Rendering my (billiard) balls in a fragment shader

Rendering my (billiard) balls in a fragment shader(getlazarus.org)

244 points by sysrpl 3 years ago | 84 comments

sysrpl 3 years ago |

Here is a summary I wrote on my attempt to render balls using only a fragment shader. I am pretty happy with the result, and I've included a breakdown of the creation process.

radarsat1 3 years ago | |

Great write up, that was a fun read.

In understanding how the rotation was implemented, it took me longer than it probably should have to realize that the normal map (which I think of in terms of lighting) is actually a radial position on the sphere.

I had to go back and forth with the final and original code a few times, and finally noted that "n" gets renamed to "point" when it becomes an argument to colorLookup.

This dual usage of the normal for lighting brightness calculation and as a radial position on the sphere surface for looking up the color makes sense in retrospect but is also a somewhat subtle aspect that you might want to address more explicitly in your text instead of just silently renaming the variable in the code.

Zinu 3 years ago | |

In the final video, there are still some texture artifacts whenever the number is on the edge (e.g. the ball 4 at 5 seconds). Maybe because of mipmaps? I can't really think of a reason why it happens. It even happens at the bottom of the 4, even though that part is white in the texture.

Jasper_ 3 years ago | |

Nice work! My only recommendation is to add a pow(color, 1.0/2.2) or similar at the end, and then turn down your light brightness. Your light falloff has the distinctive look of gamma-space lighting makes it look dated and less realistic. Doing your lighting in linear space should help.

It might also be simpler to do your rotations without a matrix, for the learners ( just expand out the functions, e.g. https://github.com/magcius/sw3dv/blob/gh-pages/b_vert.glsl#L... )

marklubi 3 years ago | |

Great article! I would be interested in more info about the physics and ball path mapping that you mentioned in the beginning.

Over the last few months, I’ve started competing in billiards, and the roll vs slide, english, tangent lines, and even forced follow to be incredibly interesting.

Is any of that involved in the physics simulations that you’ve worked out? If it is, I would really like to know more.

prox 3 years ago | |

Cool, I recently started with GLSL, and it’s interesting there are many roads that lead to a similar solution (how I draw circles or make a center is tad different)

Where or how did you learn GLSL?

sysrpl 3 years ago | | |

I was around and writing OpenGL when we started getting the first programmable cards. Nvidia shot out first with their Cg language, but I held back and waited for the "Orange Book" to come up. I bought it right away and learned from it and by looking at other peoples shaders.

https://duckduckgo.com/?q=opengl+orange+book

Also the quick reference card helps

https://duckduckgo.com/?q=glsl+quick+reference&t=h_&ia=web

the__alchemist 3 years ago |

Good timing - I was procrastinating on HN instead of trying to fix my phucked-up phong; you've helped me do both.

sysrpl 3 years ago | |

With a good phong it's all about the dot products and specular highlight (if you using highlights). Make sure you clamp the dot products and give yourself a minimum ambient light value of around 0.15 to 0.2.

Jasper_ 3 years ago | |

The thing that got me, in a classic Phong, you have to test whether dot > 0.0, it really won't work outside of the front hemiphere. The clamp isn't enough.

pixel_tracing 3 years ago |

Came for the title, stayed for the shaders. Well written and very educational

eyelidlessness 3 years ago | |

> Came for the title

Well played

Edit: I’ll take the downvotes, the author edited the thing for silly innuendo, it’s silly, I’ll have fun too and take my lashes.

virtualritz 3 years ago |

In the 90's, texture maps were a luxury for anything. As a result shaders (for offline rendering, realtime shading languages didn't exist yet) were doing everything procedurally.

Here is the only image I could find of the RenderMan Shading Language VIDI SPORTS SHADERS Makina Works sold at the time (you got no source, just bytecode understood by Pixar's implementation at the time, AFAIK):

https://web.cs.wpi.edu/~matt/courses/cs563/talks/renderman/S...

What is interesting here is that the shaders did everything on a sphere primitive. All RenderMan implementations at the time (there were more than just Pixar's) were micropolygon renderers. I.e. displacement was almost free in terms of compute overhead.

