VGUI Creating Custom Elements

<cat>Dev.UI</cat>
<title>VGUI Creating Custom Elements</title>


# Why Create Custom VGUI Elements?
Developing custom VGUI (Valve Graphical User Interface) elements offers numerous advantages, with enhanced code readability and maintainability standing out as primary benefits. These new elements do not always need to be entirely original components; in many cases, they are simple modifications or extensions of the game's base panels. By adopting this approach, you can streamline the development process, making UI elements much more manageable.

Imagine a project in which you typically employ a <page>DButton</page>. Instead of laboriously restyling and modifying each <page>DButton</page> separately, envision creating a new element that inherits all the functionalities of the <page>DButton</page>. This approach enables you to effortlessly restyle and enhance its capabilities in a single location.

Now you _can_ create multiple elements in the same file using <page>vgui.CreateFromTable</page>, however, you normally only want to do this for specifically **Internal** elements. Components that only exist to serve a larger Element within the same file. 

# The Main Steps to Creating a Custom Element

## The Pre-Knowledge
Before we start going into depth about what a panel is and how to create one let us first establish some base knowledge on how VGUI elements are loaded and located within your <page text="Addon Structure">Lua Folder Structure</page> and within the larger `garrysmod/` folders.

Assuming you have a basic grasp of the Garry's Mod filesystem, here's a crash course: all contents within your addon folder essentially get "merged" with the pre-existing folder structure in your game copy. Although no actual file relocation occurs, it's crucial to remeber that the engine interprets your `*myAddonName*/lua/autorun/client/example.lua` as residing in the same location as `garrysmod/lua/autorun/client/example.lua`.

This is emphasized because it is good practice to use this to our advantage when creating new elements. Looking at the <page text="Addon Structure">Lua Folder Structure</page> page we can see our addons can have a dedicated `lua/vgui` folder. This is where you should create and store your new vgui elements. The benefit to this is that your new elements will be loaded and registered just as if they were shipped with the default game. meaning we don't need to worry about load order.

Lastly there are a few things to note. Your new elements should be given distinct names as to not collide with potentially any other addons an end user might also have loaded. A good example of this is the games default panels all being prefixed with `D`. Your filenames should be just the name of your element. This does not affect the code directly by doing this you will thank yourself later. Lastly be wise with how you create elements, a Red and Blue button do not need to be their own components, make one button component and style both variants individually. 

## Step 1: All Elements Are Tables
At their core all vgui elements are just fancy tables. This means that the first step to creating any new element is to create the table that will define this element.

```lua
local PANEL = {}

```

Above we create a local empty table and called it `PANEL`. This name _can_ be anything you'd like but `PANEL` is the standard and its encouraged you also use it.



## Step 2: The Init Function
The Init function is always the first <page text="Panel Hook">PANEL_Hooks</page> called when a panel is created. This hook is only called once on creation so it is normally used to set default values and static values of the panel. This could range from inital values you want the panel to have to more dynamic functions like setting the <page>Panel:Dock</page> state.

```lua
function PANEL:Init()
	-- Default / Initial Values Set Here
end
```



## Step 3: The Paint Function
This function will determine the look of panel. This can be a bit unintuitive at first so please take the time to understand how the paint hook really works. Painting a panel is **NOT** persistent, every panel must be painted every single frame it is visible or it will not appear. This means **unlike** the `Init` function, this <page text="Panel Hook">PANEL_Hooks</page> is called every **Frame** the panel is visible. Now there are two libraries dedicated to painting panels, first is the <page>surface</page> library. This is the go-to library you want to use. Secondly there is the <page>draw</page> library. The <page>draw</page> library is just a wrapper for the <page>surface</page> library making some of the more difficult things to do in <page>surface</page> easier. Most Notably the <page>draw.RoundedBox</page>

The <page text="Paint Hook">PANEL:Paint</page> is always called with two arguments; the width and the height of the panel (sometimes denoted as `w` and `h`) this allows you to easily access the panels width and height in this hook to use within your <page>surface</page> and <page>draw</page> functions

```lua
function PANEL:Paint( width, height )
	--Surface and Draw functions go here

	surface.SetDrawColor(255,0,0,255)
	surface.DrawRect( 0, 0, width, height ) -- Using surface to draw a standard rectangle
	
	draw.RoundedBox( 15, 0, 0, width, height, Color(0,255,0,255))  -- Using Draw to draw a rounded green box

end

```

Above include very primitive examples from both the <page>surface</page> and <page>draw</page> libraries. Now Order of these functions matter within in the <page text="Paint Hook">PANEL:Paint</page>. If you were to copy and paste this paint function ontop an existing panel it would look something like:
<image src="aaf9e/8dc4174650c9356.png" size="565" name="sqre.png" />
Why? Because look at the order we called our painting functions, First we drew the red rectangle AND THEN drew the Green rounded rectangle. This means that our green rounded rectangle was painted OVER the red rectangle we initially drew with <page>surface</page>

We cant cover everything relating to painting panels here but the biggest things to keep in mind is that: You can only paint within the actual bounds of the panel unless you use <page>PANEL:NoClipping</page> or <page>Global.DisableClipping</page>. and that the order in which you paint matters, see the red rectangle and green rounded box above.


## Step 4: Registering Your New Element
Registering your element should always be the last thing you do in the elements file (unless creating internal elements, then register after each internal element is done). Once your ready to register your element you will need to call the <page>vgui.Register</page> function. This function is how you will define your elements name, the name of created table we used (PANEL), and the optional name of a base panel we want derive this element from.

```lua
vgui.Register( "WikiExample", PANEL, "Panel")

```

above is an example of a completed <page>vgui.Register</page> function.


# Using Your New Element
once you have registered your new custom element with <page>vgui.Register</page> in step 4 your now able to create that element within your main project files using the name you registered with it

```lua
local MyNewElement = vgui.Create( "WikiExample" )
```



# Additional Information 

## Inheritance
Inheritance is important when working with Garry mod UI. Garry's Mod default panels already come with a lot of built in functionalities that you can leverage when creating your own panel. Its worth looking through the <page>VGUI Element List</page> to see if your able to derive your new panel from one of them and save yourself some time.

Another part of that is knowing where functions come from. a popular misconception is "I need to derive my panel from a <page>DButton</page> in order to have access to `DoClick()`" when in actuality when you look at <page text="Where that function comes from">DLabel:DoClick</page> you really only need to derive your panel from a <page>DLabel</page> to have access to `DoClick()`

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