Introduction to Scripting the GUI: Difference between revisions

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One important feature in MTA:DM is the ability to script customized GUI (Graphic User Interface). The GUI consists of windows, button, edit boxes, check boxes... Almost every standard form components in graphical environments. They can be displayed while the user is in game, and used for inputs and outputs in place of traditional commands.  
One important feature in MTA:SA is the ability to script customized GUI (Graphic User Interface). The GUI consists of windows, buttons, edit boxes, checkboxes... Almost every standard form components in graphical environments. They can be displayed while the user is in-game, and used for inputs and outputs in place of traditional commands.  


[[Image:AdminGUI.png|thumb|Admin Console GUI]]
[[Image:AdminGUI.png|thumb|Admin Console GUI]]


==A tutorial to make a login window==
==A tutorial to make a login window==
In this tutorial we'll make a simple login window, with two input boxes and a button. The window appears when the player joins the game, and once the button is clicked, the player is spawned. The tutorial will continue the gamemode we made in [[Scripting Introduction|Introduction to Scripting]]. We'll also take a look at client-side scripting.  
In this tutorial, we'll make a simple login window, with two input boxes and a button. The window appears when the player joins the game, and once the button is clicked, the player is spawned. The tutorial will continue the gamemode we made in [[Scripting Introduction|Introduction to Scripting]] ''(If you have used the [[Scripting Introduction|Introduction to Scripting]], you will need to remove or comment the [[spawnPlayer]] line in the "joinHandler" function in your code, as we will be replacing it with a GUI alternative in this tutorial)''. We'll also take a look at client-side scripting.  


===Draw the window===
===Draw the window===
All the GUI must be made client side. It is also a good practice to keep all the client scripts in a separate folder. Browse to /Your MTA Server/mods/deathmatch/resources/myserver/ directory, and create a folder named "client". Under /client/ directory, create a text file and name it "gui.lua", and in this file we will write a funtion that draws the window:
All the GUI must be made client-side. It is also a good practice to keep all the client scripts in a separate folder.  
 
Browse to /Your MTA Server/mods/deathmatch/resources/myserver/ directory, and create a folder named "client". Under /client/ directory, create a text file and name it "gui.lua".
 
In this file we will write a function that draws the window. To create a window we will use [[guiCreateWindow]]:
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
function CreateLoginWindow()
function createLoginWindow()
-- define the X and Y positions of the window
local X = 0.375
local X = 0.375
local Y = 0.375
local Y = 0.375
-- define the width and height of the window
local Width = 0.25
local Width = 0.25
local Height = 0.25
local Height = 0.25
-- create the window and save its element value into the variable 'wdwLogin'
-- click on the function's name to read its documentation
wdwLogin = guiCreateWindow(X, Y, Width, Height, "Please Log In", true)
wdwLogin = guiCreateWindow(X, Y, Width, Height, "Please Log In", true)
end
end
</syntaxhighlight>
</syntaxhighlight>
You may click on the function's name to read its documentation. Note that the coordinates of the window is in ''percentage'' of the screen. It means that if the screen is labelled with 0 on the left end, and 1 on the right end, and if "X" is 0.5, it represents the middle of the screen. It applies to Y, window width, and window height as well (if "width" is 0.5, the window will be half as wide as the screen). Next we'll add the text labels (saying "username:" and "password:"), edit boxes and a button. Replace the function with its complete version:
 
===Relative and Absolute===
Note that the final argument passed to guiCreateWindow in the above example is ''true''. This indicates that the coordinates and dimensions of the window are '''relative''', meaning they are a ''percentage'' of the total screen size. This means that if the far left side of the screen is 0, and the far right is 1, an X position of 0.5 would represent the center point of the screen. Similarly, if the top of the screen is 0 and the bottom is 1, a Y position of 0.2 would be 20% of the way down the screen. The same principles apply to both Width and Height as well (with a Width value of 0.5 meaning the window will be half as wide as the screen).
 
