Lua Programming Help Thread

[andyauff]

That's it. And I still haven't changed it; it works. Haha.

[Eelim]

Hi everyone,

just need a little advice, i recently picked up lua for coding
(since i can't be arsed to install cygwin and all the other stuff
for coding in C for the psp), since this is a new language for me
i rely a lot on tutorials for learning how lua works, but for the problem
i have at the moment i cant find anything on the net, and the searchfunction
wasn't helpfull either...

oh, yeah, i almost forgot :-) here my problem:

i load several sets of sounds in variables which looks like this:

s1 = Sound.load("1a.wav")
s2 = Sound.load("1b.wav")
s3 = Sound.load("1c.wav")
s4 = Sound.load("1d.wav")

my problem now is, in some sound sets there might not be a "1b.wav",
my question is, how can i check if the file exists before i load it, so i can
load another file if there is none ?

greetings
Eelim

[FaT3oYCG]

this is untested but I'm sure that upon an error luaplayer returns nil so this may work

if s2 == nil then
s2 = whichever default file you want it to be
end

oh ye and could you please use (code) and (/code) tags it makes things easier to read thanks - replace the brackets with square brackets

if that works then i just had an idea this code may be better than that code as it checks for an error or not

if s2 == nil then
s2 = Sound.load("default.wav")
else
s2 = Sound.load("1b.wav")
end

to make it more efficient you could make a function that checks if the result is nil and if it is to use the default file and if not then load the file originally suggested

function sound_check(variable, sound_file)

if variable == nil then
variable = Sound.load("default.wav")
else
variable = Sound.load(sound_file)
end

end

to call that function for example you would use

sound_check(s2, "b1.wav")

to make it so you only have to type the name of the file the code would be this

function sound_check(variable, sound_file)

if variable == nil then
variable = Sound.load("default.wav")
else
variable = Sound.load("sound_file")
end

end

to call that function for example you would use

sound_check(s2, b1.wav)

this would mean that if the file does not exist then it would set that variable as default.wav but if that file does exist then it will set the variable to the sound file you told it to originally and you don't have to set the variable at the beginning of the program i don't think so then with this code you could just use

sound_check(s2, b1.wav)
s2:play()

all of the above are untested if they don't work come back here to get some more help

thanks

[eldiablov]

No. You would type

if s1 = nil then 

put rest of code here

[FaT3oYCG]

ok sorry i will change that thanks

EDIT:

revised and improved code with more options

thanks

[Eelim]

sorry, thats not it, your code would work if i just don't know if i have
loaded a file into the variable or not.
But the error occurs while trying
to load a file, not while trying to play it.

s2 = Sound.load("sound2.wav")

stops the player if the file is not on the memorystick, so i can't check if
s2 would be nil, cause the has player already stopped.

so what i need is either

a) The syntax to access the file system and look if the filename exists

or

b) the syntax for global errorhandling so i can prevent the player from halting.

greetings
Eelim

[FaT3oYCG]

hmm i have had many problems with music files and such before sometimes i dont know why but if you load a file e.g. a music file or a picture file after line 32 it crashes so separate your files into different lua files for example

sounds.lua - load all sounds in this file
pictures.lua - load all pictures in this file

and then in your main file normally your index.lua put

dofile("sounds.lua")
dofile("pictures.lua")

and it should work if not it is probably an error because of how long the file takes to load

as you cannot do something like this
s2 = Sound.load("sound2.wav")
s2:play()

also this code

function sound_check(variable, sound_file)

if variable == nil then
variable = Sound.load("default.wav")
else
variable = Sound.load("sound_file")
end

end

will check if the file exists or not - just call the function and pass the variable name and file name and it will see if the file is there if it isn it returns nil so then will handle the error accordingly to the code thereafter



to handle errors the error will display a message to the user but a nil statement will be passed before hand so you can ask if nil has been passed as shown above

[Eelim]

doesn't work,

if i use that code it always plays the default file, no matter if
the wanted file exists or not, cause since the variable is "new"
it is always nil, if i declare it before i call the function the player
stops if my wanted file does not exist. if i declare the variable
with a placeholder it is never nil, now the player tries again to
load the file and stops if it doesnt exist.

so again:
i need to know if the file exists on the memory stick BEFORE i
try to load it with "Sound.load".

how do i do that??

greetings
Eelim

[FaT3oYCG]

well you could replace that function to detect a file it is quite simple you could have modified it yourself but here it is

function file_check(path)

if path == nil then
s2 = nil
end

end

path example e.g. for path "ms0:/PSP/GAME/LuaPlayer/application_directory/music_file.wav"

and then you could just leave s2 as a blank variable

or change it to a default file

hope that helps come back if not

thanks

[TuxThePenguin]

Eldiablov - No. It's

if blah == nil

In comparisons a double = is used. Single is for setting a variable equal to something.

