NewsNintendo 3DS

Emulating MegaDrive On 3DS Isn’t Easy – Enter 3D Sonic the Hedgehog!


Originally posted May 15th, 2013 on Impress Watch. Siliconera is coordinating with SEGA to share these in-depth interviews about classic games like Sonic the Hedgehog and the Sega MegaDrive. Translated by SEGA. Edited by Siliconera.


Pictured: Naoki Horii, President, M2 (left), Yosuke Okunari, Producer, SEGA CS3 (right)


MegaDrive is difficult on 3DS VC, so enter the 3D Remaster Project!


Yousuke Okunari (below, YO): So far with the 3D Remaster Project, we’ve put out Space Harrier and Super Hang-on. People might have been looking forward to another arcade cabinet game port, but our next release is actually a stereoscopic 3D adaptation of Sonic The Hedgehog.


As we discussed in our previous interviews, our previous two releases were games where the player “scrolls into the screen”, something easy for anyone to imagine in 3D. But for the next game, we wanted to put out a game that people wouldn’t expect to see in 3D. With that in mind, we considered multiple titles and in the end we chose Sonic’s debut game, because there’s nothing more SEGA than that.


Still, it took us awhile to settle on Sonic. First, as you may know if you’ve been following the interviews, there was quite a bit of time between when the 3D Remaster Project first started and when 3D Space Harrier was released. This put us essentially around the time when development had just started on Sonic Generations, which later released for the PS3/Xbox360. Generations included a completely 3D version of the Green Hill Zone stage which replicated the original very well and also included support for stereoscopic 3D.


So right then, there were some inevitable doubts about whether there was any point to re-making MegaDrive Sonic, and if a remake like that was needed. However, we came to the conclusion that “building something in 3D” and “taking something that was drawn in 2D and making it 3D” ultimately resulted in two different experiences, so we decided to move forward with a 3DS port.


Naoki Horii (below, NH): So when you asked us if there were any MegaDrive games we could remake in stereoscopic 3D, SEGA had already started development on Sonic Generations?


YO: That’s right.


NH: Interesting that Sonic survived the cut then.


YO: Once we’d decided to restore SEGA titles with stereoscopic 3D, I actually wanted to do some home console games as well. So when M2 and the North American and European SEGA staff decided on the lineup of games for the 3D Remaster series, which included Space Harrier and Super Hang-on, and removed Thunder Blade (laughs), Sonic was one of the titles on the list.


We started Game Gear development for Virtual Console at the same time that work on the 3D Remaster Project was going forward, and I was of course asking M2 about whether we could bring titles on SEGA hardware other than Game Gear to Virtual Console. When I talked to them about it, M2 told me “MegaDrive games probably won’t work out…”


…And now, Sonic is up and running. (laughs)


NH: You’re leaving a lot of the story out. (laughs) The 3DS had a big change in architecture from the Nintendo DS and Game Boy Advance; it uses a GPU that specializes in stereoscopic 3D. When you bring software from an era when games were composed of sprites and backgrounds into an emulator on the 3DS, you wind up doing a lot of work in a very roundabout way. And that offsets the performance gains you get with the CPU. That’s why I said “they probably won’t work out.”


YO: So from the outset I was hearing that MegaDrive games on the 3DS would be hard.


NH: The MegaDrive for instance has two background layers and four pallets (color definition tables).  Replicating that is the tough part.


Footnote: The Game Gear and the MegaDrive
Game Gear – CPU: Z80 CPU. VRAM: 16k bytes. Sprite Count: 64. Screen Resolution: 160×144 pixels. Sound synthesizer: 3 channel PSG, 1 channel for noise.

MegaDrive (Genesis in North America): CPU: MC68000 and Z80. VRAM: 64k bytes. Sprite Count: 80. Background Layers: 2. Screen Resolution: 256×224 pixels. Sound synthesizer: 6 channel FM Synth and 3 channel PSG, 1 channel for noise (one FM channel can be used for PCM)

Game Gear inherited its architecture from the Mark III and Master System, while the MegaDrive was basically a down-sized version of the arcade version of Space Harrier (single main CPU, able to display 2/3 the sprites compared to the arcade version, no scaling support)


YO: We had intended to get Game Gear games on Virtual Console from early on in the 3D Remaster Project, but I had to think over our approach for the MegaDrive titles, since we’d put them on the backburner after we were told that the games wouldn’t run on 3DS. One way was to use the ‘copy by eye’ method, where you rebuild the program from scratch but it looks exactly the same to the player. I figured M2 wouldn’t want to do it that way…but on the other hand, emulating the titles was going to be hard.