The alternative to using relative values is using '''absolute''' (by passing ''false'' instead of true to guiCreateWindow). Absolute values are calculated as the total number of pixels from the top-left corner of the parent (if no GUI element parent is specified, the parent is the screen itself). If we assume a screen resolution of 1920x1200, the far left side of the screen being 0 pixels and the far-right being 1920 pixels, an X position of 960 will represent the center point of the screen. Similarly, if the top of the screen is 0 pixels and the bottom is 1200, a Y position of 20 would be 20 pixels down from the top of the screen. The same principles apply to both Width and Height as well (with a Width value of 50 meaning the window will be 50 pixels wide). ''You can use [[guiGetScreenSize]] and a little maths to calculate certain absolute positions.''
 
The differences between using relative and absolute values are quite simple; GUI created using absolute values will always remain exactly the same pixel size and position, while GUI created using relative values will always be a percentage of its parent's size.
 
Absolute is generally easier to maintain when editing code by hand, however, your choice of type depends on the situation you are using it for.
 
For the purposes of this introduction, we will be using relative values.
 
===Adding the components===
Next, we'll add the text labels (saying "username:" and "password:"), edit boxes (for entering your data), and a button to log in.
 
To create buttons we use [[guiCreateButton]] and to create edit boxes use [[guiCreateEdit]]:
 
'''Note that we are now writing more code for our existing 'createLoginWindow' function. This is not a new function and is meant to replace what you already have.'''
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
function CreateLoginWindow()
function createLoginWindow()
local X = 0.375
local X = 0.375
local Y = 0.375
local Y = 0.375
Line 27: Line 52:
wdwLogin = guiCreateWindow(X, Y, Width, Height, "Please Log In", true)
wdwLogin = guiCreateWindow(X, Y, Width, Height, "Please Log In", true)
-- define new X and Y positions for the first label
X = 0.0825
X = 0.0825
Y = 0.2
Y = 0.2
-- define new Width and Height values for the first label
Width = 0.25
Width = 0.25
Height = 0.25
Height = 0.25
-- create the first label, note the final argument passed is 'wdwLogin' meaning the window
-- we created above is the parent of this label (so all the position and size values are now relative to the position of that window)
guiCreateLabel(X, Y, Width, Height, "Username", true, wdwLogin)
guiCreateLabel(X, Y, Width, Height, "Username", true, wdwLogin)
-- alter the Y value, so the second label is slightly below the first
Y = 0.5
Y = 0.5
guiCreateLabel(X, Y, Width, Height, "Password", true, wdwLogin)
guiCreateLabel(X, Y, Width, Height, "Password", true, wdwLogin)
X = 0.415
X = 0.415
Y = 0.2
Y = 0.2
Line 42: Line 73:
Y = 0.5
Y = 0.5
edtPass = guiCreateEdit(X, Y, Width, Height, "", true, wdwLogin)
edtPass = guiCreateEdit(X, Y, Width, Height, "", true, wdwLogin)
-- set the maximum character length for the username and password fields to 50
guiEditSetMaxLength(edtUser, 50)
guiEditSetMaxLength(edtUser, 50)
guiEditSetMaxLength(edtPass, 50)
guiEditSetMaxLength(edtPass, 50)
Line 51: Line 83:
btnLogin = guiCreateButton(X, Y, Width, Height, "Log In", true, wdwLogin)
btnLogin = guiCreateButton(X, Y, Width, Height, "Log In", true, wdwLogin)
-- make the window invisible
guiSetVisible(wdwLogin, false)
guiSetVisible(wdwLogin, false)
end
end
</syntaxhighlight>
</syntaxhighlight>
Note that every GUI component created is a child of the window, this is done by specifying the parent element (wdwLogin, in this case) when creating the component:
Note that every GUI component created is a child of the window, this is done by specifying the parent element (wdwLogin, in this case) when creating the component.
<syntaxhighlight lang="lua">
 
guiCreateLabel(X, Y, Width, Height, "Password", true, wdwLogin)
This is very useful because not only does it mean that all the components are attached to the window and will move with it, but also that any changes done to the parent window will be applied down the tree to these child components. For example, we can now hide all of the GUI we just created by simply hiding the window:
</syntaxhighlight>
This is very useful because later when you need to control the entire set of GUI, you can just refer to the parent element. For example:
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
guiSetVisible(wdwLogin, false) --hides all the GUI we made so we can show them to the player at the appropriate moment.  
guiSetVisible(wdwLogin, false) --hides all the GUI we made so we can show them to the player at the appropriate moment.  
Line 64: Line 95:


===Using the function we wrote===
===Using the function we wrote===
The CreateLoginWindow function is done, but it won't do anything until we call it. It is recommended to create all GUI when the client resource starts, hide them, and show them to player later when needed. Therefore, we'll write an event handler for "[[onClientResourceStart]]" to create the window:
The createLoginWindow function is now complete, but it won't do anything until we call it. It is recommended to create all GUI when the client resource starts, hide them, and show them to the player later when needed. Therefore, we'll write an event handler for "[[onClientResourceStart]]" to create the window:
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
addEventHandler("onClientResourceStart", getResourceRootElement(getThisResource()),  
-- attach the event handler to the root element of the resource
-- this means it will only trigger when its own resource is started
addEventHandler("onClientResourceStart", getResourceRootElement(),  
function ()
function ()
CreateLoginWindow()
createLoginWindow()
end
end
)
)
</syntaxhighlight>
</syntaxhighlight>
We would like to show the window when the client joins the game, using the same event "[[onClientResourceStart]]". Now the event handler looks like:
 
As this is a login window, we now need to show the window when the player joins the game.
This can be done using the same event, "[[onClientResourceStart]]", so we can modify the above code to include showing the window:
 
'''Note that we are now writing more code for our existing 'onClientResourceStart' handler. This is not a new event handler and is meant to replace what you already have.'''
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
addEventHandler("onClientResourceStart", getResourceRootElement(getThisResource()),  
addEventHandler("onClientResourceStart", getResourceRootElement(),  
function ()
function ()
CreateLoginWindow()
-- create the log in window and its components
createLoginWindow()


                 outputChatBox("Welcome to My MTA DM Server, please log in. ")
-- output a brief welcome message to the player
                 outputChatBox("Welcome to My MTA:SA Server, please log in.")


-- if the GUI was successfully created, then show the GUI to the player
        if (wdwLogin ~= nil) then
        if (wdwLogin ~= nil) then
        guiSetVisible(wdwLogin, true)
guiSetVisible(wdwLogin, true)
else
-- if the GUI hasn't been properly created, tell the player
outputChatBox("An unexpected error has occurred and the login GUI has not been created.")
        end  
        end  


-- enable the player's cursor (so they can select and click on the components)
        showCursor(true)
        showCursor(true)
-- set the input focus onto the GUI, allowing players (for example) to press 'T' without the chatbox opening
        guiSetInputEnabled(true)
        guiSetInputEnabled(true)
end
end
)
)
</syntaxhighlight>
</syntaxhighlight>
Note that we have a security check before making the window visible, so that in case the window had not been created, in which case wdwLogin is not a valid element, we don't get an error. The [[showCursor]] function gives control to your mouse, and [[guiSetInputEnabled]] makes sure when you type in the GUI, certain letters like "A", "S", "D", "W", "T" don't move your character or bring out the chatbox input. In the next step, we'll make the button work as desired.


===Scripting the button===
Note that we have a simple security check before making the window visible, so in the unlikely event that the window has not been created, meaning wdwLogin is not a valid element, we don't get an error and just inform the player what has happened.
When the player clicks on any part of the GUI, the event "[[onClientGUIClick]]" will be triggered for the GUI component you clicked on. For instance, if you click on the button, you can add the event handler attached to the button:
In the next step, we will create the button functionality for the login button.
 
==Scripting the button==
Now that we have created our GUI and shown it to the player, we need to make it work.
 
===Detecting the click===
When the player clicks on any part of the GUI, the event "[[onClientGUIClick]]" will be triggered for the GUI component you clicked on. This allows us to easily detect any clicks on the GUI elements we want to use.
For example, we can attach the event to the btnLogin button to catch any clicks on it:
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
addEventHandler("onClientGUIClick", theButtonElement, theHandlerFunction, false)
-- attach the event onClientGUIClick to btnLogin and set it to trigger the 'clientSubmitLogin' function
addEventHandler("onClientGUIClick", btnLogin, clientSubmitLogin, false)
</syntaxhighlight>
</syntaxhighlight>
In our script, we only need the event handler attached to the button. When it's clicked, the client will tell the server to spawn the player. Find the event handler code for "onClientResourceStart" from the previous section, and add the following line right AFTER CreateLoginWindow() is called:
'''Note the final argument passed is "false". This indicates that the event will only trigger directly on btnLogin, not if the event has propagated up or down the tree. Setting this to "true" while attaching to GUI elements will mean that clicking on any element in the same branch will trigger this event.'''
 
