How Duke Nukem II’s parallax scrolling worked

https://lethalguitar.wordpress.com/2022/07/14/how-duke-nukem-iis-parallax-scrolling-worked/

by bpierre • 4 years ago

250 66 4 years ago

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tambourine_man• 4 years ago

IIRC, Karateka did parallax scrolling in Apple II and C64 days.

I've read the technical explanation but it was beyond me at time.

LocalH• 4 years ago

Karateka didn't use any of the C64's advanced features (hardware scrolling, sprites) as far as I know, being a game that originated on the Apple II. It was still very impressive. I wonder which C64 game was the first to have smooth parallax scrolling (at 50/60Hz).

The technique of pre-shifting was used very widely, even on consoles with some form of hardware assistance (Sonic 3 uses pre-shifted images to gain an extra parallax layer in some places, like the Launch Base Zone background, in addition to the two hardware tile layers and single sprite layer, which could be combined in interesting ways via priority bits). Many Amiga games would also dedicate two sprites to generating a parallax layer (as the Agnus chip's "copper" could rewrite sprite registers mid-scanline, two sprites would be sufficient to cover the whole width of the screen via updating the image pointers on the fly, which was really the endgame of the idea of "racing the beam", dedicating a piece of compute logic towards updating registers at extremely high speed)

vidarh• 4 years ago

Karateka is a poor example of Parallax on C64, as it apparently does (slow) bitmap scrolling in front of a static background. Parallax on the C64 tends to rely on the ability to redefine the character set and effectively use it as a tile set. You can smooth scroll characters using the graphics chip, so you only need to move them every 8 pixels.

Combine that with multiple character sets and you get a variation of the Duke Nukem II approach for "free" - you scroll the characters for the background with the foreground, but you flip to a partially scrolled definition of the tiles.

Another approach often used when the background is limited in complexity, is sprites.

A third option is banding. E.g. if the background you want to parallax scroll is above the normal play area, you can use the raster interrupt to control the scrolling independently for each band.

A fourth option is a bitmap scroll of the tile data. This is "easy" if your parallax bands are limited patterns. E.g. you might fill one band of the background with 0123012301230123 over and over, and then just scroll that as a 32 bit pattern in the character definition.

In any case, the key to all of these is that few c64 games use the bitmap mode (a few do), and so you get to offset the slow CPU with moving far less data around. Tack on the hardware sprites and raster interrupt and you can do a lot of interesting stuff.

Here's a great page on Parallax in C64 games with some video:

https://www.c64-wiki.com/wiki/Parallax_Scrolling

antiverse• 4 years ago

Semi-related; a fun bit of juicy drama is always par for HN: "Duke Nukem Stole Graphics from Turrican" - http://www.nemmelheim.de/turrican/news/duke/

bm5k• 4 years ago

A couple of those could be considered "inspired by" if you (a) squint and (b) ignore all the examples that are clearly the same ;)

I played the duke nukem 1 & 2 shareware _back in the day_ but I missed out on Turrican thanks for sending me down this rabbit hole.

gRoberts84• 4 years ago

Fair usage applies :D

daenz• 4 years ago

After watching some gameplay of Turrican[0], which came out in 1990, I'm convinced it is heavily inspired by the NES Contra (1987).

0. https://www.youtube.com/watch?v=P7jP0qQgL-c

toast0• 4 years ago

Turrican being a robot, and the developer being from Germany leads me to believe it may have been inspired by NES Probotector[1] rather than Contra. PS, watching that now I know the struggle of 50hz gamers playing slow games was real... yikes.

[1] https://www.youtube.com/watch?v=WcAjDFvVvaY

alisonatwork• 4 years ago

That's pretty funny. Although, to be honest, I think a lot of the shareware platform games from that era were seen as low budget knock-offs of more famous games on the consoles and 8/16-bit home computers.

aj7• 4 years ago

If the graphic example shows parallax scrolling, I don’t see it. It looks utterly flat to me.

scatters• 4 years ago

The background texture moves relative to the foreground (pipes and walkways). That's all!

chrisseaton3• 4 years ago

Different planes moving at different speeds to simulate them being further away - thee we at what they mean and the example does show it.

rob74• 4 years ago

Ha! You call that parallax scrolling? Then take a look at this (Amiga, 1993): https://www.youtube.com/watch?v=BoiHk_3siYg. In the first level, the bands of clouds are moving in (I think) 6 different levels of parallax, and also the mountain range and swamp below has different levels of parallax. Ok, this was a game that, as one reviewer put it, "squeezes all the graphic power out of the Amiga". Would you believe that this was a computer which was only capable of displaying 32 colors at once? Ok, that was without tricks of course, and this game probably uses every trick in the book...

christkv• 4 years ago

I mean the Duke Nukem 2 parallax is impressive because it's basically beating a square peg into a round hole.

