Difference between revisions of "Byte Battle"

Revision as of 03:06, 19 December 2022

Byte Battles

Byte Battles are a form of live coding, similar to Shader Showdowns, where two contestants compete in writing a visual effect in 25 minutes. The coding environment is the TIC-80 fantasy console. However, unlike Shader Showdowns, there is an additional limit: the final code should be 256 characters or less. This requires the contestants to use efficient code (e.g. single letter variables) and to minimize the code (e.g. remove the whitespace), all within the time limit. Unlike in normal TIC-80 sizecoding, there is no compression, so every character counts.

General notation in this article

Basic optimizations

• Functions, that are called three or more times should be aliased. For example, e=elli with e()e()e() is 3 characters shorter than elli()elli()elli(). Functions with 5-character-long names may already benefit from aliasing with two calls: r=rectb with r()r() is 1 character shorter than rectb()rectb().
• t=0 with t=t+.01 is 1 character shorter than t=time()*.6.
• for i=0,32639 do x=i%240y=i/240 end is 2-3 characters shorter than for y=0,135 do for x=0,239 do end end.
• (x*x+y*y)^.5 is 6 characters shorter than math.sqrt(x*x+y*y).
• s(w-11) and s(w+8) both approximate math.cos(w), so only math.sin needs to be aliased. s(w-11) is far more accurate, with the cost of one more character.

One-lining

Most whitespace can be removed from LUA code. For example: x=0y=0 is valid. All new lines can be removed or replaced with space, making the whole code a single line:

function TIC()for i=0,32639 do poke4(i,i)end end

Warning: Letters a-f and A-F after a number cause problems. a=0b=0 is not valid code. It is advisable to only used one letter variables in the ranges g-z and G-Z from the start; this will make eventual one-lining easier.

Load-function

Function load takes a string of code and returns a function with no named arguments, with the code as its body. It's particularly useful for shortening the TIC function after one-lining:

TIC=load'for i=0,32639 do poke4(i,i)end'

As a rule of thumb, one-lining and using the load trick can bring a ~ 275 character code down to 256.

Any arguments passes to a function defined with load can be fetched with the ellipsis (...). For example, SCN=function(x)poke(16320,x)end can be implemented as:

SCN=load'poke(16320,...)'

This saves 6 characters. Multiple arguments can be fetched with x,y=....

Warning: The backslash causes problems when using the load trick. In particular, if you have a string with escaped characters in the original code e.g. print("foo\nbar"), then this needs to be double-escaped: load'print("foo\\nbar")'

Dithering

If you have a floating point color value, TIC-80 pix and poke4 functions round it (toward zero). To add dithering, add a small value, between 0 and 1, to the color. The best technique depends whether you have x and y available or only i and how many bytes you can spare:

Expression	Length	Result	Notes
			No dithering
i%.7	4
i^2.5%1	7		"random" dithering
s(i)*i%1	8		also "random" dithering
i*481/960%1	11		(x/2+y/4)%1 if you have x&y. i*25/96%1 or i*97/192 if desperate.
(x*2-y%2)%4/4	13		2x2 block dithering
(i*2-i//80%2)%4/4	17		2x2 block dithering (almost), from i only
(x*2-y%2)%4/4+((x&2)-y//2%2)%4/16	33		4x4 with expression defined dithering matrix defined by an expression
('0415627326158473'):sub(p,p)/8	44		4x4 with data-defined dithering matrix, p defined as p=y%4*4+x%4+1

A quick example demonstrating the 2x2 block dithering:

function TIC()
 cls()
 for i=0,2399 do
  x=i%240
  y=i//240
  poke4(i,x/30+(x*2-y%2)%4/4)
 end
end

Palettes

The following palettes assume that j goes from 0 to 47. Usually there's no need to make a new loop for this: just reuse another loop with j=i%48.

