Uh, let me reply quickly (I believe I'll have time to reply more deeply later) :
I see you're using BetterLuaAPI (), however it's been updated in FormulaPro (maybe I forgot to update it on its repo ), and here's the new version, using a good gc :


a_acute = string.uchar(225)
a_circ  = string.uchar(226)
a_tilde = string.uchar(227)
a_diaer = string.uchar(228)
a_ring  = string.uchar(229)
e_acute = string.uchar(233)
e_grave = string.uchar(232)
o_acute = string.uchar(243)
o_circ  = string.uchar(244)
l_alpha = string.uchar(945)
l_beta = string.uchar(946)
l_omega = string.uchar(2126)
sup_plus = string.uchar(8314)
sup_minus = string.uchar(8315)
right_arrow = string.uchar(8594)


Color = {
["black"] = {0, 0, 0},
["red"] = {255, 0, 0},
["green"] = {0, 255, 0},
["blue "] = {0, 0, 255},
["white"] = {255, 255, 255},
["brown"] = {165,42,42},
["cyan"] = {0,255,255},
["darkblue"] = {0,0,139},
["darkred"] = {139,0,0},
["fuchsia"] = {255,0,255},
["gold"] = {255,215,0},
["gray"] = {127,127,127},
["grey"] = {127,127,127},
["lightblue"] = {173,216,230},
["lightgreen"] = {144,238,144},
["magenta"] = {255,0,255},
["maroon"] = {128,0,0},
["navyblue"] = {159,175,223},
["orange"] = {255,165,0},
["palegreen"] = {152,251,152},
["pink"] = {255,192,203},
["purple"] = {128,0,128},
["royalblue"] = {65,105,225},
["salmon"] = {250,128,114},
["seagreen"] = {46,139,87},
["silver"] = {192,192,192},
["turquoise"] = {64,224,208},
["violet"] = {238,130,238},
["yellow"] = {255,255,0}
}
Color.mt = {__index = function () return {0,0,0} end}
setmetatable(Color,Color.mt)

function copyTable(t)
  local t2 = {}
  for k,v in pairs(t) do
    t2[k] = v
  end
  return t2
end

function deepcopy(t) -- This function recursively copies a table's contents, and ensures that metatables are preserved. That is, it will correctly clone a pure Lua object.
if type(t) ~= 'table' then return t end
local mt = getmetatable(t)
local res = {}
for k,v in pairs(t) do
if type(v) == 'table' then
v = deepcopy(v)
end
res[k] = v
end
setmetatable(res,mt)
return res
end -- from http://snippets.luacode.org/snippets/Deep_copy_of_a_Lua_Table_2

function utf8(nbr)
return string.uchar(nbr)
end

function test(arg)
return arg and 1 or 0
end

function screenRefresh()
return platform.window:invalidate()
end

function pww()
return platform.window:width()
end

function pwh()
return platform.window:height()
end

function drawPoint(gc, x, y)
gc:fillRect(x, y, 1, 1)
end

function drawCircle(gc, x, y, diameter)
gc:drawArc(x - diameter/2, y - diameter/2, diameter,diameter,0,360)
end

function drawCenteredString(gc, str)
gc:drawString(str, .5*(pww() - gc:getStringWidth(str)), .5*pwh(), "middle")
end

function drawXCenteredString(gc, str, y)
gc:drawString(str, .5*(pww() - gc:getStringWidth(str)), y, "top")
end

function setColor(gc,theColor)
if type(theColor) == "string" then
theColor = string.lower(theColor)
if type(Color[theColor]) == "table" then gc:setColorRGB(unpack(Color[theColor])) end
elseif type(theColor) == "table" then
gc:setColorRGB(unpack(theColor))
end
end

function verticalBar(gc,x)
gc:fillRect(gc,x,0,1,pwh())
end

function horizontalBar(gc,y)
gc:fillRect(gc,0,y,pww(),1)
end

function nativeBar(gc, screen, y)
gc:setColorRGB(128,128,128)
gc:fillRect(screen.x+5, screen.y+y, screen.w-10, 2)
end