This line of code can now be added inside the createLoginWindow function. It is a common mistake to try and attach events to non-existent GUI elements, so make sure you always attach your events '''after''' the GUI element (in this case, the button) has been created:
 
'''Note that we are now writing more code for our existing 'createLoginWindow' function.'''
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
function createLoginWindow()
-- create all our GUI elements
...
-- now add our onClientGUIClick event to the button we just created
end
addEventHandler("onClientGUIClick", btnLogin, clientSubmitLogin, false)
addEventHandler("onClientGUIClick", btnLogin, clientSubmitLogin, false)
</syntaxhighlight>
</syntaxhighlight>
The event handler must be added here because it makes sure variable btnLogin contains the actual button. You cannot attach an event to an non-existant element. You should have noticed that we need the "clientSubmitLogin" function, as stated in the line above.
 
===Managing the click===
Now that we can detect when the player clicks on the button, we need to write code to manage what happens when they do.
In our [[onClientGUIClick]] event handle, we told it to call the function clientSubmitLogin whenever btnLogin is clicked.
Therefore, we can now use the function clientSubmitLogin to control what happens when the button is clicked:
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
function clientSubmitLogin(button)
-- create the function and define the 'button' and 'state' parameters
if button == "left" then
-- (these are passed automatically by onClientGUIClick)
function clientSubmitLogin(button,state)
triggerServerEvent("SubmitLogin", getRootElement(), guiGetText(edtUser), guiGetText(edtPass))
-- if our login button was clicked with the left mouse button, and the state of the mouse button is up
if button == "left" and state == "up" then
-- move the input focus back onto the game (allowing players to move around, open the chatbox, etc)
guiSetInputEnabled(false)
guiSetInputEnabled(false)
-- hide the window and all the components
guiSetVisible(wdwLogin, false)
guiSetVisible(wdwLogin, false)
-- hide the mouse cursor
showCursor(false)
showCursor(false)
end
end
end
end
</syntaxhighlight>
</syntaxhighlight>
The variable "button" is passed by the event handler, and it's a string with the name of the button (either "left" or "right"). Here we also hit a new concept, which is custom events. Custom events can be triggered by script from the same side (server to server, or client to client), or from the other side (server to client, or vice versa). Here we use the [[triggerServerEvent]] function to trigger a custom event on the server, "SubmitLogin".
Now, when the button is clicked, the window will be hidden and all controls will be returned to the player. Next, we will tell the server to allow the player to spawn.


At this point we have all the code needed on the client side. On the server side, recall that we are spawning the player as soon as they join, as shown below:
===Triggering the server===
Triggering the server can be done using [[triggerServerEvent]]. This allows you to trigger a specified event on the server from the client.
The same can be done in reverse using [[triggerClientEvent]].
Here, we use the [[triggerServerEvent]] function to call our own custom event on the server, named "submitLogin", which will then control the spawning of the player serverside.
 
'''Note that we are now writing more code for our existing 'clientSubmitLogin' function. This is not a new function and is meant to replace what you already have.'''
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
function joinHandler()
function clientSubmitLogin(button,state)
local x,y,z
if button == "left" and state == "up" then
x = 1959.55
-- get the text entered in the 'username' field
y = -1714.46
local username = guiGetText(edtUser)
z = 10
-- get the text entered in the 'password' field
spawnPlayer(source, x, y, z)
local password = guiGetText(edtPass)
fadeCamera(source, true)
 
outputChatBox("Welcome to My Server", source)
-- if the username and password both exist
if username and username ~= "" and password and password ~= "" then
-- trigger the server event 'submitLogin' and pass the username and password to it
triggerServerEvent("submitLogin", getRootElement(), username, password)
 
-- hide the gui, hide the cursor and return control to the player
guiSetInputEnabled(false)
guiSetVisible(wdwLogin, false)
showCursor(false)
else
-- otherwise, output a message to the player, do not trigger the server
-- and do not hide the gui
outputChatBox("Please enter a username and password.")
end
end
end
end
addEventHandler("onPlayerJoin", getRootElement(), joinHandler)
</syntaxhighlight>
</syntaxhighlight>
However, since we are going to spawn the player when the button is clicked, we must replace the "onPlayerJoin" event with the custom event triggered by the client script. Replace the above code with the following:
 
===Creating the serverside event===
At this point we now have all the code needed on the client-side, so open up your serverside 'script.lua' file (from the [[Scripting Introduction|Introduction to Scripting]]) or another suitable serverside file to work with.
 
