the Asus VR-100, from round 2000. They’re really the very same expertise, utilizing the identical 3.5mm port. And so they’ve received larger panels in addition.
Much more fashionable energetic shutter glasses aren’t that completely different technologically, however they typically used completely different connectors, and even wi-fi. However all of them do the identical factor. A sign despatched to the glasses tells one LCD panel, or the opposite, to “clean”, stopping the attention from seeing out of it. That is just about the identical factor as an LCD game, however even easier, since there’s solely two.
Sadly, I, uh, can’t discover my Sega 3-D glasses adaptor. I’ve been by means of a couple of strikes since shopping for it. Nevertheless it doesn’t matter, as a result of I’ve a Japanese Sega Grasp System! When you get an adapter to play western Grasp System video games on, this factor actually is the perfect console (for individuals who don’t wish to play Earthworm Jim (sprite scaling) or Dizzy (224-line mode), anyway) for the Grasp System, because it options the 3-D glasses inbuilt. Nicely, the adapter anyway. It additionally has FM sound.
The three-D sign
The glasses are, in a way, passive gadgets. Despite the fact that they’re known as “energetic shutter” glasses. That’s to say, they’re fully managed by the alerts despatched by the console. Liquid crystal wants an AC sign to activate or deactivate, and I’ve captured one of many channels on my oscilloscope. Sadly, the sign doesn’t work when the scope is linked to my pc (grounding points), so right here’s a horrible picture.
How does this get generated? Nicely, sadly, that is one case the place having the Japanese Grasp System is a draw back. Tracing the 3-D glasses sign on the circuitboard, we see it comes from a μPC324, an NEC chip which is made up of 4 op-amps. This amplifies and controls the alerts coming from the 315-5297 IO chip.
The 315-5297 is, so far as I do know, distinctive to the Japanese Grasp System. It generates the AC reference sign and a few controls to ship the proper sign down the op-amp’s strains; SMS Power has documented that. Discussion board customers there have additionally mapped out the discrete circuit used within the separate adapter, which is in the long run a easy oscillator.
The glasses adapter plugs into the cardboard slot solely to have a look at the system bus. When it sees a write to $fff8, it appears to be like on the low little bit of the bus and makes use of that to differentiate which eye’s glass must be enabled. It’s a quite simple system; so easy, the console really has no option to detect that glasses are current. It simply throws its writes into the void and hopes for the very best. (Nicely, really, they find yourself additionally being written to RAM at $dff8, however that occurs regardless)
And from a {hardware} perspective, that’s all that exists to help the 3-D glasses. Every thing else is as much as the sport code to determine.
Area Harrier 3-D
Area Harrier 3-D is just not my favourite option to play Area Harrier, even on the Grasp System. However let’s put that apart.
So, up-front, we all know the restrictions of the Grasp System {hardware}; like something that runs in a progressive mode on a typical tv of the period, it may solely run at 60Hz. (sure, 240p is faux and a lie, however shut sufficient for us) As famous above, the glasses work by selecting one eye at a time. So any sport goes to need to run at 30Hz. (25Hz for PAL varieties)
Now, 30Hz isn’t the worst; in spite of everything, it’s the body price of the interlaced video that a typical tv is designed to show. However don’t watch it with out the glasses on to get 60Hz! That’s a lot worse. If we take a look at a video seize of Area Harrier 3-D, we see that it exhibits every picture for every eye, one after the opposite. Issues that transfer extra from left to proper between the frames, find yourself being seen as farther within the background.
One factor concerning the Grasp System port of Area Harrier is that they use software program sprites. That’s to say, most of the shifting objects on the display screen– just about all the things apart from Harrier– aren’t really sprites, however are a part of the tilemap.
This causes them to maneuver a bit choppily and never have transparency with the background, however the tradeoff is that Area Harrier can have very massive objects with out flicker. In these video games, it’s value it. Area Harrier 3-D works just about the identical means.
Now, the issue with software program sprites on techniques just like the Grasp System and the NES is which you could solely write a sure variety of bytes to VRAM at a time, so altering quite a lot of tiles on each body generally is a drawback. This isn’t an enormous deal, although, as a result of often you possibly can simply decrease the framerate; since their place is restricted by the dimensions of an 8×8 tile anyway. However keep in mind, to be 3-D, it’s a must to swap all the things each body.
So how do you do that? That’s quite a lot of information to write down to VRAM.
Nicely, keep in mind when I said the next?
The tilemap of the Grasp System mode is surprisingly smaller than that of the NES; it’s 32×28 8×8 tiles as an alternative, or 256×224 pixels. Because the vertical top of the show space is restricted to 192 pixels, that is nonetheless effective for vertical scrolling. (There are 224 and 240-line modes on some later SMS fashions; in addition they develop the tilemap, and have been solely utilized by some European publishers late within the system’s life) Word that the tilemap eats into that 16kiB of VRAM.
