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Week of the 15/06/2020 - #25
Contents
Tech
- Path tracing in Shadertoy
- Vulkan resources
- More sizecoding
Science
- Notes on rendering 2D patterns
- Darwin’s first—and only—trip around the world began a scientific revolution
Path tracing in Shadertoy
I found this very good 3 part series on doing path tracing using Shadertoy. The article walks you on how these three images are rendered.
The articles are here:
- Casual Shadertoy Path Tracing 1: Basic Camera, Diffuse, Emissive - [article] [Shadertoy]
- Casual Shadertoy Path Tracing 2: Image Improvement and Glossy Reflections [article] [Shadertoy]
- Casual Shadertoy Path Tracing 3: Fresnel, Rough Refraction & Absorption, Orbit Camera - [article] [Shadertoy]
Notes on rendering 2D patterns
While working on my experiments on the Apple II, I needed to generate a pattern of tiles that even though is symetric in both x and y axis its made up from a pattern that repeats itself in a smaller structure. What you need to do is take the smallest repeatable element and calculate on what coordinates to put the elements. Lets see an example:
If you have a closer look you’ll notice that there is an element that repeats but it’s a little tricky to pinpoint what it is. Once you have identified the element you can trace it to get a better idea of where it repeats. Now you need to calculte the coordinates in the grid of where it will appear. For this you need to identify two vectorsthat translate the pattern. The important thing is that they are not parallel. Once you have these two vectors (Lets call them e1 and e2) you can specify any element in the grid as v = n e1 + m e2 where n and m and integers.
In the example e1 = (3,3) and e2 = (7,-1). To to get the x and y coordinates of our pattern we have:
x = 3n + 7m y = 3n - m
Vulkan resources
A list of a couple of resources I foud on Vulkan 3D technolgy
- Vulkan Tutorial - [web] [pdf] [epub]
- Vulkan Guide - “The Vulkan Guide is designed to help developers get up and going with the world of Vulkan. It is aimed to be a light read that leads to many other useful links depending on what a developer is looking for. All information is intended to help better fill the gaps about the many nuances of Vulkan.” [GitHub]
- Vulkan Samples - The Vulkan Samples is collection of resources to help you develop optimized Vulkan applications. [GitHub]
Darwin’s first—and only—trip around the world began a scientific revolution
The Nation Geographic site has a great article con Darwin’s expedition: “The plants and animals encountered on the five-year voyage of the ‘Beagle’ provided the foundation for Charles Darwin’s theory of evolution.”. The article is filled with drawings, paintings, infographics and photos of objects. You can see it here. Take a look at this great slideshow
More Sizecoding
Today I watched a cool Twitch video by Filipe Cruz (a.k.a. psenough) with a couple of cool sizecoders talking about 256b demo coding. This is the Twitch video and herer are some of the demos mentioned which I would like to investigate:
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; /\______ /\______ /\________
; __\\\___ \_ __\\\___ \_ __\\\______ \
; | / / | / / | _____/ \_
; | / /____| / /____| \ |
; | \____ : _____/ : \ |
; | / \ \ |
; | / . \ . \ |
; __ _|_ / \ \ _|_ __
; \ \\_\ \\__\ _/ : \_ : \_ /__// /_// /
; |____/_ _ :______ _ :______ _ |
; \\\____________| \\\____________| \\\____________|
;
; _______ _______ _______ _______ _______ _______
; _\\\__ \___\\\__ \___\\\__ \___\\\_____ \___\\\_____ \___\\\__ \_
;| /______/| / /| / /| / | / | / /
;\ | / /_| / /_| / | / | / /_
;|\_______ : _____/ : \_____/ : / : / : \____ |
;| / . \ . \ . / . / . / |
;| / \ \ / / |
;|___ :___ :___ :___\ :___ :___/ sns |
; \\_________: \\_________: \\_________: \\_________: \\_________: \\_________|
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; R E D S E C T O R I N C
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; Metropole a 256 bytes intro by Baudsurfer/RSI 2015 aka olivier.poudade.free.fr