On the server-side, recall that we are spawning the player as soon as they log in.
So, first of all, we will need to define the custom event that we used before on the client. This can be done using [[addEvent]] and [[addEventHandler]].
<syntaxhighlight lang="lua">
<syntaxhighlight lang="lua">
function joinHandler(username, password)
-- create our loginHandler function, with a username and password parameters (passed from the client GUI)
local x,y,z
function loginHandler(username,password)
x = 1959.55
 
y = -1714.46
z = 10
        if (client) then
      spawnPlayer(client, x, y, z)
      fadeCamera(client, true)
      outputChatBox("Welcome to My Server", client)
        end
end
end


addEvent("SubmitLogin", true)
-- define our custom event, and allow it to be triggered from the client ('true')
addEventHandler("SubmitLogin", getRootElement(), joinHandler)
addEvent("submitLogin",true)
-- add an event handler so that when submitLogin is triggered, the function loginHandler is called
addEventHandler("submitLogin",root,loginHandler)
</syntaxhighlight>
</syntaxhighlight>
Note that the second arguement of [[addEvent]] function (the one with value "true") specifies whether the event can be triggered by the other side, therefore we need to turn it on since the client is triggering it. Also note the variable "client", it's an internal variable used by MTA to identify the player who triggered the event.  
 
===Logging in===
Now we have a function that is called through the custom event 'submitLogin', we can start to work on logging in and spawning the player, using our 'loginHandler' function:
<syntaxhighlight lang="lua">
function loginHandler(username,password)
-- cancel if this was not triggered by a client
if not client then return end
-- check that the username and password are correct
if username == "user" and password == "apple" then
-- the player has successfully logged in, so spawn them
spawnPlayer(client, 1959.55, -1714.46, 10)
fadeCamera(client, true)
setCameraTarget(client, client)
outputChatBox("Welcome to My Server.", client)
else
-- if the username or password are not correct, output a message to the player
outputChatBox("Invalid username and password. Please re-connect and try again.", client)
end
end
addEvent("submitLogin",true)
addEventHandler("submitLogin",root,loginHandler)
</syntaxhighlight>
'''For the purposes of this tutorial, a very basic username and password system is shown. For a more comprehensive alternative, you can use the Account System or a MySQL database.'''
 
Also note the use of the variable "client", it's an internal variable used by MTA to identify the player who triggered the event.  
 


Finally, do not forget to include the new gui.lua file in the meta.xml of the main resource, and label it as a client script:
Finally, do not forget to include the new gui.lua file in the meta.xml of the main resource, and label it as a client script:
Line 151: Line 263:
</syntaxhighlight>
</syntaxhighlight>


As to this point, we have a basic login window that spawns the player when the "login" button is clicked. You can also use the username and password submitted by the [[triggerServerEvent]] function to verify the player's identify before spawning him.
If you do not want your client file not to be downloaded, set cache="false"
<syntaxhighlight lang="xml">
<script src="client/gui.lua" type="client" cache="false"/>
</syntaxhighlight>
 
At this point, we now have a basic login window that checks the player's username and password when the login button is clicked. If they are correct, the player is automatically spawned.
 
For further help with GUI, see the [[:Category:GUI_Tutorials|GUI tutorials]].


[[Category:GUI_Tutorials]]
[[hu:Introduction to Scripting the GUI]]
[[pl:Introduction to Scripting the GUI]]
[[it:Introduzione_allo_scripting_della_GUI]]
[[it:Introduzione_allo_scripting_della_GUI]]
[[ru:Introduction to Scripting the GUI]]
[[ru:Introduction to Scripting the GUI]]
[[es:Introducción a la Programación de GUI]]
[[zh-cn:脚本编写介绍 - 带有图形界面]]

Latest revision as of 17:19, 20 June 2024

One important feature in MTA:SA is the ability to script customized GUI (Graphic User Interface). The GUI consists of windows, buttons, edit boxes, checkboxes... Almost every standard form components in graphical environments. They can be displayed while the user is in-game, and used for inputs and outputs in place of traditional commands.