NH: I think the problem was that we didn’t have time to build a ‘copy by eye’ in the first place…


YO: Creating a ‘copy by eye’ does indeed take time. Not only do you need to do a complete analysis on the game from top to bottom to ensure that it’s accurately reproducing the original, testing takes ages because you have to make sure all the little hidden tricks in the game are in, and it’s easy to miss things that don’t run the same as the original.


NH: It’d be much quicker to make a Gradius ReBirth1 than remake Gradius by eye. (both laugh)


YO: Anyways, since this is supposed to be a “Remaster” project, we were in a bit of a bind. Horii-san had said “the games won’t run”, however he came back and told me “but there’s a way to make them run.” The same thing happened when we started on the SEGA AGES 2500 series for PlayStation 2. The typical emulation methods didn’t work at first, but after a while we were able to get a MegaDrive emulator running on the platform. He told me: “If we use the same approach, we might be able to get MegaDrive games running on 3DS too.”


1. Gradius ReBirth is a WiiWare title developed by M2 and published by Konami in 2008/2009.


NH: It’s not quite the same approach. The point was that if we struggled with it as much as we did for the PS2 games, it might work. Doesn’t have a damn thing to do with the approach. (both laugh)


Did you wind up cutting MegaDrive features that weren’t being used in the game?


NH: We cut some of the fat, accelerated things by writing some assembly code and whatnot. However for the 3DS remakes, we wanted to effectively utilize the 3DS’s CPU resources as much as possible, so we wrote assembly where we needed assembly, and swapped out code as needed from the emulator, which was written in C. This took quite a bit of time, and turned into quite a magnificent bit of work. So we had to slowly cobble together performance speed by doing things like writing code that more easily hits the cache every time it’s called.


YO: It’s M2’s policy that any input lag is out of the question, which means they have to get the control response as close to the original as possible. Since that’s a project pillar, speed becomes a very complicated and important aspect of the program. They invested a lot in this point for the PS2 version, and the same amount of struggle went into the 3DS version as well.


NH: The older I get, the more exhausting it is. (laughs) I definitely have a hard time pulling all-nighters anymore. (laughs)


YO: So in the end, we decided not to do any straight MegaDrive ports for [3DS] Virtual Console. However, we figured that if we put in more resources and time than we would for a typical Virtual Console game, added in bonus content, and brought it to the table as a 3D Remaster Project title, then it might be worth doing. So we moved forward with several MegaDrive projects.


The never-ending battle with slowdown.


YO: That said, after starting development, we immediately ran into problems. Unlike games like Space Harrier, which were built in 3D from the very beginning, the difficulty of converting a 2D game into 3D was on a different level. In order to give this an easy explanation, I’ve brought along the first version of the game we got working on the 3DS. Take a look. This is the prototype for 3D Sonic The Hedgehog. With this version, you can play from start to finish like you normally would.


Since the MegaDrive has two backgrounds layers and some sprites, the initial idea was to add depth information to the background portions, and then place sprites with depth info right in front of you. We thought that by doing so, the game image would come out in stereoscopic 3D. However, when you put the game in 3D like this, the screen looks empty. Compare it to the final version and you can see that the rasterized portions of the backgrounds look quite different. I wonder if the people reading this will get the picture. (laughs)


The rasterized portions of the background in this first version don’t have depth information yet, right?


YO: That’s right. When we played the initial version, we found that playing it in 3D didn’t really add much impact or appeal. Even though we’d got it running, we even started to think to ourselves, “maybe this isn’t going to work. Maybe we should just give up on Sonic.” Since Sonic was the flagship game for the MegaDrive, it would need to have a new aspect of fun to it in 3D… but the initial version was just a simple implementation of the 3D. We DID get it working, but the fun wasn’t there yet. Especially the first stage, Green Hill Zone, didn’t feel 3D and thus wasn’t very exciting.