The Amiga had a lot more helpful hardware. Lionheart really is an incredible title for squeezing so much out of the OCS chipset.

ekianjo2• 4 years ago

YOu could also go back to Shadow of the Beast 1, much earlier on the Amiga, with a very impressive feat when it comes to parallax scrollings.

https://www.youtube.com/watch?v=y9BltSvKMlQ

Honestly, PC games were a complete joke compared to whatever was on the Amiga, until Wing Commander 1 came out.

icedchai• 4 years ago

I still remember when I first played Shadow of the Beast, back in 1989 on my Amiga 500. It was incredible.

z3032• 4 years ago

A nice breakdown on how it was done [1]

[1] https://codetapper.com/amiga/sprite-tricks/shadow-of-the-bea...

chrisseaton3• 4 years ago

Ha! You call that parallax scrolling?

Don't get why you need to put down what someone else did because someone else did something better at the same time? Nobody claimed it was the best parallax at the time.

neilwilson• 4 years ago

Perhaps a little context would help

https://genius.com/Monty-python-four-yorkshiremen-live-lyric...

layer82• 4 years ago

I’ll throw in Turrican II level 3-1: https://youtu.be/-TSjfMNAXwU

the_af2• 4 years ago

Cool, and technically impressive!

But this kind of game raises my stress levels :D

Yes, I used to play R-Type, Blood Money, etc. Then I realized I didn't enjoy them, I suffered them.

z3032• 4 years ago

Not to take anything away from the developers but the Amiga does have hardware sprites, hardware scrolling, a blitter, the copper and dual playfield mode to make things a little easier

TacticalCoder• 4 years ago

That vid is a very bad example for the vid itself is not running at 50/60 Hz. And that was the whole thing back then: most great game on the Amiga (and the Atari ST) were running at "full frame rate". Arcade games too (except some still amazing ones like Outrun which was 30 fps IIRC).

A parallax a 50 Hz was silky smooth. A video of a game running at 50 Hz that is recorded at 30 fps doesn't do the original game justice.

The link to Shadow of The Beast (Amiga 1989) is much better in that you can configure YouTube to play the vid at 50 Hz.

vardump2• 4 years ago

While watching 50 Hz content, just need to set monitor to 50 Hz, 100 Hz to eliminate jitter. (Unless you have something like 240 Hz screen.)

mortenjorck• 4 years ago

While not nearly as lush, this is another impressive bit of Amiga parallax scrolling from six years earlier: https://www.youtube.com/watch?v=GwATApeN2Qw

(Also the only video I could find with the original, heroic-sounding music I remember, as everyone else seems to have somehow ended up with a disk image using an oddly-substituted filler track.)

bouncycastle• 4 years ago

Amiga, huh?

The Commodore 64 had smooth parallax scrolling in 1986 without any hardware acceleration. Instead, they used a trick where they rolled the character set definitions, eg. https://www.youtube.com/watch?v=iHrmjP6D1OU

More advanced examples appeared later. eg "Flimbo's Quest" in 1990 https://www.youtube.com/watch?v=SiCxXMquPKs

This video has an explanation for how it worked https://youtu.be/DQpLAIkNVLE?t=165

boomlinde• 4 years ago

I think it's unfair to say that it's "without any hardware acceleration". These tricks work because the VIC-II can unburden the CPU a lot by letting it work with character cells and character definitions instead of individual pixels, and in Parallax, all the CPU needs to do to create the parallax effect is to redefine the 32 bytes that define the background characters.

I didn't know that Flimbo's Quest trick, that's cool!

vardump2• 4 years ago

Not saying that isn't impressive, but there are just two layers of parallax scrolling per horizontal line (= how it's usually counted) in that example.

BTW, many Amiga games could do 3 layers per horizontal line.

