Difference between revisions of "Byte Battle"

Revision as of 12:36, 18 February 2022

Bytebattles

Bytebattles 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 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+.1 is 3 characters shorter than t=time()/399.
• 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.

load can be even used to minimize a function with parameters: ... returns the parameters. For example, the following example saves 3 bytes:

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

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
s(i)*99%1	9		"random" dithering, use *9 if desperate
i*481/960%1	11		chess horse, (x/2+y/4)%1 if you have x&y
(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

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/.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+2*j%3)^2*255)	30		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. 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

Any of the palettes can be quickly inverted by adding a -1- in the expression. It's also possible to just "tune" the default Sweetie 16 palette, for example by setting all the blue channels to zero: poke(16322+j*3,0). Here j is between 0 and 15.

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 at 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

Basic raymarcher

The basic structure for a raymarcher that has not been crunched to keep it readable. 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/