However for the loop-de-loops in the stage, there were places that would have broken the 3D effect when you look at it which M2 told me they had fixed by patching the original code. In other words, M2 had gone in and applied 3D processing to those parts of the level by hand.


Some trees are in the background and some in the foreground. In the screenshot on the left, you can see Sonic overlapping the flowers in the background and running behind the tree in the foreground. On 3DS, these flowers look like they are blooming in the background. On the right, we have a similar tree. It’s positioned behind behind Sonic.


As we discussed that approach, M2 mentioned that while they were researching stereoscopic 3D, they found that if they applied 3D processing to areas of the stage that use parallax scrolling backgrounds2, it looked amazing. So I said, if that’s the case, maybe we should add depth to the clouds, the ocean and all that. M2 told me that doing so was certainly possible technically, but it was going to generate processing overhead, and require a fair bit of work. Still, I felt like we definitely had to do it, so I kept bringing it up.


What’s more, to keep the game speed up, they hadn’t yet implemented the FM Synth emulation. Every time the FM Synth made a sound, the program would generate slowdown, so it was as if I was asking them to make it lag even more.


A 3D-compatible Virtual MegaDrive: the Gigadrive Plan.


Something I was curious about when you mentioned how hard it was to get MegaDrive games to run on the 3DS was that, compared to the PS2 port,, it sounds like you have to squeeze out twice the framerate (60fps to 120 fps, 60fps x 2 eyes (left and right) = 120fps), all while not having any input lag. That sounds like a really tough goal, right? It’s a pretty amazing feat.


NH: Around the time we were building Super Hang-on for SEGA AGES ONLINE3, Okunari-san told us to “make everything 3D,” so we put a bunch of different games into 3D and showed them to him (refer to the 3D Super Hang-on interview). At the time, we’d actually built a development environment that allowed us to make and show off quick implementations of stereoscopic 3D at a pretty low cost. We figured we’d just run the same program on the 3DS and that’d be good enough. However on the 3DS, a lot of things weren’t working (depth adjustments we’d made to the background and sprites were broken), so at that point, we knew going in and fixing each issue one by one would be no small task.


2. Parallax scrolling is a technique where multiple images are scrolled horizontally at different speeds to give the impression of depth to the screen. While there are a few ways to do achieve this, the MegaDrive used a method called raster scrolling, which is specifically what Mr. Horii is referring to.
3. Released as Sega Vintage Collection 3 overseas. Remastered version of classic SEGA titles for PlayStation 3 and Xbox 360.


Let me give you an example. When you add binocular depth to the game (by creating two separate screens, one for the left eye, and one for the right), you tend to lose the right and left edge of the screen, since you can’t add art that never existed in the first place. Fixing little issues like this one by one gets pretty overwhelming.


Once we had decided to include depth in rasterized areas, we figured we might as well build a MegaDrive architecture that supports stereoscopic 3D, a new SEGA console we dreamed up, which we decided to call the “GigaDrive.” We figured that if we can build this new platform on the 3DS using emulation techniques, and then create a version of Sonic The Hedgehog that runs on it, all our problems would be solved! This would give us smarter and more flexible 3D compared to patching the MegaDrive game program. In that sense, you could say we’re just “patching” a patch for a GigaDrive game, which gave us a lot more latitude to work with.


So that changed your approach to the port.


NH: That’s right. But at that point we still had no idea if the thing was going to work. (both laugh) Inside this “GigaDrive”, we increased the number of background layers to four, gave each layer a Z-value (depth info), and gave each raster line a Z-value which allowed us to for instance, knock the lake into the background. Funny because I was just mentioning how hard it would be to port the game since the Megadrive has two background layers. (both laugh)


Depth was added to the clouds on this stage as well. Note that the Japanese version has parallax scrolling for the sky, but the overseas version only has one background layer.


I see what you mean.


NH: So, rather than patching a MegaDrive game, we approached the project with the idea of porting the game to new hardware (which was already running on the 3DS).


Would that let you port the graphic-related data as-is?


NH: Yes, and we can also port over the game’s main routine.


