[Functions] Useful Lua

[Tai]

Just some random, interesting, maybe useful functions.


Splitting a String Array:

function split(str, separator)
   local t = {} 
   local fpat = "(.-)" .. separator
   local last_end = 1
   local s, e, cap = str:find(fpat, 1)
   while s do
      if s ~= 1 or cap ~= "" then
	 table.insert(t,cap)
      end
      last_end = e+1
      s, e, cap = str:find(fpat, last_end)
   end
   if last_end <= #str then
      cap = str:sub(last_end)
      table.insert(t, cap)
   end
   return t
end

Testing the String Prefix:

function startsWith(str, prefix) 
    local ret = false;
    if str ~= nil and prefix ~= nil then
        ret = string.sub(str,1,string.len(prefix))==prefix;
    end
    return ret;
end

Changing the Brightness of a Given Color:

function gradient (color, bright)
-- brightness is giving in times
    local R,G,B = color2rgb(color)
-- RGB -> HSV
    local MAX = R;
    local MIN = R;
    if MAX < G then
        MAX = G
    end
    if MAX < B then
        MAX = B
    end
    if MIN > G then
        MIN = G
    end
    if MIN > B then
        MIN = B
    end
    local H,S,V; 
    if MIN == MAX then
        H = 0;
    elseif MAX == R and G > B then
        H = 60  * (G-B) / (MAX-MIN)
    elseif MAX == R and G < B then
        H = 60  * (G-B) / (MAX-MIN) + 360
    elseif MAX == G then
        H = 60  * (B-R) / (MAX-MIN) + 120
    elseif MAX == B then
        H = 60  * (R-G) / (MAX-MIN) + 240
    end
    if MAX == 0 then
        S = 0;
    else
        S = 1 - MIN/MAX;
    end
    V = MAX;
 
    V = bright * V;
 
-- HSV -> RGB
    local Hi = math.floor(H/60);
    local f = H%60;
    local p = V*(1-S);
    local q = V*(1-f*S);
    local t = V*(1-(1-f)*S);
    if Hi == 0 then
        R = V; 
        G = t; 
        B = p;
    elseif Hi == 1 then
        R = q; 
        G = V; 
        B = p;
    elseif Hi == 2 then
        R = p; 
        G = V; 
        B = t;
    elseif Hi == 3 then
        R = p; 
        G = q; 
        B = V;
    elseif Hi == 4 then
        R = t; 
        G = p; 
        B = V;
    elseif Hi == 5 then
        R = V; 
        G = p; 
        B = q;
    end
    R =  math.floor(R * 255)
    G = math.floor(G * 255)
    B =  math.floor(B * 255)
 
    return core.rgb(R, G, B)
end
 
function color2rgb (color)
    local R = color % 256 / 255;
    local G = ((color - R) / 256) % 256 / 255;
    local B = ((color - R - G*256) /(256 * 256)) % 256 / 255;
    return R,G,B;
end

Gauss Error Function:

function erf(x) 
    local ret = 0;
    local t,z,ans;
    z = x;
    t = 1.0/(1.0 + 0.5*z);
    ans = t * math.exp( -z * z - 1.26551223
        + t*(1.00002368 + t*(0.37409196 + t*(0.09678418
        + t*( -0.18628806 + t*(0.27886807 + t*( -1.13520398 + t*(1.48851587
        + t*( -0.82215223 + t*0.17087277)))))))));   
    if x >= 0.0 then 
        ret = ans;   
    else 
        ret = 2.0 - ans;   
    end
    return 1.0 - ret;
 
end

Inverse Gauss Error Function:

function erfinv(y)
   if y > 1 or y < -1 then
    return 0;
   end
   local a ={};
   a[1] = 0.886226899;
   a[2] = -1.645349621;
   a[3] = 0.914624893;
   a[4] = -0.140543331;
   local b ={};
   b[1] = -2.118377725;
   b[2] = 1.442710462;
   b[3] = -0.329097515;
   b[4] = 0.012229801;
   local c ={};
   c[1] = -1.970840454;
   c[2] = -1.624906493;
   c[3] = 3.429567803;
   c[4] =  1.641345311;
   local d ={};
   d[1] = 3.543889200;
   d[2] = 1.637067800;
 
   local y0 = 0.7;  
   local  x, z;
 
    if math.abs(y) == 1.0 then 
        x = -y*math.log(0.0);   
    elseif y < -y0 then 
        z = math.sqrt(-math.log((1.0+y)/2.0));
        x = -(((c[4]*z+c[3])*z+c[2])*z+c[1])/((d[2]*z+d[1])*z+1.0);
    elseif y<y0 then 
        z = y*y;
        x = y*(((a[4]*z+a[3])*z+a[2])*z+a[1])/((((b[4]*z+b[4])*z+b[2])*z+b[1])*z+1.0); 
    else 
        z = math.sqrt(-math.log((1.0-y)/2.0));
        x = (((c[4]*z+c[3])*z+c[2])*z+c[1])/((d[2]*z+d[1])*z+1.0);     
    end     
    --polish x to full accuracy     
    x = x - (erf(x) - y) / (2.0/math.sqrt(math.pi) * math.exp(-x*x));     
    x = x - (erf(x) - y) / (2.0/math.sqrt(math.pi) * math.exp(-x*x));   
    return x;
end

 

[OTx]

Do you have any examples with these functions? Else, it's pretty good.

 

[Tai]

Do you have any examples with these functions? Else, it's pretty good.

Not necessarily, splitting a string and testing the string prefix can be useful for OpenTibia Lua, but the others are just examples of what exactly Lua can do.