Admin Console GUI

A tutorial to make a login window

In this tutorial, we'll make a simple login window, with two input boxes and a button. The window appears when the player joins the game, and once the button is clicked, the player is spawned. The tutorial will continue the gamemode we made in Introduction to Scripting (If you have used the Introduction to Scripting, you will need to remove or comment the spawnPlayer line in the "joinHandler" function in your code, as we will be replacing it with a GUI alternative in this tutorial). We'll also take a look at client-side scripting.

Draw the window

All the GUI must be made client-side. It is also a good practice to keep all the client scripts in a separate folder.

Browse to /Your MTA Server/mods/deathmatch/resources/myserver/ directory, and create a folder named "client". Under /client/ directory, create a text file and name it "gui.lua".

In this file we will write a function that draws the window. To create a window we will use guiCreateWindow:

function createLoginWindow()
	-- define the X and Y positions of the window
	local X = 0.375
	local Y = 0.375
	-- define the width and height of the window
	local Width = 0.25
	local Height = 0.25
	-- create the window and save its element value into the variable 'wdwLogin'
	-- click on the function's name to read its documentation
	wdwLogin = guiCreateWindow(X, Y, Width, Height, "Please Log In", true)
end

Relative and Absolute

Note that the final argument passed to guiCreateWindow in the above example is true. This indicates that the coordinates and dimensions of the window are relative, meaning they are a percentage of the total screen size. This means that if the far left side of the screen is 0, and the far right is 1, an X position of 0.5 would represent the center point of the screen. Similarly, if the top of the screen is 0 and the bottom is 1, a Y position of 0.2 would be 20% of the way down the screen. The same principles apply to both Width and Height as well (with a Width value of 0.5 meaning the window will be half as wide as the screen).

The alternative to using relative values is using absolute (by passing false instead of true to guiCreateWindow). Absolute values are calculated as the total number of pixels from the top-left corner of the parent (if no GUI element parent is specified, the parent is the screen itself). If we assume a screen resolution of 1920x1200, the far left side of the screen being 0 pixels and the far-right being 1920 pixels, an X position of 960 will represent the center point of the screen. Similarly, if the top of the screen is 0 pixels and the bottom is 1200, a Y position of 20 would be 20 pixels down from the top of the screen. The same principles apply to both Width and Height as well (with a Width value of 50 meaning the window will be 50 pixels wide). You can use guiGetScreenSize and a little maths to calculate certain absolute positions.

The differences between using relative and absolute values are quite simple; GUI created using absolute values will always remain exactly the same pixel size and position, while GUI created using relative values will always be a percentage of its parent's size.

Absolute is generally easier to maintain when editing code by hand, however, your choice of type depends on the situation you are using it for.

For the purposes of this introduction, we will be using relative values.

Adding the components

Next, we'll add the text labels (saying "username:" and "password:"), edit boxes (for entering your data), and a button to log in.

To create buttons we use guiCreateButton and to create edit boxes use guiCreateEdit:

Note that we are now writing more code for our existing 'createLoginWindow' function. This is not a new function and is meant to replace what you already have.

function createLoginWindow()
	local X = 0.375
	local Y = 0.375
	local Width = 0.25
	local Height = 0.25
	wdwLogin = guiCreateWindow(X, Y, Width, Height, "Please Log In", true)
	
	-- define new X and Y positions for the first label
	X = 0.0825
	Y = 0.2
	-- define new Width and Height values for the first label
	Width = 0.25
	Height = 0.25
	-- create the first label, note the final argument passed is 'wdwLogin' meaning the window
	-- we created above is the parent of this label (so all the position and size values are now relative to the position of that window)
	guiCreateLabel(X, Y, Width, Height, "Username", true, wdwLogin)
	-- alter the Y value, so the second label is slightly below the first
	Y = 0.5
	guiCreateLabel(X, Y, Width, Height, "Password", true, wdwLogin)
	