I guess that means you’re saving processing load at a lower layer then?


YO: All of these struggles with the code came about because of my irresponsible request. But after a while, they managed to get depth showing for the rasterized portions. At that point I felt like the effect was looking pretty good. In the stages after Marble Zone (Stage 2), there’s quite a bit of rasterized imagery, and once they made those areas 3D, I felt like the approach was going to work. We had finally seen the light at the end of the tunnel. However, starting from this version the game speed dropped below 100%. (laughs)


The clouds in the sky also have depth. In addition, having parallax scrolling on the sky was only present in the Japanese version, so in the overseas version (which doesn’t have parallax scrolling), the sky was simply one background image displayed in the back.


NH: Yeah, we were consistently losing about two frames of processing.


YO: Now there was one bit of 3D processing M2 had included which I didn’t ask them for. It was the depth effect between Sonic and the trees in Green Hill Zone. You might not notice it when you play the MegaDrive version, but there are actually two types of trees there, ones in the background and ones in front of Sonic. M2 added depth difference to them. Which meant that suddenly it seemed like the area Sonic was running in had real depth. I said, “hey this is amazing, let’s use this,” at which point Horii-san looked at me with a deeply serious face and said, “On every stage?” (both laugh)


NH: Of course I did! I mean, we’re talking about EVERY STAGE! (laughs)


YO: Which means more processing load. And on top of that, since this was on the GigaDrive, it all of course had to be done by hand.


Depth effects were created in the original game by just changing the sprite draw priority rendered on the same layer. But once you assign depth values to those sprites, you’ve got something completely different, right?


NH: That’s the gist of it.


(smiles) And you’ve got to assign priorities one by one, right?


NH: One by one. And of course it’s different for each stage.


I see…


YO: The last bits of 3D we added in were the electric lights and construction signs in Starlight Zone. There are some that are brighter and some that are dark, but this depth is baked into the graphic.


NH: We wanted to realize what the original graphic artist for these objects wanted to do. …and also everyone points it out, so we wind up doing it.


If you look carefully at the lights, some are bright and some dark. When viewed in 3D, they are of course shown in the background. The metal scaffolding on the right is in the foreground and thus is in the very foremost layer. In the right-hand screenshot, you can see a difference in depth for the warning signs.


In the left screen, the object in front of Sonic is in the background, and the one behind him are in the foreground.  In the right screen, the 3D positioning of the red cone objects are implied by the way they’re lit.


In other words, since there are already objects that that feel like they have depth to them in the game it wouldn’t feel right if depth information wasn’t assigned to them… It seems that the original team on the MegaDrive was trying to create visual depth by using objects that are alternately lighter and darker. So when you remake the game 3D, they’d look off without depth information.


YO: These are the kinds of things that slowly build up as we argue over the details, even though we have to keep the game speed up…


(laughs) So does adding depth increase the background layers?


NH: We added four background layers, and that’s a lot to process already, but changing the depth info on top of that adds even more processing and slows down the program. From the start, before we even thought about maintaining the framerate we were already short on processing power. So as we added things, we made speed improvements along the way.


On one hand, you’re adding things that require more processing, and on the other you’re doing your best to reduce the processing load. Sounds like this project was also a constant struggle.


YO: For Space Harrier and Super Hang-on, the games themselves were built in 3D from the start, so all we had to do was add 3D based on the program itself and that was it. However in Sonic’s case, 3D depth data didn’t exist, so we had to survey the art and add depth as appropriate. Also, when you turn off 3D, it has to look just like the original MegaDrive version. The differences between the two are pretty interesting.


NH: With Sonic The Hedgehog, I think we’ve gotten the game to the level where if you went back and played the original, it feels like Space Harrier does, like it was built in 3D.


YO: Building Sonic like this, I feel like you guys really boosted your tech for porting MegaDrive games to the 3DS.


NH: Absolutely. Just looking at the finished game, you might not think we struggled much with it, but really the whole thing was a struggle. It all comes down to one thing: Adding priority to sprites that have depth, even if they’re part of the same graphic.


YO: It’s like they say in the animation industry: “We spent days on a 5 second cut.” (laughs) That’s very much M2’s style, and it’s what it took to get stereoscopic 3D working.


