Top dweets by u/tomxor

function u(t) {

c.width=1920 // clear the canvas
for(i=0;i<9;i++)
x.fillRect(400+i*100+S(t)*300,400,50,200) // draw 50x200 rects

} // 122/140

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    u(t) is called 60 times per second.
    t: Elapsed time in seconds.
    S: Shorthand for Math.sin.
    C: Shorthand for Math.cos.
    T: Shorthand for Math.tan.
    R: Function that generates rgba-strings, usage ex.: R(255, 255, 255, 0.5)
    c: A 1920x1080 canvas.
    x: A 2D context for that canvas.

Try the new frontend: beta.dwitter.net
Current theme challenge: #Opposites

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tomxor

remix of d/15534 by u/tomxor

function u(t) {

Z=_=>C(3*S(Y+C(X*3))+3*S(X+S(Y*3))+t*4)**3/6
for(c.width=i=1024;i-=1/16;x.fillRect(48*(X*2+Y+11),48*(X/2-Y+z),1,5))z=6-Z(X=i%8-4,Y=i/128-4)

Aug 28 2019 11:57 AM UTC

}// 139/140

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#lava

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tomxor

function u(t) {

eval(unescape(escape`𩡯𬠨𨰮𭱩𩁴𪀦👙👚👩🐷𩐴𞱩𞱓𚰽𦀬𠰫👙𛁔𚰽𦠩𚀱𚱓𛰲𜑞𠰯𜐸𧡔𛰱𝠩𙐱𝑼𯀨𦀽𦐬𦐽𦠬𬠽𭑛𪰽𦱾𤰬啓𛁾𥁝𧑼👚👓𚡴𙐲𛐱𛀭𛑩🠴𩐴🱩𙐶🱵𦱫𧐫𚰺𤰽𠰽𥀽𜐸𝀺𮀮𩡩𫁬𤡥𨱴𚁘👩𙠲𝐵𛁙👩🠾𞀬𞀯𚀸𚱲𛱴𚐬𦠽𜐬𤰽𠰽𥀽𜐲𞀬𦀽𦀯𤰭𜐬𦐯👓𚐩`.replace(/u../g,'')))

Dec 9 2024 12:16 PM UTC

}// 140/140

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Photon-Mapping using a Random-March Scattering Model

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u/tomxor

A (very inefficient) physically based renderer in a Dweet! :) Give it 5 mins for reasonable convergence, the longer the better, Firefox is fastest. I know this is not the most interesting visually, but I found it challenging to make, and didn't fully understand the result. So the following hand wavey write-up is more of an analysis as I attempt to understand what's going on. I am not a PBR expert so I probably don't know what I'm talking about.
u/tomxor

This approach conceptually follows Photon Mapping, where light rays are forward traced, bouncing around the scene recursively, accumulating radiance into a spatial map on each bounce. Essentially painting reachable surfaces with light. Separately a ray for each pixel is cast into the scene to retrieve the current radiance for the position it intersects. From here, implementation deviates substantially from the original algorithm. Rays are marched. The map only stores irradiance, and uses spatial hashing instead of a kd-tree. However the most interesting differences are in surface interactions. BSDFs are the standard abstractions for reflectance and transmission but they are far too large to implement. Through "experimentation", AKA messing around on Dwitter, I found a roughly Lambertian reflectance distribution to emerge from a simple random march. Lambertian meaning a perfectly diffuse surface, which causes uniform propagation through 3D space, but a necessarily non-uniform distribution of reflected angles (this is worth taking some time to understand separately if it's not immediately intuitive).
u/tomxor

With ray marching each intersection naturally ends up embedded in a surface. Instead of correcting this, a new direction is randomly chosen and the ray is sent on it's way. Depending on the surface intersection depth and angle of reflection there is a chance the ray will escape (reflect) or remain trapped (absorbed). With the chance being greatest when reflecting in line with the surface normal, and lowest when parallel to the surface. Note how the surface, depth, and reflection ray form a right-triangle. For the reflection ray to escape, the depth must be less than cos(θ) at a step size of 1. Therefore assuming a uniformly random depth between 0 and 1, the reflectance distribution follows Lambert's cosine law. Additionally unlike a BSDF this provides random absorption for free, but with the disadvantage of reflectance distribution and absorption rate being inextricably linked. Another significant difference is that BSDFs are a statistical abstraction designed to extract the most value from each ray by modulating its radiance, representing many photons; whereas this model effectively represents a single photon for each surface intersection. Absorbed rays are thrown away rather than modulated, and each irradiance accumulation is an integer increment. The implication being the random march requires far more rays to converge because each ray has a binary existence and intensity like a photon, on the other hand each intersection is far simpler computationally compared to BSDFs.
u/tomxor