; Presented first at the Function 2015 demoscene demo party in Budapest Hungaria
; Greets Blabla Conscience Bon^2 BReWErS CODEX Flush Lineout Mandarine Onslaught
; Paranoimia Quartex Rebels Razor1911 RiOT Titan and to all assembly programmers
; rsi.untergrund.net twitter.com/red_sector_inc facebook.com/redsectorinc ircnet
; RSI asciilogo by sEnsER/BRK vidcap youtube.com/watch?v=Z8Av7Sc7yGY by Fra/MDRN
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b equ byte ; tested on xp, freedos, ms windows dos and its debug
w equ word ; short form pretty-print helpers datatype specifiers
org 100h ; entering ip=cs:256 just above .com psp 127-byte dta
mov fs,ax ; ax=0? was pop bp before rewrite for non-zero fs seg
pop bp ; bp=0 cs:[0fffeh]=ss:[sp]=0000 if not debug executed
mov al,13h ; function switch to video mode 13h 320x200x256 & cls
int 10h ; general video bios service for all mode 13h vga api
push w 0a000h ; was les cx,[bx] es=9fffh cx=20cdh & lea ax,[di-10h]
pop es ; ms-dos v6.22 or freedos not "les rr,[0]" compatible
a:test bp,100h ; script idx bounds reached? bp E [0;255] i.e aam 255
jz c ; if hibyte OR rollover sign propagated to hibyte lsb
xor b[c],8h ; xor mutex modify next opcode to keep idx normalized
c:dec bp ; follow through and advance script idx dec bp/inc bp
e:mov cx,0ffh ; cl=visibility fostrum, null ch implicit object mask
g:cwd ; shorter xor dx,dx with ah<128 for div moved for agi
mov si,140h ; vga vid mode 19 horizontal scanline width in pixels
mov bx,cx ; bl=distance nullify bh raymarch object height limit
mov ax,di ; di=beam spot absolute vga coord, no dos para fix-up
not bl ; bl=distance/z axis orientation= -visibility fostrum
div si ; main 3d projection returns with ax=y dx=x ; dh = x
call q ; main 3d projection returns withah=(y-y0)*z ; bl = z
call q ; main 3d projection returns withah=(x-x0)*z ; ah = y
mov si,46ch ; 46ch=bda rtc off in zero seg plus ad hoc off buffer
add bl,[fs:si] ; bl=z+=rtc word in bda advances camera, assumed fs=0
adc dh,[si] ; dh+=beam spot camera x coordinates cs/ds:46ch & rtc
add ah,[si+1] ; ah+=beam spot camera y coordinates cs/ds:46dh & rtc
mov al,dh ; push/pop preserve texture x>>8 texel base for later
adc ch,al ; this object's implicit form xor /w building overlay
and dh,bl ; dh=x bl=x i.e x+=y bh and dl used as generic params
mov bh,30h ; bh=y height max of overpass, function generic param
mov dl,20h ; dl=y height min of overpass, function generic param
call r ; function returns if this object or building ray hit
jz h ; if objects volume intersect with ray texture former
push bx ; preserve prev rtc time to avoid costly seg override
mov dl,10h ; dl=y height max of spaceship function generic param
mov bh,14h ; bh=y height min of spaceship function generic param
sub bl,[fs:si] ; bl=z+=rtc word in bda advances spaceship1 camera<--
sub bl,[fs:si] ; bl=z+=rtc word in bda advances spaceship1 camera<--
xor ch,ch ; flag differenciates between spaceship* and overpass
call r ; function returns if this object or building ray hit
pop bx ; restore prev rtc time also implicit ch val returned
jz h ; if objects volume intersect with ray texture former
mov dl,18h ; dl=y height max of spaceship function generic param
mov bh,1ch ; bh=y height min of spaceship function generic param
add bl,[fs:si] ; bl=z+=rtc word in bda advances spaceship2 camera-->
call r ; function returns if this object or building ray hit
jz h ; if objects volume intersect with ray texture former
loop g ; if no object volumes intersect then continue z rays
h:xchg ax,dx ; texture subroutine - clone ray collision height val
cmp dh,40h ; test if this ray collision height val is exactly 64
jz l ; process as scenery bottom floor, al=depth was saved
pushf ; ax disposed of in z-buffer order override data flow
pop ax ; subroutine marked eflags /w bit10 df=spaceship true
sahf ; convert this object's bit10 df to pf for conditions
jp k ; if z-ray collided with a spaceship object then exit
test cl,cl ; else test if ray collision exited on loop condition
jz i ; if distance=0=>no scenery intersection=open horizon