Simply adding the Spin Dash does not a finished job make.


So what’s the ‘Special’ addition to this game?


YO: Alright, let me introduce some of the game design changes we made for the 3DS version. Looking back at the release of 3D Space Harrier and 3D Super Hang-on, one thing that we were concerned about was the game difficulty. So for this game, we went in and implemented stage select as a standard feature, i.e. the one that was included in the MegaDrive version as a cheat code. If you turn ‘Special’ on from the very beginning, you’ll be sent to the stage select screen when you start the game.


Originally, you could go to the stage select in the MegaDrive version by inputting the cheat command at the title screen, but since it was a cheat code and Sonic being a twenty year old game, we figured we should just make it a standard feature. The ‘Special’ setting is off by default, but if you turn it on, you can play from any stage you like the first day you buy it.


The original (Japanese) manual and advertisements for Sonic The Hedgehog mentioned that the game had “a variety of stages.” Because of that, lots of people, including myself, played hard to get to the next stage. But the first game was pretty hard, with stages like Marble Zone (Stage 2) and Labyrinth Zone (Stage 4), and I think some folks probably gave up on the more technical stages. If the same thing happened in this version, you wouldn’t get to experience the fun of running through some of the later stages in 3D like Star Light Zone, which M2 has spent a lot of time on. And that would be a bummer.



In 3D Sonic The Hedgehog, not only can you switch between the Japanese and International versions, but you can also use the Spin Dash, which was never available in the original MegaDrive version. The Spin Dash graphics come from Sonic The Hedgehog 2.


At the time, I probably didn’t give it any thought, but now that I think about it, there is a lot of stuff in this game.


YO: We’ve made the stage select a standard feature because we want players to see every stage, and for the people who gave up on the original to come back and give Sonic another try. One more thing is the Spin Dash. This was actually a lot of work to put in. These days, everyone knows the Spin Dash from modern Sonic, but it wasn’t in the very first game. So when people go to play the first game, they’re like, “Wait, what?” (laughs)They always try to Spin Dash right away.


The only version that included it was the version included in Sonic Jam for the Saturn. You can use the Spin Dash in that version, so when I asked M2 to put the Spin Dash in, I brought the program source along with me. (laughs)


I see. (laughs)


YO: But Sonic Jam4 was a Saturn-era game, so it wasn’t running Sonic The Hedgehog via emulator.


NH: First off, we wanted to find out if there was some data in Sonic Jam that resembled the MegaDrive version of Sonic The Hedgehog, and if there was, we could just do a comparison to the original game, note the differences, and analyze them. But as we got deep into the code, we realized “there’s nothing like that here at all”, and that’s where the story starts.


YO: M2 told me: “we looked over Sonic Jam’s source code, but we don’t get it.”


NH: Well, it wasn’t so much that we “didn’t get it” but rather that looking through a couple gigabytes of data and picking out what we need would be super exhausting. So I asked Okunari-san, “We need to know where to start looking, so please let us talk with the original development staff.”


4. Sonic Jam, for the Sega Saturn, featured a version of Sonic The Hedgehog that had Spin Dash.


YO: I immediately went to Takashi Iizuka, the head of Sonic Team, and asked him who worked on that portion of the game, and he told me, “Oh, Yuji Naka did that part.” His name was in fact in the credits, despite being a department manager at the time. (laughs) So Yuji Naka himself added Spin Dash as a “fix” to the original MegaDrive version… I had no other options, so I wound up sending a mail to Naka-san, who is now the president of a company called Prope, and asked, “Sorry, but could you let us know how you added Spin Dash to the game?” And he replied with some sage words of advice.


Oh, wow!


NH: There was a nice explanation and he basically said “It’s easy, give it a shot.” Which makes you go: “Easy!?…what the…” you know? Man, people from that era are really amazing. But thanks to his help, we were able to get the Spin Dash implemented. Still, it’s not like we just put it in and it worked perfectly. No, once we started playing with it, we ran into places in-game where we had to question whether it even worked with the game design. Once it was implemented, there was a ton of things to check.


YO: When it was first implemented, there were no animations or graphics for it. Since the action wasn’t in the original, the graphic wasn’t either.