There are a few more gnarly details that complicate this. For simplicity I suggested trapped rays are immediately absorbed, which is possible, but it's simpler to allow them to rattle around a bit. This "widens" the reflectance distribution and increases overall reflectance, to a degree depending on how many consecutive intersections are allowed. But it also changes the overall behaviour by producing a slight Subsurface Scattering effect like skin or paper. Surfaces soften and glow as rays traverse, and weak points like corners diffuse as some rays tunnel through. Secondly, rays with a higher angle of incidence (ωi) have a lower max surface depth, yet the reflectance step length is unaffected. This difference distorts the reflectance distribution as ωi increases. When (ωr < ωi) escape is certain, and when (ωr > ωi) the chance abruptly returns to cos(ωr)/cos(ωi). i.e min(1, cos(ωr)/cos(ωi)). At ωi=0 the distribution is perfectly Lambertian, and at ωi=π/2 it is unnaturally uniform in angle. AFAIK this is not a physically realistic reaction to ωi. It almost resembles Fresnel reflections, where transmissive surfaces reflect more at grazing angles. However Fresnel is anisotropic, like a mirror. Yet here the distribution is centered around the surface normal. This is still a simplified analysis, it ignores subsurface marching, and how adjacent ωr and ωi share pseudo random variables (see below). The chaotic nature and compounding biases means an accurate distribution can probably only be obtained empirically.
u/tomxor

Finally, the ray step/direction vector, must be randomised upon each intersection. Initialising random unit vectors takes a lot of code, so there's a few tricks going on here, but these tricks also affect the result and noticeably compromise accuracy. Rather than a unit vector I've settled for a point in a cube, where the length is anywhere between 0 and 1. This actually helps convergence by randomising depth at repeat surface intersections, however the cube shape results in non-uniform propagation so distance based shading of all the axis aligned surfaces looks a bit too flat. Doing this three times still takes a lot of code, so only Z is randomized upon each intersection, and is then reused by cycling through the XY components, which provides a pretty bad but not-terrible distribution, apparently making it harder to reflect into corners. Z's randomisation combines t with one component of the ray position, so it is effectively a kind of feedback PRNG derived from the very scene geometry the randomness is being used to traverse, which I find kind of neat.
u/Joachim

Insane! Looks sooo realistic :0
u/fentbiggesthater

wow just came back from my vacation in saudi arabia. im now back in my 10m penthouse in new york and this is the first post ive seen after coming back that has genuinely impressed me. good job!
u/UEZ

Very impressive - well done! How can I understand: k = [~S, ~C, ~v], u[k] |= Z. Array u refers to what? Associative arra? Thx.
u/tomxor

Thanks. u is the dweet function which I'm exploiting as a predefined object for the spatial map. The purpose of bitwise inverting ~ each component is to obtain a floored version of the ray position (that it happens to invert doesn't matter) e.g [~0.1,~1.2,~2.3] = [-1,-2,-3], and importantly all positions between [0,1,2] and [1,2,3] will result in [-1,-2,-3] i.e it is binning positions into an integer grid. When passed as a key to u this is coerced into a string to become '-1,-2,-3'. The idea is to count photon intersections into each grid cell with u[k]++ as a kind of frequency based irradiance, but as an object each cell must be initialised before incrementing, so u[k]|=Z uses bitwise again to coerce all values into an int, ORing with Z will convert undefined values to 0, and existing integer values will be unaffected because Z is always less than 1.
u/UEZ

Thanks tomxor. The math / physics behind is too high for me ^^. My question is more related to understand JS what u[k] is. k is an array which is passed to u. When k=[10, 20, 30], what is the result in u[k]++?
u/magna

u/UEZ The property accessor [key] coerces key to a string. So, when you do obj[a] and a is [1,2] it will be obj['1,2'] because [1,2].toString() implicitly called.
u/magna

u/tomxor Another epic one!
u/UEZ

Thx magna :-) More or less what tomxor wrote. Just for my understand, does u[k]++ mean, when k=[1,2,3], u is u['2,3,4']?
u/fentbiggesthater

hm coll
u/tomxor

I think you're getting hung up on the array like key notation, but it's not being used as an array. Think of -1,-2,-3 as an abitrary property name on an object, the u.-1,-2,-3 property syntax would be equivalent if not for the invalid chars. u[k]++ simply increments a number stored for the property k, ++ only works because that property value has been previously initialised using u[k]|=0 which will convert undefined values to 0.
u/jellyedwards

Holy crap! They need to add a dwitter category to the Nobel awards for stuff like this!
u/0x61

