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Comment by jblow | Hacker News Reader

Wrong, wrong, wrong, wrong. Wrong.

People in the video game industry wrote tons of this stuff. We would spend weeks figuring out how to get one or two instructions out of the rasterizer or scanline converter, etc. I know this because I was there. I wrote several software rasterizers, and I learned how to do it by reading papers and magazine articles written by other people who wrote software rasterizers.

I have no doubt that other industries did so as well.

Even more recently, companies like RAD Game Tools built as products software rasterizers that are very fast (e.g. Pixomatic).

Also, what's in this article is a simplified introductory take. It is actually much much more complicated than this. (It doesn't look to me like he is doing perspective-correct shading, for example.) Also this guy's code is crazy slow compared to what you'd write in the real world, but hey, it is a tutorial.

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> Also this guy's code is crazy slow compared to what you'd write in the real world, but hey, it is a tutorial.

I read pandaman's comment to mean this, actually. Not that nobody wrote their own handcrafted rasterizer/poly engine whatnots.

It's that the article is both not showing what GPU's do internally, but it also doesn't quite show what a reasonable "artisanal" poly rasterizer gfx engine would look like for a system with no GPU. On the one hand, sure, it's a tutorial, so it just shows an overview of the steps a proper engine would need to complete, but it's done with an almost pseudocode-level of inefficiency. Sadly (just a little), it'll run fast enough on a modern computer that I am sure that some people will just take this example and use it as the core of an engine to build something crazy cool around :) And frankly, more power to them. Analogously if someone had told me 17 years ago that Javascript would one day associated with the term "web assembly", that it would be used as a low-level target for compilers, and for many purposes the first choice in application (even graphical) development ... I never expected the future to be anything less than weirder than I could possibly imagine, so let's just write code! hahaha :-)

(actually edited that from 15 to 17 years ago, because I remember in 2002 there were already some possible inklings of hints of what could be done in JS, XHR was on the glimpse of becoming mainstream accessible, the possibilities were all but not quite crystallised)

Are you sure? You have shipped games with software rasterizers and they did this exact algo (no matrices in transform, computing gradient for each scanline)?

I also wrote software renderers in the 90s. I would say it was mixed. Some people used matrices, and some didn't. You really can't say that everybody used the matrix formalism across the board. For that matter, I worked on an engine at a well-known game company as recently as 2013, where there were definitely hand-optimized paths for several different cases of transforms where the constraints were known. Generally speaking, game programmers will do whatever it takes, and painstakingly optimizing algos down to minimum arithmetic operations has always been pretty common in the field.

I too wrote software rasterizers in 90s and even shipped a game with one. If you used a single sine for each vertix, least computing full rotation, you were fucked. There was no hardware, which could handle this at real time in 90s.

If you did division for each scanline, you were running at 1/4th of the speed at most - division was that expensive on 386-Pentium, not to mention other platforms, where CPU's could not even have hardware div.

> Generally speaking, game programmers will do whatever it takes, and painstakingly optimizing algos down to minimum processor operations has always been pretty common in the field.

I am not even talking about crazy optimizations (like using intel's x86 half register to do ghetto fixed point), I am talking about common sense stuff.

Ah. I think you're talking about something completely different from what jblow and I were talking about. If you mean that the code in the article is not optimized, and is doing crippling amounts of redundant computation, then of course I agree with you.

The guy asked what kind of magic is calling trig functions in inner loops? I replied that nobody really did it and I am confused as to what the author was trying to show.

I, frankly, do not understand what you and jblow read into this other than what I said.

Hahaha, I guess it's a big misunderstanding. You wrote:

"Nobody really wrote software rendering like that beyond CG classes".

I read this as a claim that nobody in general wrote software renderers. When by "like that" you just meant using the specific techniques he used.

That said, I still have to disagree, in the sense that, to get to a fast software renderer, you start with a slow software renderer. Nobody does all the crazy optimizations a priori ... so stuff like a divide per pixel was common, say. Calling trig functions in inner loops is of course goofy, but my presumption is that in the next step of refinement those would be lifted out of the loops, because that is the way things are always done.

As I said, it's bad as a tutorial:

It enforces the stupid idea, that you rasterize 2D triangles for a 3D renderer. People, who think this way are then completely shocked and mystified as to why there is perspective distortion to the surface attributes.

And then, on 2D triangles, it enforces a bizarre notion that a triangle is not flat, so the surface attributes gradients can change from scanline to scanline.

> Nobody does all the crazy optimizations a priori ... so stuff like a divide per pixel was common, say. Calling trig functions in inner loops is of course goofy, but my presumption is that in the next step of refinement those would be lifted out of the loops, because that is the way things are always done.

Yeah, .. but no. Depends on what era you're talking about I guess.