NH: Sonic The Hedgehog already nearly maxes out the MegaDrive’s VRAM, so when you’re told to add in Spin Dash animations on top of that, you don’t have much space to work with. That’s when we decided that our new virtual platform, this thing we were calling the GigaDrive, needed a VRAM extension.


YO: After that, we were able to pull graphics and animations from Sonic The Hedgehog 2 and add them into the game. The next problem we ran into once the Spin Dash got implemented was that since it wasn’t an action in the original, there were places in the game where you would wind up flying off the screen and dying.


I sort of panicked, and was saying “oh, this is bad,” to which M2’s programmer said: “well, what’d you expect?” So I went back to Sonic Jam to see what they had done, and it turned out they’d addressed all those bugs in their version. That’s when we realized that we’d need to bring in not only the move’s action itself, but all the bug fixes from Sonic Jam that went along with it as well!


Wait, so you mean that the Sonic The Hedgehog in Sonic Jam wasn’t using the original MegaDrive version’s data?


YO: No, it was based on the original data.


NH: It’s doesn’t run on an emulator; I think the original code was most likely adapted for the Saturn. It’s similar to how people got arcade games running on the X68000. It was a pretty common approach for titles in the latter half of the Saturn’s lifecycle. This is also similar to the method used to run Space Harrier on the Super 32X.


So the changes made to the Sonic Jam version were useful as a reference point?


NH: Yes they were.


YO: The programmer at M2 knew early on. In an interim version of the game, I got really excited that the Spin Dash was working but he pointed out to me: that “yeah, it ‘works’, but that’s all it does…” Anyways, after a bit of a process and before I knew it, the Spin Dash had been implemented perfectly. Although it was really pushing up against our deadlines…


NH: You know, Okunari-san touched on this earlier, but since people assumed that the Spin Dash would be included by default, once you implement it again, they wind up thinking “well of course I can Spin Dash”.  Whereas it’s something we were pulling our hair out over…


YO: Yeah, after M2 worked so hard to get the move in, they told me they wanted to make the Spin Dash the game’s “Special” feature. But I said, “No no no, in this day and age, people expect the Spin Dash. We should just slip this into the main game.” No one’s likely to turn off Spin Dash, other than those who just really want to play the complete original version. Not nowadays. So we quietly included the option to turn Spin Dash off in the back of the system options.


NH: And I was fine with that… Okunari-san always comes to us with these sorts of proposals, and we’re more than happy to implement them. But then… when we tell him, “Hey, um, you know this is going to take a while, right?” and start talking deadlines, he’ll tell us: “The deadline is iron-clad. If it’s not going to make it in time, then we don’t have to implement it.” That’s the spiel, but somehow every time, the changes make their way in…. Okunari-san has a lot of opinions that come from him personally, and not from a producer perspective. And I think that’s without a doubt been key in maintaining the quality of the 3D Remaster Project.




YO: As a result, they’ve managed to make 70% to 80% of the reckless ideas I throw at them happen.


NH: So when he says “Don’t do it if it’s not going to make it in time,” that’s generally what winds up happening.


The 3D Remaster Project moves forward!


YO: Thanks to this support, Horii-san’s “GigaDrive” steadily presses on.


NH: From M2’s standpoint, since we’ve gotten away from the original plan to emulate the game in 3D, and instead wound up creating an extension of the hardware spec that makes it easier to put MegaDrive games into 3D, we think of the GigaDrive as an ‘unofficial’ new SEGA console.


The specs are very clearly defined, and someone out there with enough skill could make probably make the same hardware. That’s the level at which we’ve built it. In other words, if you (virtually) popped in a GigaDrive cartridge, you could play Sonic in 3D, and if you took an old MegaDrive cartridge and put it in, you could play that too; we’ve built it with that type of cross compatibility in mind.