inc dh ; test if this ray collision height=top=255=sky limit
jnz j ; else ray hit other scenery building/overpass object
i:mov al,0ffh ; is sky so apply old b/w film rear projection effect
jmp m ; with brightest standard vga palette grayscale color
j:and al,bl ; is building/overpass process texel window step #1/3
xor al,dh ; is building/overpass process texel window step #2/3
xor dl,bl ; is building/overpass process texel bricks step #1/2
and dl,dh ; is building/overpass process texel bricks step #2/2
shl al,02h ; is building/overpass process texel window step #3/3
and dl,01h ; test for building/overpass window or bricks texture
cmovnz ax,cx ; if window texel then color val=distance 586+ opcode
mov ah,0ffh ; colour for window or bricks of building or overpass
sub ah,al ; is dynamic for windows and static for all other obj
k:mov al,ah ; thunk for building/overpass/window/bricks/spaceship
jmp m ; proceed to last step of grayscale color normalizing
l:not ah ; floor grey bicolor flat-shaded for building shadows
and al,ah ; floor color multiplexes shadow depth=k*(255-height)
m:cld ; common thunk nullifies next spaceship=true obj flag
aam 12h ; normalize with dithering add overlap ah=color/18+00
mov al,16 ; normalize with dithering add overlap ah=color/18+16
aad 1 ; dithering normalized and prepare for next frame cwd
test di,di ; test for all pixels plotted overrunning vga segment
jp o ; preserve zf flag and test if absolute beam position
inc ax ; parity even augmenting lighting for odd meta-pixels
o:stosb ; write screen pixel & advance absolute beam position
jnz e ; if dst idx then continue automatic vga wrap-up fill
mov w[si],3711h ; post-assigns camera fixed value coordinates (17,55)
mov w[fs:si-1ch],1701h ; bda mem vid page 0 title curs position col=1 row=24
mov ah,9 ; dos 1+ write $ terminated string to standard output
mov dx,p ; hardcoded 24h terminated ascii string of demo title
int 21h ; general ms-dos api /w function 9 print ds:dx string
jmp a ; process next demo frame (sorry no escape sequence!)
q:xchg ax,dx ; 3-axis rotations require 2-axis ah=dh=x dh=(y-y0)*z
sub ax,bp ; translate to demo script idx arbitrary origin bp,bp
imul ax,bx ; project abcsisses/ordinates ah=(x-x0)*z dh=(y-y0)*z
add ax,67fh ; translate back to ~center=k*sqr(2) arbitrary fix-up
ret ; --------------------------->return to caller (0c3h)
r:push ax ; isosurface discrimination preserve building overlay
test bl,40h ; is it time~depth (i.e z+rtc) displaying an overpass
jnz v ; if not then process default buildings intersections
cmp ah,bh ; is y height>min of spaceship/overpass generic param
jnc v ; if not then process default buildings intersections
cmp ah,dl ; is y height<max of spaceship/overpass generic param
jc v ; if not then process default buildings intersections
test bl,78h ; is spaceship/overpass 120<z depth<128 static params
jnz u ; if not then process modified building intersections
test ch,ch ; flag differenciates between spaceship* and overpass
jnz t ; if overpass then proceed to translate it vertically
test al,78h ; is spaceship only objects 120<x width<128 in static
jnz u ; if not then process modified building intersections
std ; is spaceship and visible so set df flag accordingly
t:add ah,18h ; translate spaceship/overpass objects vertically +24
u:xor ah,ch ; this object's implicit form xor /w building overlay
v:test dh,10h ; alternate scene vertical irregularity every step 16
jnz x ; i.e : _||_||_||_||_||_||_||_||_||_||_||_||_||_||_||
add dh,al ; reduce scene horizontally = strech scene vertically
x:or ah,dh ; induce scene horizontal "y-colinear" irregularities
sahf ; implicit isosurface volume x AND y AND z AND 64=64?
pop ax ; isosurface discrimination preserve building overlay
ret ; --------------------------->return to caller (0c3h)
p db "megapole$" ; hardcoded 24h terminated ascii string of demo title
- Color Show - TomCatAbaddon [Pouet]
The author of Color Show has some other great demos. Here’s his [Pouet] profile.
A cool C64 demo
These are links to Filipe Cruz social networks and sites.