Expression	Length	Result	Notes
poke(16320+j,j*5)	17
poke(16320+j,j%3*j*5)	21		Good for objects & background
poke(16320+j,j%3*j/.4)	22		Use (j+1)%3, (j+2)%3 or 2*j%3 for different colors
poke(16320+j,s(j)^2*255)	24		Change the phase of the palette with s(j+p)
poke(16320+j,s(j)^2*j*6)	24		Change the phase of the palette with s(j+p)
poke(16320+j,s(j/15)*255)	25		s(j/15)^2 is less bright
poke(16320+j,s(j-j%-3)^2*255)	29		j%3*2 for a more blue/beige variant, -j%3*4 for beige/blue variant
poke(16320+j,255/(1+2^(4+j%3-j/5)))	35		2*j%3 for a pink variant
poke(16320+j,255/(1+2^(5-j%3-j/5)))	35		2*j%3 for a green variant
poke(16320+j,s(j/15+s(j%3*3))^2*255)	37		Cyclic, based on [1]

The last one is an entire family of palettes. You can replace s(j%3*3) with any function that depends on j%3; this ensures the palette remains cyclic. Some ideas for tweaking the palettes:

• Invert the colors by adding a -1- in the expression
• Flip the blue/red channels & have the entire palette running backwards by using poke(16367-j,...)
• Abuse the default Sweetie 16 palette, by only setting some of the RGB channels, while keeping others as they are. For example, setting all the blue channels to zero: poke(16322+j*3,0). Here j is between 0 and 15.

Code for testing palettes:

function TIC()
 cls()
 for j=0,47 do poke(16320+j,s(j/15)*255)end
 for c=0,15 do rect(c*5,0,5,5,c)end
end
s=math.sin

Motion blur

In TIC-80 API, the pix and poke4 functions round numbers towards zero. This can be abused for a motion blur: poke4(i,peek4(i)-.9) maps colors 1 to 15 into one lower value, but value 0 stays as it is. Like so:

function TIC()
 t=time()/9
 circ(t%240,t%136,9,15)
 for i=0,32639 do poke4(i,peek4(i)-.9)end
end

Updating only some pixels

Pixel-based effects, especially raycasting and raymarching, can become excessively slow. A simple trick to update only ~ half of the pixels, giving a dithered/motion blur look and making the update smoother:

function TIC()
 t=time()/499
 for i=t%2,32639,1.9 do poke4(i,i/4e3+t)end
end

Examples of effects

The effects have not been crunched to keep them readable.

Plasma

function TIC()
 t=time()/499
 for i=0,32639 do
  x=i%240
  y=i/240
  v=s(x/50+t)+s(y/22+t)+s(x/32)
  poke4(i,v*2%8)
 end
end
s=math.sin

Rotozoomer

function TIC()
 t=time()/999 
 a=s(t-11)
 b=s(t)
 for i=0,32639 do
  x=i%240-120
  y=i/240-68
  u=a*x-b*y
  v=b*x+a*y
  poke4(i,(u//1~v//1)//16)
 end
end
s=math.sin

Tunnel

function TIC()
 t=time()/199
 for i=0,32639 do
  x=i%240-s(t/7)*99-120
  y=i/240-s(t/9)*49-68
  u=math.atan2(y,x)*6/6.29
  v=99/(x*x+y*y)^.5+t
  poke4(i,u//1~v//1)
 end
end
s=math.sin

Raymarcher

The map is a bunch of repeated spheres here.

function TIC()
 for i=0,32639 do
  -- ray (u,v,w), not normalized!
  u=i%240/120-1
  v=i/32639-.5
  w=1
  -- camera origo (x,y,z)
  x=3
  y=0
  z=time()/999 -- camera moves with time
  j=0
  repeat
   X=x%6-3 -- domain repetition
   Y=y%6-3
   Z=z%6-3
   -- ray not normalized=>reduce scale
   m=(X*X+Y*Y+Z*Z)^.5/2-1
   x=x+m*u
   y=y+m*v
   z=z+m*w
   j=j+1
  until j>15 or m<.1
  poke4(i,j)
 end
end

Additional Resources

• Code from past bytebattles https://livecode.demozoo.org/