Personally, this is something I care deeply about. I don’t know how people would react when they hear the word “GigaDrive”, I don’t know if they’d say “Huh? …what’s that?” or get totally hyped about it, but I’ll send you a spec sheet, so you can check it out for yourself. (laughs)


GigaDrive (aka Super MegaDrive) Specs, Draft v1.0.
In a fictional version of the early 1990s where 3D TVs have proliferated, M2 has finalized the specs for an imaginary 3D TV-compatible SEGA game console, the GigaDrive. The 3D MegaDrive, which will subsequently be released by SEGA, will conform to these imaginary hardware specs. While highly unlikely to ever see the light of day, in the off chance that it does, M2 has taken careful consideration to ensure backwards compatibility with MegaDrive cartridges. In this era, once 3D MegaDrive titles popped up, a fair selection of games were released for the GigaDrive.


Hey you!! Why not give SEGA’s new imaginary console a test drive with 3D Sonic?


* Please note the specs below are in draft form. There will be changes in subsequent revisions.
■ The GigaDrive supports backward compatibility with MegaDrive games (Unmodified MDROMs will run normally without modification)

・Expanded VDP register for controlling expanded functionality included

・Expanded VRAM included

・Four extra background layers included

・Z-values can be set for each extra background or raster line

・Every sprite has a Z-value setting.

・VDP and Expanded VDP registers are memory-mapped and accessible

・VRAM and Expanded VRAM are memory-mapped and accessible


* Memory Map


* $c00000 r/w VDP DATA

* $c00002 r/w VDP DATA

* $c00004 r/w VDP STATUS(read)/CTRL(write)

* $c00006 r/w VDP STATUS(read)/CTRL(write)

* $c00100-$c0012f -/w VDP REGS(write only)

* $c00130-$c0015f -/w EXT VDP REGS(write only)

* $c00200-$c0024f r/w VSRAM

* $c00300-$c0030f r/w DIPSW

* $d00000-$d0ffff r/w 64KB VRAM

* $d10000-$d1ffff r/w 64KB EXT VRAM

――Detailed I/O Map spec omitted――


YO: It’s their layout of what a powered-up MegaDrive would look like.


NH: I thought it would be pretty awesome to reproduce the ultimate MegaDrive on the 3DS. To keep the MegaDrive atmosphere intact, we made no changes to the art palettes. There are still four.


We did expand the background layer count by four…  two each for the left and right eye. And these can hold Z-values for each render line. Sprites have Z-values as well. And, since there wasn’t enough VRAM for 3D Sonic The Hedgehog, we expanded the VRAM by another 64Kbytes, to twice the size of the original MegaDrive. With just a little more pushing, maybe we could actually build some hardware with it. Not that SEGA would sell it for us though. (both laugh)


YO: Well, there wouldn’t be any software for it, right? (laughs)


NH: Yeah, there wouldn’t be. We’d of course be happy to make some ourselves though. Incidentally, when I told people at the office that Project GigaDrive was our next project, they all started using “GigaDrive” in their weekly and daily reports, and getting really involved in the whole idea. So internally at M2, I think it’s been a really good thing. Maybe in a couple of years, we can get Power Drift running on it and put that out. (grins) That’d be cool.


With regards to the GigaDrive’s architecture,  what level of hardware are we talking about?


NH: We’ve expanded the flexibility of the MegaDrive, to a larger extent than for instance how the PC Engine Super Grafx multiplied the number of sprites and backgrounds that the PC Engine had, and added memory to it. With the GigaDrive, Video Display Processor functions were added for the expanded game functionality, there are more sprite tables, you can use six background layers, the backgrounds have depth, all objects have depth, etc. Once you’ve got all this working, you can build Sonic The Hedgehog in 3D.


YO: Honestly, since we were really maxing out the specs, there are a few things that we cut compared to 3DS Space Harrier and 3D Super Hang-on. One is widescreen support. We haven’t done anything to show what would be outside the normal screen, partly to maintain the game balance of the original. We also wound up not adding a frame around the game screen.


NH: We really wanted to put in a TV frame. But if we did, there wouldn’t have been enough processing power to handle the stereoscopic 3D. Since that’s another thing we’d have to draw, we gave up on it. Instead we added “Classic Mode” as an additional 3D mode, where we were able to replicate a CRT TV in 3D. This mode is pretty nice. Hopefully you’ll agree that it looks like an old TV. The graphics blur too.


In the screen settings menu, you can choose from Normal or Classic. In Classic mode, the screen curves just like a CRT TV screen, and the colors blur together similar to how they do on a real TV.