However, that's not even the best way to do it. A better way to do it would be

if not blah

[FaT3oYCG]

dont worry tux i realized that it was two not one thanks ne way and i think it was because that is what i originally had mine as but then i changed it

and how would we use an if not statement for this situation - enlighten me please

[Anti-QuickJay]

He already gave you a example. Use your Lua skills since your an expert now.

[FaT3oYCG]

He already gave you a example.

i didn't find if not blah very useful i only asked how it could be used if it makes you fell better ill ask again in more detail

hi TuxThePenguin could you please give me a detailed example of how the if not statement could be used to find out if a file exists

thanks

happy now A-QJ ??????

[Anti-QuickJay]

Learn how to check if a file exists. Then learn how to use a if not statement.
Learn Lua.

Now I'm happy :)

[Eelim]

hi, me again

function file_check(path)

if path == nil then
s2 = nil
end

end

this cannot work, same reasons as above, you are telling the
variable it is something when you call the function, so it is never nil,
and it does not check the memory stick if a file exists or not.

what i want to do is a "File Operation" on the "File System", classical
Input Output operations, and after more than 10 hours of searching
the net, i finally found the syntax for doing so.

so here is the code to check if a file exists on the memorystick or not
if someone should happen to have the same problem

function file_check(filename)
    f = io.open(filename)

    if f == nil then
        screen:print(100,100,"No such file exists")
    else
         screen:print(100,100,"File Found")
         f:close()
    end

end

file_check("test.wav")

greetings
Eelim

[FaT3oYCG]

Learn how to check if a file exists. Then learn how to use a if not statement.
Learn Lua.

Now I'm happy :)

i can cope with that


well done Eelim for solving your problem

and thanks for posting the answer not many people bother too

[FaT3oYCG]

Eelim i dont know if you will check this but i feel so stupid now that i know your problem and the result that you wanted this will let you check for a file

assert()

so to make a file check function

function file_check(file_path)
file = assert(io.open(file_path))
if file == nil then
screen:print(10, 10, "the file path was invalid")
else
screen:print(10, 10, "the file path was valid")
end
end

by using assert there is no need to actually open the file or close it so it should be much quicker

you can also return custom error messages using this command and create an error handler for your programs

- i dont have an example error handler but this is sort of how assert is used

if condition then
assert(test, "message")
end

this code means that if the condition is met then it will carry out the assert command so say if file == nil then you would use

if file == nil then
assert(file == nil, "this file is invalid")
end

if there is no message then the command can be used to check values and will return either false or nil so if the error or condition is false it wont be executed, but if it is nill it will assert the command given

- an example of this is the code used at the top of my post

that is the part of the code that is seen as the test

io.open(file_path)

in the top post no message was passed

the error messages come out the same was as if an error is returned in lua player with a black screen and a white error message

thanks

[Eelim]

hi,

i just didn't know lua had an assert command, for the things
i do now, it's ok the way i do it, cause if the file exists i have to
open it anyways, but for more complex structures assert is a
big win.

thx for the info!!!

i am a software engineer for over 10 years now, and i know several languages,
but i am new to lua, and one of my biggest problems is, i can't find
anything decent on the net on lua syntax, sure there are thousands
of tutorials, but 99,9% deal with the basic hello world, almost no
advanced tutorials, and if you manage to find something more advanced,
its usually unreadable (explaining every line of code, but not displaying,
the whole thing, so that you loose track of what the code actually does,
or yellow text on white background.. stuff like that..)

but anyways, thx a again for the assert info, that is a big help

greetings
Eelim

[Judas]

hi,

i just didn't know lua had an assert command, for the things
i do now, it's ok the way i do it, cause if the file exists i have to
open it anyways, but for more complex structures assert is a
big win.

thx for the info!!!

i am a software engineer for over 10 years now, and i know several languages,
but i am new to lua, and one of my biggest problems is, i can't find
anything decent on the net on lua syntax, sure there are thousands
of tutorials, but 99,9% deal with the basic hello world, almost no
advanced tutorials, and if you manage to find something more advanced,
its usually unreadable (explaining every line of code, but not displaying,
the whole thing, so that you loose track of what the code actually does,
or yellow text on white background.. stuff like that..)

but anyways, thx a again for the assert info, that is a big help

greetings
Eelim

You've been a software engineer for over 10 years, and can't figure out something as simple as going to Lua.org and learning the syntax? That's pretty hard to believe.