StillBored4• 4 years ago

Hmm, maybe my memory is failing me, but VLB went from 0 to 100% on 486 motherboards pretty much overnight. The ISA bus limits (and hence EISA) were well known, and most of the SVGA cards being sold in the early 1990's (like those cirrus logic's) were "accelerated" to compensate for the lack of ISA bandwidth. AKA, they had blit engines, hw cursors, line drawing, etc, and windows drivers to utilize that functionality. I'm fairly certain, although to lazy to dig up the tech manual for them that the blit functionality included alpha channels. Given that 486's themselves were considered high end, I frankly never remember seeing one with an 8 bit EGA card, even 386's usually in the late 80's early 1990's were shipping with 16-bit (S)VGA cards because the 3rd party cards were fairly inexpensive. While EGA lived on in lots of games because it had some convenient modes, actual EGA cards were also fairly short lived in that little window before VGA was released so by the late 1980's weren't being sold with new machines. It was also fairly common to overclock the 8-MHz ISA bus to 10MHz on boards that didn't have VLB. Anyway, my point is that in 1992, low end machines were coming with Hercules graphics and monochrome monitors. Anyone who could afford a color RGB monitor wasn't getting it with VGA/EGA because the monitor was 80% of the price (few hundred dollars) and a 512K SVGA card was well under a hundred.

Anyway, I guess the benchmarks in there were to show how slow plain VGA was, but really by the time frame of duke nukem, 486SX's and VLB were radically changing the PC's performance characteristics, even on fairly low end machines.

PS: I still have the cirrus technical manuals because back in the 1990's you could call up these companies, tell them you were a software developer and they would send you a 400+ page technical manual that details registers and operational/functional characteristics of the boards.

tomxor• 4 years ago

VLB went from 0 to 100% on 486 motherboards pretty much overnight. [...] actual EGA cards were also fairly short lived in that little window before VGA was released so by the late 1980's weren't being sold with new machines

I know the market moved fast back then, but "sales" != "ownership". Sales may have switched to VGA overnight, but if a game wants to maximise it's audience it needs to target what people already own. So unless people buy computers like they buy milk, that would have included EGA cards.

bombcar• 4 years ago

Also upgrades were very very common back then - and you’d often sell back your current card to the store when buying the upgrade. So people would be upgrading to EGA cards as those came back in.

syntheweave• 4 years ago

Also taking place in this time frame was the move towards "multimedia PC" standards. At its onset, MPC Level 1 helped consolidate the standards around VGA spec and Soundblaster audio, when before that, the expectations for PC games were that it was primarily an office computer and didn't "do" graphics or sound, so you just had to try to support everything, especially if you were doing shareware and wanted high install rates. So around 1991, when that spec was released, you start to see VGA as a requirement, but shareware did stay behind the curve to support "granny PCs".

Doom really changed this. Lots of people ran out and got new systems for the sake of Doom, when before there was an association between high end machines and complicated simulator games. And while there were still casual games that remained focused on the "granny PC" well into the 2000's, the market really redefined itself in a big way around this new wave of enthusiasts playing shooter games.

danachow• 4 years ago

included alpha channels

I would be very surprised by this. Raster ops, yes. Alpha channel image compositing operations, no way - that's an entirely whole nother level of complexity.

StillBored4• 4 years ago

Not sure why you are down voted, its a somewhat fair point.

So I looked it up, the 542x series in this article do support "transparency" blt operations, but it might be fair to call them raster ops rather than full blending. They would be be sufficient for the parallax scrolling Duke Nukem here was implementing, which was sorta my original point.

OTOH, full 32-bit ARGB support shows up in the Cirrus line of adapters with the next revision 543x, mostly for video overlay though, although the way its wired seems to leave a lot of open doors for interesting effects too.

And full blown alpha blending shows up one generation later in the 546x series.

So there is full hardware support by the mid 1990's in fairly low end HW/PCs at that point. I've said before on this board that alpha blending was going on all through the 1990's and there are various ways to "cheat" and speed up what is presented in '84 (https://dl.acm.org/doi/10.1145/964965.808606). Pulling my Copy of CGPnP off the shelf it says under compositing "since it is fairly easy to do". I give you a demo from '92 with real time apparent blended transparency: https://www.youtube.com/watch?v=pLJhtefcoPE see about 4 mins in. I sorta doubt this is the first case, but was one I vaguely remembered, since I was myself hacking these kinds of things with my schoolmates around that time as we tried to emulate what we saw others doing/etc. And none of us went into computer graphics or gaming oriented parts of the technology fields.