YO: Other companies have done the same thing, so you might think, “Oh, I’ve seen that.” But if you look really hard, you can see how the colors blend.


NH: It blends like it would if you’d hooked up a console with composite cables. The red blends a little less than a real machine. Give it a shot when you have a chance.


YO: Yeah, it does a good job of replicating that sort of fuzziness you see with the MegaDrive over a composite connection.


Does the process take a normal screen and apply a filter to it?


NH: That’s right. Well, it’s more like a shader than a filter.


So you’re adding processing when the screen’s being rendered.


NH: Correct. Which means we just barely get everything into memory, and that’s why we weren’t able to include the CRT TV frame. We struggled on that one.


YO: We also weren’t able to include full screen support or replays. That’s how hard it is to get MegaDrive games running on the 3DS; it was more challenging than porting an arcade game.


NH: Well, we could have got the TV frame in if we’d cut the stereoscopic 3D. (laughs)


YO: Although the additions to the game wound up being a little simple, we were able to get the MegaDrive Sonic The Hedgehog running perfectly on the 3DS, and with 3D to boot. So we slotted it in our line up as release #3. That said, you can’t really get an idea of the 3D in this game from screenshots, even more so than 3D Space Harrier, which is a little frustrating. For those who want to see how the 3D turned out, it’s only 600 yen, so please buy it and give it a shot. I want people to see it in motion.


Yeah I hope people check out the 3D effects on the rasterized parts of the game. People who were really impressed with the raster scrolling effect back then would love it. For those who have played the MegaDrive release, it’s kind of like a treasure hunt trying to find spots that are different from the original.


YO: The 3D makes you want to climb to the top of the stage just to look into the background. It’s the same game you played back then, but it looks completely different. In that way, I suppose it’s kind of like 3D Space Harrier. This year is the 25th anniversary of the MegaDrive, so I think it’s great that we’ve released Sonic in a milestone year like this.


NH: Parallax scrolling was often used by taking backgrounds and overlapping them with the intent of giving the impression of depth, so it’s perfect when you put it in 3D.


It’s pretty crazy to think that those backgrounds now have Z-values.


NH: Yeah. It shows you that if you spend time on something, you can work out the problems.


YO: I just give the orders.


NH: You also need time. With every project, I always think “if only we had more time.” (laughs)


YO: Since we now have the MegaDrive architecture running on the 3DS, we will be using it as much as we can going forward. However, some games work well in 3D and some don’t, so we have to consider whether we can remake them in 3D within the standard development timeframe for a downloadable game. For example, Landstalker would be an incredible game in 3D, but it has a lot of stuff that looks 3D that are actually 2D. For that reason, it’d be faster to just build it again from scratch than remake it in stereoscopic 3D. It all depends on the work involved and whether the game will sell, you know? Unlike Virtual Console, these aren’t just ports. They’re hand-made 3D recreations, and since we have to consider whether they’re worth the effort, it’s always hard to choose what to green light.


Oh, now that you mention it, when the 3D Remaster Project website was updated for 3D Super Hang-on, two more spots opened up. People were wondering if that means four titles will be released in all?


YO: As the Chinese saying5 goes: intro, development, pivot, conclusion. Which implies four titles to some people. But that would mean Sonic is the pivot. (laughs) In any case, 3D Space Harrier and 3D Super Hang-on earned us a pretty good reaction, and the people who played it have help spread the word. Thanks to that, this project will continue on a little longer…  Really, though, the next game is coming very soon. (laughs)


5. Kishoutenketsu, a common narrative structure based in Chinese poetry.


NH: Yes, the show goes on for a bit longer. We look forward to everyone’s support!


Thank you very much for your time. Can’t wait to see what you have lined up next! Keep up the good work!



Copyright ©2013 Impress Watch Corporation, an Impress Group company. All rights reserved.

Ishaan Sahdev
Ishaan specializes in game design/sales analysis. He's the former managing editor of Siliconera and wrote the book "The Legend of Zelda - A Complete Development History". He also used to moonlight as a professional manga editor. These days, his day job has nothing to do with games, but the two inform each other nonetheless.