	X = 0.415
	Y = 0.2
	Width = 0.5
	Height = 0.15
	edtUser = guiCreateEdit(X, Y, Width, Height, "", true, wdwLogin)
	Y = 0.5
	edtPass = guiCreateEdit(X, Y, Width, Height, "", true, wdwLogin)
	-- set the maximum character length for the username and password fields to 50
	guiEditSetMaxLength(edtUser, 50)
	guiEditSetMaxLength(edtPass, 50)
	
	X = 0.415
	Y = 0.7
	Width = 0.25
	Height = 0.2
	btnLogin = guiCreateButton(X, Y, Width, Height, "Log In", true, wdwLogin)
	
	-- make the window invisible
	guiSetVisible(wdwLogin, false)
end

Note that every GUI component created is a child of the window, this is done by specifying the parent element (wdwLogin, in this case) when creating the component.

This is very useful because not only does it mean that all the components are attached to the window and will move with it, but also that any changes done to the parent window will be applied down the tree to these child components. For example, we can now hide all of the GUI we just created by simply hiding the window:

guiSetVisible(wdwLogin, false) --hides all the GUI we made so we can show them to the player at the appropriate moment. 

Using the function we wrote

The createLoginWindow function is now complete, but it won't do anything until we call it. It is recommended to create all GUI when the client resource starts, hide them, and show them to the player later when needed. Therefore, we'll write an event handler for "onClientResourceStart" to create the window:

-- attach the event handler to the root element of the resource
-- this means it will only trigger when its own resource is started
addEventHandler("onClientResourceStart", getResourceRootElement(), 
	function ()
		createLoginWindow()
	end
)	

As this is a login window, we now need to show the window when the player joins the game. This can be done using the same event, "onClientResourceStart", so we can modify the above code to include showing the window:

Note that we are now writing more code for our existing 'onClientResourceStart' handler. This is not a new event handler and is meant to replace what you already have.

addEventHandler("onClientResourceStart", getResourceRootElement(), 
	function ()
		-- create the log in window and its components
		createLoginWindow()

		-- output a brief welcome message to the player
                outputChatBox("Welcome to My MTA:SA Server, please log in.")

		-- if the GUI was successfully created, then show the GUI to the player
	        if (wdwLogin ~= nil) then
			guiSetVisible(wdwLogin, true)
		else
			-- if the GUI hasn't been properly created, tell the player
			outputChatBox("An unexpected error has occurred and the login GUI has not been created.")
	        end 

		-- enable the player's cursor (so they can select and click on the components)
	        showCursor(true)
		-- set the input focus onto the GUI, allowing players (for example) to press 'T' without the chatbox opening
	        guiSetInputEnabled(true)
	end
)	

Note that we have a simple security check before making the window visible, so in the unlikely event that the window has not been created, meaning wdwLogin is not a valid element, we don't get an error and just inform the player what has happened. In the next step, we will create the button functionality for the login button.

Scripting the button

Now that we have created our GUI and shown it to the player, we need to make it work.

Detecting the click

When the player clicks on any part of the GUI, the event "onClientGUIClick" will be triggered for the GUI component you clicked on. This allows us to easily detect any clicks on the GUI elements we want to use. For example, we can attach the event to the btnLogin button to catch any clicks on it:

-- attach the event onClientGUIClick to btnLogin and set it to trigger the 'clientSubmitLogin' function
addEventHandler("onClientGUIClick", btnLogin, clientSubmitLogin, false)

Note the final argument passed is "false". This indicates that the event will only trigger directly on btnLogin, not if the event has propagated up or down the tree. Setting this to "true" while attaching to GUI elements will mean that clicking on any element in the same branch will trigger this event.