[insert image of dribbling cat] We're not worthy. This is endgame
u/KilledByAPixel

https://www.reddit.com/r/tinycode/comments/1…

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tomxor

remix of d/27932 by u/tomxor

function u(t) {

eval(unescape(escape`𩡯𬠨𭀿𭰽𨰮𭱩𩁴𪀦👩🐱𜀳𝠸𞡭👯𫡭𫱵𬱥𫑯𭡥👥🐾𫐽𩐻𦀽𛐭𪐥𭰬𦐽𪐯𭰻𮀮𩡩𫁬𤡥𨱴𚁘𚱺𚡒𛁙𚱺𚡔𛁓👍𨑴𪀮𪁹𬁯𭀨𤠽𦀯𝠴𛑭𛡸𛰲𞀰𯁼𜀬𥀽𦐯𝠴𛑭𛡹𛰲𞀰𯁼𜐩𚰡𮠯𜠬𜐩𚑺🐨𭰫𦀯𜰭𦐯𜱞𦐯𜰫𦀯𜰩𙐲𜐾𜐸𛁺𚰽𭑛𪑝𯀽𫐮𨡵𭁴𫱮𬰯𤰯𝀸𙠲`.replace(/u../g,'')))

Jun 8 2023 2:59 PM UTC

}// 140/140

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#interactive (mouse + drag) #soldering #simulator

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u/tomxor

Here ya go u/joeytwiddle :D don't make a mess! no room for solder wick.
u/tomxor

I'm not sure who tapes a flashlight to their soldering iron though... maybe Doom guy does, ya know, just incase zombies, while soldering door control panels on Mars.
u/danny@hille.dk

Super impressive!
u/Joachim

THIS IS SO COOL
u/tomxor

Thanks guys :) I'm happy with the realism on this one, looks just like my crappy soldering :P
u/magna

OMG
u/joeytwiddle

haha awesome!

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tomxor

remix of d/15559 by u/tomxor

function u(t) {

eval(unescape(escape`𩡯𬠨𩠽𪰽🡃𚀵𚡓𚀨𦠽𜡥𝀯𬀯𪰩𛰳𚱃𚁘👚𚠨𬀯𝠴𙐲𛐱𚐫𭀯𪰩𚐫𝐪𤰨𦀯𜰫𤰨𦠩𚐩𚠪𜰬𨰮𭱩𩁴𪀽𬀽𭰽𜐲𞀻𚰫𬀼𜡥𝀻𮀮𩡩𫁬𤡥𨱴𚁰𙑷𛁰𛱷𛀱𛀨𞐪𠐭𥀩𚡰𛰴𩐳𛐹𚐩𠐽𩠨𛠳𚐬𠠽𩠨𜰩𛁸𛡦𪑬𫁓𭁹𫁥👒𚁔🀱🱁𚡷𚰲𝐶𞡔𛁔𛁔🐹𚡁𚰹𚡂𚰹𚱁𚡂𚐻`.replace(/u../g,'')))

Sep 13 2022 1:47 AM UTC

}// 140/140

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#Lava Fields

u/tomxor

Perspective map all teh things!!1
u/jdspugh

Super
u/Joachim

:O
u/danny@hille.dk

Man this is cool! I want to remix :-)

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tomxor

remix of d/23968 by u/KilledByAPixel

function u(t) {

for(X=t?X+r*50:0,i=h=11+6*C(t*4+X%1)<<5;--i;x.fillRect(...t?[X-r*i/4,600+(r*8&3?i-h:h-i),i/4,2]:[i*8,r*999,h,r]))r=Math.random()

Oct 2 2021 12:56 PM UTC

}// 128/140

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Smolr Tree Lake

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u/tomxor

A nice round 2**7 chars. A bit of bitwise, ternary trimming and coefficient concessions
u/KilledByAPixel

nice! I'm surprised you didn't get rid of the Math.random()!
u/yonatan

nice golf, r=(t+i)**3.9%1 works too
u/tomxor

Yeah I was surprised to, I think this one is a bit more sensitive to bad distributions. Yonatan's is pretty good though.
u/pavel

X=t?X+r*50:0 -> X=t&&X+r*50
u/pavel

r=++t**3.9%1 saves 3 chars
u/pavel

Ah, no, it kills the sky/water.
u/KilledByAPixel

i feel it is possible to somehow golf the random part by at least a byte but I still haven't found a way without major issues
u/pavel

for(X=t&&X+r*25,i=h=11+6*C(t*4+X%1)<<5;--i;x.fillRect(...t?[X-r*i/8,600+(r*8&3?i-h:h-i),i/4,2]:[i*8,r*600,h,r]))r=1+S(i^X)
u/pavel

122
u/KilledByAPixel

I knew you could do it pavel!
u/aleamb

beautiful!!