That is, on the face of it, true. At any given time, the Sega Grasp System can show one tilemap layer. It’s 256×224 pixels massive and made from 8×8 tiles, and takes up 0x700 bytes within the Grasp System’s 16kiB of VRAM.
And that is all true. Utilizing the emulator Emulicious, we will visualize the VRAM. Right here it’s for Area Harrier, the unique, non-3D model.
Discover that it’s virtually fully made up of tiles which might be utilized by the tilemap and sprites. However there’s an space on the backside of the display screen, at $3800, the place the tilemap is. (After which, at $3f00, the sprite information)
But when we take a look at Area Harrier 3-D, it appears to be like just a little completely different.
Issues are organized fairly in another way. However most notably, the realm of tiles and sprites is twice as large. How can this be true, if the Grasp System has just one tilemap?
The Grasp System solely has one tilemap at a time. You see, whereas virtually each Grasp System sport has its tilemap (“title desk”) at $3800 and its sprite desk at $3f00, that’s not required. There are two VDP registers that allow you to transfer it to different factors in RAM.
It is a function relationship again to the TMS9918A VDP. Whereas computer systems and sport consoles typically paired the VDP with 16kiB of RAM, the datasheet mentions that it may help RAM as little as 4kiB. On this case, it’s very handy to maneuver issues round, and never have mounted addresses. This kind of factor is the distinction between a extra general-purpose chip just like the TMS9918A, and single-purpose chips just like the NES PPU. (The Grasp System VDP is a single-purpose chip, nevertheless it has heritage, damnit)
So Area Harrier 3-D offers up some tile house to as an alternative keep two copies of the title and sprite tables, and shifts between them every body. You continue to have to add twice as a lot information to VRAM as with one display screen, however you don’t have to redraw the entire display screen each body, simply the adjustments. From my testing, each 3-D Grasp System sport makes use of this screen-flopping technique to a level, although some solely flip the tilemap and never sprites; and Poseidon Wars 3-D solely makes use of the tilemap flipping for the HUD in gameplay.
And keep in mind, that is the bottom Grasp System {hardware}. Any sport that’s prepared to surrender the tile house– an enormous sacrifice– could make this tradeoff. Right here’s the title display screen of Double Goal, the Japanese model of the sport we received within the west as Quartet. I’ve the Japanese model as a result of it has significantly better field artwork.
That cool smooth-scrolling may in all probability be achieved with an elaborate set of sprites and cautious timing, however as a result of they may spare the tiles, they as an alternative simply saved two title display screen nametables in VRAM, and use the Grasp System’s line interrupt to change between them as-needed whereas the display screen is being drawn.
Right here’s the nametable at 0x3000 for Double Goal:
And right here it’s at 0x3800. Apparently, it really has many of the character artwork current nonetheless, however makes use of a unique palette (the one often used for sprites) to cowl them up.
It’s a fairly neat trick, for those who can spare the VRAM. The Grasp System might not be capable to do video bankswitching just like the NES, however this kind of factor permits some related results, with quite a lot of flexibility, because it’s all in RAM.
Taking part in on LCD
So that you may need observed that I discussed that 3DTVs used the identical energetic shutter approach. It would make you marvel, why don’t the 3D glasses work on LCD TVs, then? Even with a low-lag upscaler?
The reply is that there’s at all times some lag on an LCD. The 3D circuitry in a 3DTV is a part of the LCD, and due to this fact can know precisely when the LCD will show a body. Sadly, the Sega Grasp System is simply as restricted. In concept, although, I suppose for those who had the programming ability and an upscaler and show with a continuing, identified lag, you would change the sport to time correctly. Good luck…
An alternative choice is to play on a really dangerous upscaler. 3-D video games alterate 240p frames on each discipline. Due to this fact, upscalers designed for solely 480i video content material will simply interpret them as interlaced, and mix the 2 frames collectively.
Discover that objects which might be additional away find yourself duplicated. This makes oncoming objects seem as two components that merge collectively as they get shut; your bullets do the alternative, splitting into two as they transfer into the gap. Whereas it’s surprisingly playable like this, if that is the one means you possibly can play it, do your self a favor and persist with the primary Grasp System Area Harrier. You don’t want the 3D model’s FM soundtrack that badly.
In fact, you’ll additionally get the downsides of low-quality upscalers. Nonetheless, quickly switching to create a faux interlacing impact is how my nightmare cartridge produced these high-resolution skulls, in case you questioned.
In the long run, if you wish to play Area Harrier in 3-D with the objects actually coming at you, it’s this or the Japanese-only Nintendo 3DS port. And even at 30fps, that’s nonetheless a fairly cool impact. Simply be sure you even have the glasses.