Even the football operated on a sphere that the shader deformed into the resp. shape. All patterns, stripes etc. were procedurally generated. Each shader had texture slots to apply custom logos.

halaiis 3 years ago |

This reminds me of the same rendering technique described in Hustle Kings for the PS3. There was a write up done, however shader code was not included.

https://web.archive.org/web/20130913033312/http://www.voofoo...

sysrpl 3 years ago | |

That's very interesting. Thank you for the link. From what I read and see in the images, I gather he's done the same thing I have, as you guessed as well. Obviously he's going much further. The author is using a subtle bump map (simulating balls scratches and imperfections), a reflection map with a gradient and indecent angle, what looks to be a faux sub surface scattering effect.

Also he is placing his balls in a 3D environment with nice shadows that really help to sell the illusion.

That's a good find and an interesting read. Thank you.

samlittlewood 3 years ago |

It might be interesting to explore with the students why this would not be quite right for a general 3D view, and how it could be fixed. Conic sections, etc.

MaxBorsch228 3 years ago |

I guessed correctly by the title that the article is about coding a 3d image, but was waiting for the classic "two balls and a cylinder" scene, which college students naturally come up with in path tracing assignment in computer graphics courses.

spuz 3 years ago |

I'm just getting my feet wet with shaders myself. Could this fragment shader be used in a "real" 3D game? At the moment, the sphere is orthographicly projected onto the screen so the sphere will always appear as a circle rather than an ellipse. How easy would it be to use this shader in place of a spherical mesh as you might find in a typical geometry based 3D render? I.e. could you use the same technique and render multiple balls on the screen with positions in 3D space and rendered correctly taking into account any distortion caused by the camera?

londons_explore 3 years ago |

What's the benefit of rendering using this technique over a regular sphere rendered with the usual pipeline?

sysrpl 3 years ago | |

Well first of you get infinite smoothness and better lighting (and reflections if you add them) because there is no underlying geometry. It's just math. It's also much faster, as you're only giving the GPU four vertices defining the square. This can even be sped up further by using point sprites which consume only one vertex.

gsliepen 3 years ago | | |

"It's just math." But math can be expensive, and in the fragment shader you are calculating everything per-pixel, whereas if you provide your geometry to the vertex shader, you only have to calculate something once per vertex, which is usually much less.

Furthermore, depending on the GPU and the exact workload, it can be that vertex and fragment shading can run in parallel. In that case, it is better to spread the load over both, instead of letting the fragment shaders do everything.

The same goes for texturing. Instead of calculating most of the ball's color pattern in the fragment shader, and only using texture lookups for the number itself, if you just have a texture covering the whole ball, you basically offload a lot of computation to the texture units.

That said, for a pool game where the balls are one of the most important items on the screen, it's probably worth it to get the perfect smoothness and lighting, as you mentioned.

cowtools 3 years ago | | |

I've been advised not to use point sprites. Apparently, most GPU inplementations merely convert it into a quad in the backend, and gl_PointSize seems to have a soft maximum that depends on implementation.

I've found a mechanism that uses the "interleaved attribs" feature of transform feedbacks to spit out 4 verts at a time (as six to draw two GL_TRIANGLES) into a buffer that a quad-drawing shader program consumes.

Using GL_POINTS/gl_PointCoord is probably better though just for teaching children fundamentals, I just wish that it actually worked properly in practice.

cowtools 3 years ago | |

It is faster for the case of a "top-down" 2D game. You render this and just draw a single quad per ball. You do not really have any vert shader.

ricardobayes 3 years ago |

Even after 10 years I still have anxiety looking at OpenGL code. I still don't understand why we needed to write ray-tracing during a BSc course starting from a blinking cursor. The professor tried to defend that at the time, but I firmly believe that it is the wrong curriculum for a 20 year old CS student. Computer graphics were and are niche programming, and should not be taught main-stream. Out of 100 graduates maybe one will ever use this, why not use some common sense and teach something useful?

skywal_l 3 years ago | |

Because graphics is fun. It's a good way to engage with students. Beside, what's important is not the outcome but the journey. You learn to read documentation, to design, to debug and more importantly you learn to learn. Which is what higher education is about.

npteljes 3 years ago | |

Education is about exercising the mind. I don't think many play with inflated balls in their adulthood, yet it's very important to teach children hand-eye coordination, team play, and other concepts so that they become better functioning humans.

