advtrains.decode_pos

Decodes a Advtrains position string.

Note: this page has been written for Advtrains 2.0.1 TSS and Minetest 5.1.0. Examples and practices described in this page don't take advantage of improvements introduced in later releases.

advtrains.decode_pos(pts)

This function creates a string from the given Minetest position vector, suitable for use as a table index. See also advtrains.encode_pos.

• pts (string): a table index string created by advtrains.encode_pos.

A Minetest position vector.

It gives a runtime error if the pts parameter:

• is not at least 12 characters long
• contains characters not part of the hexadecimal notation

../mods/advtrains/advtrains/helpers.lua:373: attempt to perform arithmetic on a nil value
stack traceback:
    ../mods/advtrains/advtrains/helpers.lua:373: in function 'dec'
    ../mods/advtrains/advtrains/helpers.lua:388: in function 'decode_pos'
    ???:?: in main chunk
    [C]: in ?

This function converts back strings created by advtrains.encode_pos to their original vector form. Y, X and Z coordinates are treated separately: the corresponding parts of the argument are extracted and passed to dec, which converts the hexadecimal form of a number to its decimal form.

1. Y coordinate is encoded in characters 1 to 4.
2. X coordinate is encoded in characters 5 to 8.
3. Z coordinate is encoded in characters 9 to 12.

advtrains.decode_pos("800080008000") -- {x=0,y=0,z=0}
advtrains.decode_pos("807B7DC07F62") -- {x=-576,y=123,z=-158}
advtrains.decode_pos("1C401E5858F0") -- {x=-25000,y=-25536,z=-10000}

advtrains/helpers.lua, lines 383 to 389:

decode_pos.lua

-- DEPENDENCY CODE
local hext = { [0]="0",[1]="1",[2]="2",[3]="3",[4]="4",[5]="5",[6]="6",[7]="7",[8]="8",[9]="9",[10]="A",[11]="B",[12]="C",[13]="D",[14]="E",[15]="F"}
local dect = { ["0"]=0,["1"]=1,["2"]=2,["3"]=3,["4"]=4,["5"]=5,["6"]=6,["7"]=7,["8"]=8,["9"]=9,["A"]=10,["B"]=11,["C"]=12,["D"]=13,["E"]=14,["F"]=15}
 
local function c(s,i) return dect[string.sub(s,i,i)] end
 
local function dec(s)
    return (c(s,1)*4096 + c(s,2)*256 + c(s,3)*16 + c(s,4))-32768
end
-- [...]
 
function advtrains.decode_pos(pts)
    if not pts or not #pts==6 then return nil end
    local stry = string.sub(pts, 1,4)
    local strx = string.sub(pts, 5,8)
    local strz = string.sub(pts, 9,12)
    return vector.new(dec(strx), dec(stry), dec(strz))
end