[eldiablov]

VERY hard to believe

Anyway you could go to www.evilmana.com for information on lua etc

~Sullivan~

[Eelim]

on lua.org everything concerning the io system has a big fat "TODO"
written under the topic, so no help there, evilmana is nice,
but not very readable (but good tutorials none the less), but
also nothing on the io system.

i wouldn't have asked here, if it was as simple as going to lua.org, think before you diss.

greetings
Eelim

[FaT3oYCG]

not to offend you but where have you been looking dont use lua.org use the official lua users wiki

http://lua-users.org/wiki/IoLibraryTutorial

go here for all of the directories and examples - most are filled in

http://lua-users.org/wiki/TutorialDirectory

IO defo is

[yaustar]

on lua.org everything concerning the io system has a big fat "TODO"
written under the topic, so no help there, evilmana is nice,
but not very readable (but good tutorials none the less), but
also nothing on the io system.

i wouldn't have asked here, if it was as simple as going to lua.org, think before you diss.

greetings
Eelim

http://www.lua.org/manual/5.1/manual.html#5.7
Lua.org -> Documentation -> Reference Manual -> IO

http://www.lua.org/pil/21.html
Lua.org -> Documentation -> Programming in Lua -> The first edition is available online! -> The IO library

http://lua-users.org/wiki/IoLibraryTutorial
Lua.org -> Community -> Wiki -> LuaTutorial -> TutorialDirectory -> IoLibraryTutorial

http://www.evilmana.com/tutorials/lua_tutorial_09.php
Evilmana.com -> Tutorials -> Lua for Beginners -> Reading and Writing Files

[FaT3oYCG]

ok then do use lua.org its more specific thanks yaustar we can always count on you

[Mistabeen]

I'm hoping someone can help me out here :)
This script works perfect on LUAplayer on my computer, but when testing it on the PSP it's a bit flawed.

What this does is read the color of the base map (PNG is not attached, but any PNG image image will do that's 480*272 and is only Black and white, other colors won't be seen anyway ) or you could always replace it with any other shape blitted to the screen instead of loading the image. According to the collor spotted it will either "collide" and not be able to move, or get damaga or heal.

It's something I'm working on so people who don't know LUA can easely "paint" their own levels with collision detection.

The only problem is, the collisions get detected a bit slow on the PSP. On the computer it works just fine, but on PSP sometimes it detects the collision as soon as you enter a black field, but somtimes it detects it afther a few pixels and you will get stuck as a result

It seems to be happening most when you have been moving around for a few seconds without colliding with an object, when you stand still in front of an object and then press an arrowbutton it'll collide instantly.

Does anyone know how to solve this?

Spoiler for Collision Script:

-- Easy Collisions --
-- Author: Mistabeen --

--var--
red = Color.new(255,0,0)
white = Color.new(255,255,255)
black = Color.new(0,0,0)
pink = Color.new(255,0,240)
green = Color.new(0,255,0)
map = Image.load( 'collide.png' )
posX = 300
posY = 100
mspeedL = 1
mspeedR = 1
mspeedT = 1
mspeedB = 1
hp = 100


-- main loop --
while true do
screen:clear(white)
pad = Controls.read()

-- movement --
-- You might want to change posX > Value according to the "speed" of your object,
-- if your detecting pixels go offscreen the script will crash
-- When you are making the background scroll instead of the player
-- you don't need to worry about these values and just delete them
if pad:left() and posX > 17 then
posX = posX - mspeedL
end

if pad:right() and posX < 463 then
posX = posX + mspeedR
end

if pad:up() and posY > 17 then
posY = posY - mspeedT
end

if pad:down() and posY < 255 then
posY = posY + mspeedB
end
--end movement--

if pad:select() then
break
end

-- this shows your black and white map you created
-- as an alternative, you could blit the hitboxes of the location of enemies,
-- or user placed objects (RTS game as an example) in black on the screen instead of an image
-- this would create an interactive base image for easy collisions --
screen:blit(0,0,map)
-- This get's the colors from the map to know if your object is close to an edge or not
-- These are 8 possitions it takes the colorinformation from
-- This is used for the topdown view of a character (or isometric view)
-- You can add or remove pixels to suit your needs
topcol = screenixel(posX,posY-14)
topRcol = screenixel(posX+10,posY-9)
topLcol = screenixel(posX-10,posY-9)
Rcol = screenixel(posX+14,posY)
Lcol = screenixel(posX-14,posY)
botcol = screenixel(posX,posY+14)
botLcol = screenixel(posX-10,posY+9)
botRcol = screenixel(posX+10,posY+9)