BTW: That demo notes it needs a 386+VGA, so we are talking late 1980's PC hardware.

touisteur2• 4 years ago

Somewhere in there was MCGA too. I still remember very cool stuff on the 8086 Amstrad PC 1640 that had an EGA card. You had to do palette magic and it was hard to do any animation, but I think games like Xenon 2 and Prince of Persia did a good job of it.

jasomill• 4 years ago

IIRC — I worked in a computer lab full of PS/2 Model 25 at the time — MCGA was just CGA with a couple VGA modes (640x480x2 and 320x200x256) bolted on. In particular, it was not compatible with EGA.

luckyorlame• 4 years ago

Doesn’t it still work that way?

desi_ninja• 4 years ago

great to see lethal guitar's work getting featured here. Rigel Engine is a very cool and ambitious project to revitalize a retro game. He is also very welcoming. I had my fun time contributing to it few years back.

layer82• 4 years ago

TLDR: The primary scrolling used 8-pixel steps (based on 8x8 tiles), while the parallax scrolling was in 4-pixel steps just by using two (or 2x2) variations of the tiles. Also, the EGA hardware allowed copying tiles within video memory with four times the speed of memory accesses from the CPU, by operating EGA latch registers for the four bitplanes in parallel. The number of tiles on the screen where sprites and tiles and background partially overlapped, and therefore required slower drawing methods, was minimized.

dottrap• 4 years ago

Many of the comments here imply this article is about how to do parallax scrolling in general or think the article is suggesting Duke Nukem II was pioneering parallax scrolling. This is not what the article is about.

This article is about how Duke Nukem II specifically implemented drawing so that it could actually achieve playable framerates on EGA video cards and slow ISA buses, which were too slow to do a naive implementation.

ghoomketu• 4 years ago

My god the things programmers had to do back in the day to squeeze every single bit out of the machine and here I was feeling smug using Weakmap instead of map for my code optimisation :P

I also remember carmack's fast square root function. So many amazing tricks. There definitely needs to a site or sub-reddit dedicated to these.

qbasic_forever• 4 years ago

Track down the Graphics Gems series of books, it's what most of the game devs back in that era used to get tricks like fast square root, etc. https://www.realtimerendering.com/resources/GraphicsGems/

sumtechguy• 4 years ago

I always liked this site for some interesting tricks.

https://graphics.stanford.edu/~seander/bithacks.html

gwbas1c• 4 years ago

Earlier, I also said that VGA games more frequently featured parallax, and that VGA was easier to program than EGA. This is primarily because in 256-color VGA mode, each pixel always occupies one byte. So all the complexity caused by the need to address individual bits disappears. VGA still has a planar memory layout, but this applies to bytes instead of bits.

My dad picked up an old EGA computer from work in the early 90s. I was always frustrated that almost all games required a VGA at the time. Now I understand why... It was too much effort to be backwards compatible with what was increasingly becoming niche hardware.

tdumitrescu• 4 years ago

It wasn't just coding, it was also a lot of design/art resources. Going from 256->16 colors would look terrible with automatic dithering. My recollection is that there were a few Sierra titles made for VGA that also supported EGA and that it looked like someone had gone through each screen by hand to make the low-color ones look acceptable-ish.

the_af2• 4 years ago

EGA art specifically designed for EGA could look beautiful. For example, I love EGA Monkey Island. Most adventures with EGA support had different graphics for EGA vs VGA.

But yeah, automatic dithering didn't look nice.

Andrew_nenakhov2• 4 years ago

Interestingly, original "Loom" by Lucasfilm looks much better in EGA [1] than its later VGA edition does.

[1] http://www.superrune.com/tutorials/loom_ega.php

treve• 4 years ago

I feel a limited palette can push creativity. Not only when it's literally about color palettes.

minikomi• 4 years ago

A note to mobile users: you can tap the EGA images to see the VGA versions

davedx• 4 years ago

I remember implementing a side scrolling platformer on my 386 and being boggled by how slow everything was compared to on consoles. Didn’t know what hardware acceleration was then, and this was before I got Internet access so I worked it out myself, coded it in C, then hand optimized the inner drawing loop in assembly, rewriting the pixel writes to use rep/mov instructions for each tile. This took a while but I managed to squeeze out acceptable performance for my game with Keen-like smooth scrolling.

Reading Masters of Doom some 30 years later was pretty eye opening. This article too - to this day I’ve never heard of latch writes.

So much voodoo in graphics programming!!

moosedev• 4 years ago

Since you mentioned latch writes, check out Michael Abrash’s Graphics Programming Black Book[0], chapter 23 onwards, if you feel like immersing yourself further in well-written VGA lore.

Not recommended for your present-day productivity (unless you’re making retro games!)

[0] https://www.jagregory.com/abrash-black-book/

dylan604• 4 years ago

Maybe that's where the 3dfx voodoo name originates?

Dwedit• 4 years ago

I never would have guessed that this game was using an EGA mode. Using a non-default palette completely fooled me.

How Duke Nukem II’s parallax scrolling worked

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