There are problems with the curriculum though, one of them that it plays catch-up with the state of the world. IT in particular moves very fast. Graphics programming is not one of these things however. For example, if you've done the courses, and experiences just how hard it is to crate anything in 3d, you can better appreciate the work that goes into modern 3d engines. Look at this beautiful breakdown of the inner workings of the GTA V engine:

http://www.adriancourreges.com/blog/2015/11/02/gta-v-graphic...

NavinF 3 years ago | |

inb4 you get 10 replies along the lines of "wow I wish my professors let me do something cool like ray-tracing. I spent 4 years implementing cache-inefficient data structures that nobody uses in an ancient version of some programming language that nobody uses in a crappy env doesn't even have a real debugger"

Not that I can relate. I dropped out of uni well before I encountered anything that would discourage me from going into software :)

pfoof 3 years ago |

Cool to read about C-like GLSL on a Pascal website

pjmlp 3 years ago | |

In theory if Free Pascal had a SPIR-V backend, it could be used as well.

gitgud 3 years ago |

Very nice! not sure if you've heard of [1] ShaderToy, but it's pretty good for sharing/viewing shaders online.

[1] https://www.shadertoy.com/

gfody 3 years ago | |

https://www.shadertoy.com/view/XlfBRH https://www.shadertoy.com/view/MtlGD8

pupppet 3 years ago |

Pretty interesting how he's wrapping the text before the curved image on the right.

drzel 3 years ago |

not sure about that red 10-ball tho.

xanthine 3 years ago |

I happened to notice that PI is #define'd to 3.1415926538, which isn't the correctly rounded off value of 3.14159265358...

Seems like they missed a '5'.

causality0 3 years ago |

From the HN guidelines: please use the original title, unless it is misleading or linkbait; don't editorialize.

The correct title is Rendering Pool Balls, not "Rendering my balls in a fragment shader".

sysrpl 3 years ago | |

Fixed.

dang 3 years ago | | |

Not to pee on your party, but I wouldn't want to the users who click on that title expecting...something else, to be disappointed. Therefore I have made the minimum viable edit.

(For anyone wondering: the submitted title was "Rendering my balls in a fragment shader" and the article title was changed from "Rendering pool balls" to that.)

TaylorAlexander 3 years ago | | |

I love how you fixed it lmao.

jahewson 3 years ago | | |

Outrageous! Well done.

ketzo 3 years ago | | |

…well played

echelon 3 years ago | | |

Malicious compliance. Love it.

I'll be referencing this in the future.

password4321 3 years ago | | |

A new HN meme is born.

quickthrower2 3 years ago | | |

Based!

chris_wot 3 years ago | |

Well that backfired on you.

rawoke083600 3 years ago | |

boo !

can16358p 3 years ago |

Could we change the title to the actual title of the article?

I was, let's say, really scared when tapping the link with the current title.

sysrpl 3 years ago | |

I fixed it. Thanks.

javawizard 3 years ago | | |

What was it originally? Hard to get more amusing than the actual article title...

NavinF 3 years ago | | |

Well played

noam_compsci 3 years ago |

Risky click of the day

benj111 3 years ago |

Fyi.

"Rendering my balls" says something very different to "rendering balls".

Although the hair would be impressive if you managed to do it.

(Testicles btw)

silverfox17 3 years ago | |

I believe they titled it that way on purpose.

hermitcrab 3 years ago | |

(Testes btw)

benj111 3 years ago | | |

I like how you can confidently correct me over the hyper precise term 'balls'.

Even though the term 'balls' generally includes the sack (and hair) which neither of us accounted for.

acqbu 3 years ago |

To me, those balls are perfect

rawoke083600 3 years ago |

The sexes(including all modern derivatives) may really be equal, but I for one truley enjoyed this title submitted most likely by a male :p