-- Here you baisicly compare the detected collor to black
-- if the color is black, then the movement should stop
-- you can add and remove some of these restrictions to suit your needs

if topcol == black then
mspeedT = 0
elseif topcol ~= black then
mspeedT = 1
end

if botcol == black then
mspeedB = 0
elseif botcol ~= black then
mspeedB = 1
end

if Rcol == black then
mspeedR = 0
elseif Rcol ~= black then
mspeedR = 1
end

if Lcol == black then
mspeedL = 0
elseif Lcol ~= black then
mspeedL = 1
end

if topRcol == black then
mspeedT = 0
mspeedR = 0
end

if topLcol == black then
mspeedT = 0
mspeedL = 0
end

if botLcol == black then
mspeedB = 0
mspeedL = 0
end

if botRcol == black then
mspeedB = 0
mspeedR = 0
end

if topcol == pink then
mspeedT = 0
hp = hp-1
end

if topRcol == pink then
mspeedT = 0
mspeedR = 0
hp = hp-1
end

if topLcol == pink then
mspeedT = 0
mspeedL = 0
hp = hp-1
end

if Rcol == pink then
mspeedR = 0
hp = hp-1
end

if Lcol == pink then
mspeedL = 0
hp = hp-1
end

if botRcol == pink then
mspeedB = 0
mspeedR = 0
hp = hp-1
end

if botLcol == pink then
mspeedB = 0
mspeedL = 0
hp = hp-1
end

if botcol == pink then
mspeedB = 0
hp = hp-1
end

if botcol == green or botRcol == green or botLcol == green or Lcol == green or Rcol == green or topLcol == green or topRcol == green or topcol == green then
hp = hp+1
end

-- This is just for debugging purpose
screen:fillRect(posX-1, posY-1, 3, 3, red)
screen:fillRect(posX,posY-14, 1, 1, red)
screen:fillRect(posX+10,p osY-9, 1, 1, red)
screen:fillRect(posX-10,posY-9, 1, 1, red)
screen:fillRect(posX+14,p osY, 1, 1, red)
screen:fillRect(posX-14,posY, 1, 1, red)
screen:fillRect(posX,posY +14, 1, 1, red)
screen:fillRect(posX-10,posY+9, 1, 1, red)
screen:fillRect(posX+10,p osY+9, 1, 1, red)

screenrint(10,10,mspeedT,red)
screenrint(10,20,mspeedR,red)
screenrint(10,30,mspeedL,red)
screenrint(10,40,mspeedB,red)
screenrint(10,50,"HP:"..hp,red)

screen.flip()
screen.waitVblankStart()

end

[Nielkie]

Instead of having so many variables, use more functions.

This could help:

function CollisionCheckLineColour(x1,y1,x2,y2,colour,img) --Only works with straight lines
	img = img or screen
	local colliding = false
	local test1;
	local test2;
	local NotTest;
	local step;
	if x1 == x2 then
		test1 = y1
		test2 = y2
		NotTest = x1
	elseif y1 == y2 then
		test1 = x1
		test2 = x2
		NotTest = y1
	end
	
	
	if test1 < test2 then
		step = 1
	else
		step = -1
	end
	for i=test1,test2,step do
		if img:Pixel(NotTest,i) == colour then
			colliding = true
		end
	end
	return colliding
end

function CollisionCheckBoxColour(x,y,width,height,colour,img)
	if CollisionCheckLineColour(x,y,x + width,y,colour,img) or
	  CollisionCheckLineColour(x + width,y,x + width,y + height,colour,img) or
	  CollisionCheckLineColour(x,y + height,x + width,y + height,colour,img) or
	  CollisionCheckLineColour(x,y,x,y + height,colour,img) then
		return true
	else
		return false
	end
end

[Mistabeen]

Thx Nielke, I'll take a look at it tomorow, it's a tad to late right now for me ^^ Thx tho

[Highsight]

Does anyone think they could convert this into an EBoot for me?

http://forums.qj.net/f-psp-developme...ml#post1915912

It needs LUAPlayer 0.16 MOD4. Last time I tried doing it, it didn't work at all. ;_;

[Anti-QuickJay]

These should work. I haven't tested.
http://www.sendspace.com/file/uvn88u

[Muhie]

Hi folks !
Im trying to make a little game, now i'm working on the beginmenu. I'm trying to load a background an tell the psp that if the cross button is pressed it should do file ./game.lua . But i get this error : Bad argument #2 to blit (image expected, got nil)

This is the code :

white = Color.new(255,255,255)
red = Color.new(255,0,0)
blue = Color.new(0,0,255)
orange = Color.new(255, 102, 0)

background = Image.load("images/begin.jpg")

oldpad = Controls.read()
while true do
pad = Controls.read()
screen:clear()
screen:blit(0,0,begin, true)
if pad:cross() then
dofile("./game.lua")
end

screen.waitVblankStart()
screen.flip()
end

I really hope you guys can help me !
Cheers.