When I wrote my first low-level rasterizer + basic 3D poly engine-ish-thing in 1998, I honestly wouldn't have considered for a second to do a division per scanline. An integer add was one tick, a mul was 3-10 (iirc), but a division was 10-40 ticks. Depending on what point you start considering the optimizatons "crazy", yes, had I known (and cared) about perspective correct shading back then, I would have started designing the algorithm, a priori (which for me usually meant on grid-paper) hunting for some way of faking a sufficiently accurate reciprocal using adds, shifts and at most 2 muls (per scanline, cause per pixel even a single mul was madness, obviously). With what I knew back then, probably go for a 2nd degree polynomial that might be sufficient to at least give the impression it was doing better than naive bilinear? :) Had I been aware of Carmack's (objectively crazy) inverse sqrt hack, I would probably have started looking in that direction (abusing the IEEE float spec on the bit level woohooooo).

Sure you could write a perspective correct triangle rasteriser with a div per scanline, and it would be too slow, it would be a nice theoretical proof of concept, but it would also be kinda useless if it turned out you couldn't make the above crazy hacks run fast enough. They were a real hurdle that had to be crossed or you might as well not bother. Also, why save the fun stuff for last? ;-)

> like using intel's x86 half register to do ghetto fixed point

Just curious, what's this and how does it work?

x86 has a bizarre register architecture. 4 "general purpose" registers are like this : EAX & 0xffff == AX == (AH<<8) | AL i.e. the lower 16 bit portion of a 32bit register is a separate 16bit register, which, in turn, is made of two 8bit registers. If you stored a 8.8 value in a AX, for example, you could immediately access the integer part through AH. Of course, 8.8 numbers are not good for all values but you could write fast texturing loops with them (256x256 used to be a solid size for a texture so 8.8 was okay for texcoords).

whoa, my compliments how you managed to explain in a single paragraph both the bizarre x86 registers and fixed point math, succinctly :)

Look up tables for pre-computed sine values. Search for "Denthor's tutorials" from the Asphyxia Demo group.

Q: "Did you ship a game doing this?" A: "Lookup tables!"

If you were smart enough to use lookup tables, you were already too smart to transform each vertex in multiple steps instead of folding all transforms into a single matrix.

Yup - it happened - I remember several games that just used trig. via lookup tables. (Esp. If they were mostly Z only rotation - cf. battlezone). Also, many games rasterized convex polygons, so gradient per scanline was a thing.

In those days there was so little information easily available - and very little contact with other coders. Once you had figured out something that kinda worked, you got on with making a game.

The European demo scene did a lot to move ideas around, but was not quite the same as game development.

Demos are not production games, it's kids teaching themselves. I should have written "beyond CG classes and demoscene".

That's one way of putting it. In the early 2000s, commercial production games were just as much "demos done inefficiently" (for good business reasons, mostly). Maybe I sense an unintended connotation with the term "kids", though.

I remember ATI came to demonstrate their GPU at the Breakpoint demoparties (02/03 or so?) .. it was not unimpressive, and I didn't really understand what a "shader" was in the context of a GPU back then (it was also a dumb choice for a name, given what "shading" meant in gfx programming back then, the term "vertex shader" was borderline nonsensical). But they mainly showed stuff we could already do, except doing it in a higher resolution (on what had to have been the most high-end consumer hardware available, ATI brought themselves, it wasn't the official compo machine, for sure). Given I now know what a GPU shader does (parallelism, domain specific instructions but mainly parallelism), I know that "the same thing but on a higher resolution", is absolutely the most obvious thing you can do with a GPU over just a CPU. In demoscene terms, boooooring :-P

This was a few years later, THIS is what a demoscener does to a GPU: https://directtovideo.wordpress.com/2009/10/06/a-thoroughly-...

Either way, at some point (late 200X's?) professional game industry blew past the demoscene in production level. It did happen. I always thought it was the Hollywood movie level budgets (because those exploded too, in that era, didn't they?), but there might have been other factors.

My memory of early 2000s is different. Commercial games gave up on software rendering with PS2, ubiquitous 3D cards on PC and Microsoft paying everyone who agreed to develop for the Xbox. Graphics programming in games then was not much different than now. It was about giving good tools to artists and designers and not about doing "cool fx". Though I cannot speak for the whole industry, obviously, just what I've experienced.

> it was also a dumb choice for a name

Blame Steve Jobs and his Renderman :) At the time consumer GPUs with shaders came out it's been long established term for any code processing graphics data during rendering.

>Either way, at some point (late 200X's?) professional game industry blew past the demoscene in production level. It did happen. I always thought it was the Hollywood movie level budgets (because those exploded too, in that era, didn't they?), but there might have been other factors.

I remember in mid 90s some demo-groups claimed to work on actual games ("Into the shadows" guys said it's a prototype for the game they had been writing) and even on hardware (Pyramid3D lol) but I don't think anything noticeable came out. Remedy Entertainment is, probably, the most successful exit from the demoscene and it never set the bar for the AAA industry. The difference between demos and games is the difference between dancing and fighting. You move your body in both cases but with dancing you are fine as long as you pull some cool moves, while in fighting you actually need to survive and harm your opponent as much as possible. Same as in games you need to draw what the artists want and in demos you can draw anything as long as it's cool. There was never a sensible competition between the two. I imagine game programmers suck at making demos just as much as democoders suck at making games :)

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