function drawSquare(gc,x,y,l)
gc:drawPolyLine(gc,{(x-l/2),(y-l/2), (x+l/2),(y-l/2), (x+l/2),(y+l/2), (x-l/2),(y+l/2), (x-l/2),(y-l/2)})
end

function drawRoundRect(gc,x,y,wd,ht,rd)  -- wd = width, ht = height, rd = radius of the rounded corner
x = x-wd/2  -- let the center of the square be the origin (x coord)
y = y-ht/2 -- same for y coord
if rd > ht/2 then rd = ht/2 end -- avoid drawing cool but unexpected shapes. This will draw a circle (max rd)
gc:drawLine(x + rd, y, x + wd - (rd), y);
gc:drawArc(x + wd - (rd*2), y + ht - (rd*2), rd*2, rd*2, 270, 90);
gc:drawLine(x + wd, y + rd, x + wd, y + ht - (rd));
gc:drawArc(x + wd - (rd*2), y, rd*2, rd*2,0,90);
gc:drawLine(x + wd - (rd), y + ht, x + rd, y + ht);
gc:drawArc(x, y, rd*2, rd*2, 90, 90);
gc:drawLine(x, y + ht - (rd), x, y + rd);
gc:drawArc(x, y + ht - (rd*2), rd*2, rd*2, 180, 90);
end

function fillRoundRect(gc,x,y,wd,ht,radius)  -- wd = width and ht = height -- renders badly when transparency (alpha) is not at maximum >< will re-code later
if radius > ht/2 then radius = ht/2 end -- avoid drawing cool but unexpected shapes. This will draw a circle (max radius)
    gc:fillPolygon({(x-wd/2),(y-ht/2+radius), (x+wd/2),(y-ht/2+radius), (x+wd/2),(y+ht/2-radius), (x-wd/2),(y+ht/2-radius), (x-wd/2),(y-ht/2+radius)})
    gc:fillPolygon({(x-wd/2-radius+1),(y-ht/2), (x+wd/2-radius+1),(y-ht/2), (x+wd/2-radius+1),(y+ht/2), (x-wd/2+radius),(y+ht/2), (x-wd/2+radius),(y-ht/2)})
    x = x-wd/2  -- let the center of the square be the origin (x coord)
y = y-ht/2 -- same
gc:fillArc(x + wd - (radius*2), y + ht - (radius*2), radius*2, radius*2, 1, -91);
    gc:fillArc(x + wd - (radius*2), y, radius*2, radius*2,-2,91);
    gc:fillArc(x, y, radius*2, radius*2, 85, 95);
    gc:fillArc(x, y + ht - (radius*2), radius*2, radius*2, 180, 95);
end

The main difference, again, is about the gc usage.
Passing gc to the functions is the *only* way to do things well


I'll get back to your main problem soon (also calling jim )

@adriweb: Thanks for poiting to it, to be honest I haven't checked for updates in a long time . I just found this copy on my old harddrive, and used it I'm now using the updated version
[edit] it gives me an error: attempt to call method 'getStringWidth' (a nil value) nvm, it works now. Forgot to pass gc to it.

@Jim: Thanks, that fixed the problem! You really know pretty much everything about nspire lua it seems

Now I'm having a different problem (or maybe I'm trying to do something that can't be done):
function on.paint(gc)
 if screenNeedUpdate then
     for i=1,2 do
         for ii=1,5,1 do
             tile = string.sub(map[i], ii, ii)
             if tile == "G" then
                 gc:drawImage(tileGrass, tileGrass:width()*ii, tileGrass:height()*i )
             end
             if tile == "W" then
                 gc:drawImage(tileWater, tileWater:width()*ii, tileWater:height()*i)
             end
         end
     end
     refreshScreen()
     screenNeedUpdate = false
 end
endWhat I want to do is only update the screen when it is necesarry. I wanted to do this by setting a flag, screenNeedUpdate, with the idea being when this flag is true, that piece of code is executed and if not it isn't. The problem is,when I set the flag to true it paints everything but when set to false everything but on tile in the upper left corner disappears as soon as another key (or anything) happens.
[edit] they all disappear, the one staying there was because of wrongly placed code
[edit2] solved