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tomxor

remix of d/21783 by u/tomxor

function u(t) {

A=t?A.map(a=>(s=u[a>>4]^=1,x[s?'fillRect':'clearRect'](a>>6,a&1008,16,16),a=a+2*s+1&~4,a+=a&1?a%4-2<<10:a%4-1<<4)):[54675,69010,69233,54896]

Mar 2 2021 11:27 PM UTC

}// 140/140

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Multi #langton's #ant

u/tomxor

Squashed each ant into a 16bit bit field, [X,Y,D] = 0b 111111 111111 0111. These ants were generated with: X=7,Y=7,D=0,[[-X,-Y,3+D],[+Y,-X,2+D],[+X,+Y,1+D],[-Y,+X,0+D]].map(([X,Y,D])=>X+60<<10|Y+32<<4|D%4<<0)
u/mark1626

This is incredible. Just one question, how does s = u[a >> 4] ^= 1 work?
u/tomxor

Thanks :) a>>4 is the cell index of a 64x64 grid. the lower 4 bits are for the ant's direction so shifting them off to the right leaves only the 12 X and Y bits (see above). u is just an object, so all of these indicies will be undefined initially, but undefined is falsey and bitwise operators coerce falsey into 0, i.e undefined ^ 1 == 0 ^ 1 == 1, in otherwords XOR just treats all of the initial cell values as 0. Using the assignment version ^= means we toggle each cell between 0 and 1 each time an ant passes through it (which is part of the langton ant rules).

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tomxor

remix of d/19945 by u/katkip

function u(t) {

c.style.background='#ff0'
for(i=t>.64&t<.94|t?0:8e2;i--;x.fillRect(960+k*S(i),540+k*C(i),s=6-2*S(S(i*2)*3)+(8422463>>t*60&2),s))k=(1-t)*480

Sep 14 2020 2:50 AM UTC

}// 139/140

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#Vinyl #LP #Record

u/aleamb

wow!

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tomxor

remix of d/18413 by u/pavel

function u(t) {

for(w=c.width=120,i=9e3;i--;x.fillRect(i%w,i/w,1+S(9*X/d)**5*S(9*Y/d)**5,d/2+Y/3))X=i%w/30-2,Y=i/w/30-1,r=X*X+Y*Y,d=r>1||1+(1-r)*S(r*9-t*4)

Apr 23 2020 1:15 AM UTC

}// 139/140

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u/aleamb

impressive! #render #witchcraft #raytracing #scene

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tomxor

function u(t) {

eval(unescape(escape`挮睩摴栽㈴〻挮獴祬攽❦楬瑥爺獥灩愨ㄩ楮癥牴⠱✻景爨椽㉥㐻椭ⴻ⥸⹦楬汒散琨ㄲ〫㔰⩓⡘㵩┱㈰⼳㤩⩃⡙㵩⼶攳⤭䌨夫琩⨨娽匨匨堯太㠫堪ㄶ⭴⨲⤫匨太㐩⭴⤩ⰶ㜫㔰⩃⡘⤭䌨堫琩⩚ⱓ⡘⤬䌨夫娯㈫堫琩⤻`.replace(/u(..)/g,"$1%")))

Mar 20 2019 12:56 AM UTC

}// 140/140

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Water World #planet #space

u/lionleaf

#compressed #shading I'm really enjoying all these space related dweets
u/tomxor

Thanks lion :) glad your enjoying them, I think i've almost run out of things ot map to pseudo spheres now though :P
u/rnbw

breathtaking

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tomxor

remix of d/25593 by u/KilledByAPixel

function u(t) {

for(i=1e3;i--;b=a)a=u[j=i%461]||[960,540],x.fillRect(a[0]+=0|3*S(r=j*1.0472),a[1]+=0|3*C(r),u[a]?u[j]=[...b]:u[a]=2,3)

Jun 8 2022 3:56 PM UTC

}// 118/140

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Smoler Isometric Divisions

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u/tomxor

Seems to be easier to find good results if j=i%461 is restricted to primes.
u/pavel

-4 for(i=1e3;i--;x.fillRect(a[0]+=3*S(r=j/.955)|0,a[1]+=3*C(r)|0,u[a]?u[j]=[...b]:2,u[b=a]=3))a=u[j=i%461]||[960,540]
u/KilledByAPixel

nice!
u/pavel

Weirdly the numeric error from approximating pi/3 seems to matter a lot.
u/tomxor

Yeah, I think it's because it causes a deviation in the sequence at j=0. Although the output of 0|3*C(r) generally gives the expected low period of +1,+2,+1,-1,-2,-1 as j decrements, it ends on a 3, but only when using lower precision PI/3. full precision PI/3 pushes all of the 2s into 3s, which can be corrected by lowering the coefficient to 2.9, but this also makes j=0 output 2 which then seems to destroy the complexity.
u/pavel

I tried getting rid of the sin/cos by using hex coordinates but I was unable to make a complex picture. Usually just one of the six slices drew-in.

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