This line of code can now be added inside the createLoginWindow function. It is a common mistake to try and attach events to non-existent GUI elements, so make sure you always attach your events after the GUI element (in this case, the button) has been created:

Note that we are now writing more code for our existing 'createLoginWindow' function.

function createLoginWindow()
-- create all our GUI elements
...
-- now add our onClientGUIClick event to the button we just created
end
addEventHandler("onClientGUIClick", btnLogin, clientSubmitLogin, false)

Managing the click

Now that we can detect when the player clicks on the button, we need to write code to manage what happens when they do. In our onClientGUIClick event handle, we told it to call the function clientSubmitLogin whenever btnLogin is clicked. Therefore, we can now use the function clientSubmitLogin to control what happens when the button is clicked:

-- create the function and define the 'button' and 'state' parameters
-- (these are passed automatically by onClientGUIClick)
function clientSubmitLogin(button,state)
	-- if our login button was clicked with the left mouse button, and the state of the mouse button is up
	if button == "left" and state == "up" then
		-- move the input focus back onto the game (allowing players to move around, open the chatbox, etc)
		guiSetInputEnabled(false)
		-- hide the window and all the components
		guiSetVisible(wdwLogin, false)
		-- hide the mouse cursor
		showCursor(false)
	end
end

Now, when the button is clicked, the window will be hidden and all controls will be returned to the player. Next, we will tell the server to allow the player to spawn.

Triggering the server

Triggering the server can be done using triggerServerEvent. This allows you to trigger a specified event on the server from the client. The same can be done in reverse using triggerClientEvent. Here, we use the triggerServerEvent function to call our own custom event on the server, named "submitLogin", which will then control the spawning of the player serverside.

Note that we are now writing more code for our existing 'clientSubmitLogin' function. This is not a new function and is meant to replace what you already have.

function clientSubmitLogin(button,state)
	if button == "left" and state == "up" then
		-- get the text entered in the 'username' field
		local username = guiGetText(edtUser)
		-- get the text entered in the 'password' field
		local password = guiGetText(edtPass)

		-- if the username and password both exist
		if username and username ~= "" and password and password ~= "" then
			-- trigger the server event 'submitLogin' and pass the username and password to it
			triggerServerEvent("submitLogin", getRootElement(), username, password)

			-- hide the gui, hide the cursor and return control to the player
			guiSetInputEnabled(false)
			guiSetVisible(wdwLogin, false)
			showCursor(false)
		else
			-- otherwise, output a message to the player, do not trigger the server
			-- and do not hide the gui
			outputChatBox("Please enter a username and password.")
		end
	end
end

Creating the serverside event

At this point we now have all the code needed on the client-side, so open up your serverside 'script.lua' file (from the Introduction to Scripting) or another suitable serverside file to work with.

On the server-side, recall that we are spawning the player as soon as they log in. So, first of all, we will need to define the custom event that we used before on the client. This can be done using addEvent and addEventHandler.

-- create our loginHandler function, with a username and password parameters (passed from the client GUI)
function loginHandler(username,password)

end

-- define our custom event, and allow it to be triggered from the client ('true')
addEvent("submitLogin",true)
-- add an event handler so that when submitLogin is triggered, the function loginHandler is called
addEventHandler("submitLogin",root,loginHandler)

Logging in

Now we have a function that is called through the custom event 'submitLogin', we can start to work on logging in and spawning the player, using our 'loginHandler' function:

function loginHandler(username,password)
	-- cancel if this was not triggered by a client
	if not client then return end
	-- check that the username and password are correct
	if username == "user" and password == "apple" then
		-- the player has successfully logged in, so spawn them
		spawnPlayer(client, 1959.55, -1714.46, 10)
		fadeCamera(client, true)
		setCameraTarget(client, client)
		outputChatBox("Welcome to My Server.", client)
	else
		-- if the username or password are not correct, output a message to the player
		outputChatBox("Invalid username and password. Please re-connect and try again.", client)
	end			
end
addEvent("submitLogin",true)
addEventHandler("submitLogin",root,loginHandler)

For the purposes of this tutorial, a very basic username and password system is shown. For a more comprehensive alternative, you can use the Account System or a MySQL database.

Also note the use of the variable "client", it's an internal variable used by MTA to identify the player who triggered the event.


Finally, do not forget to include the new gui.lua file in the meta.xml of the main resource, and label it as a client script:

<script src="client/gui.lua" type="client" />

If you do not want your client file not to be downloaded, set cache="false"

<script src="client/gui.lua" type="client" cache="false"/>

At this point, we now have a basic login window that checks the player's username and password when the login button is clicked. If they are correct, the player is automatically spawned.

For further help with GUI, see the GUI tutorials.