vide/docs/tut/crash-course.md

Vide Crash Course

Hello! This is a brief tutorial designed to give you a quick runthrough of the usage of Vide.

Vide is inspired by the popular libraries Vue and Fusion.

• Note that this tutorial assumes that you are familiar with Luau and the Roblox UI system.

Creating UI Instances

In Vide, it is intended to create all UI instances through code.

Instances are created using vide.create.

local vide = require(...)
local create = vide.create

local frame = create("Frame") {
    Name = "Background",
    Position = UDim2.fromScale(0.5, 0.5)
}

The function returns a constructor for a given class which then takes a table of properties to assign to create a new instance for that class.

Sometimes you want to do more than setting properties, such as setting children or connecting to events. Vide uses special keys called symbols which provide unique functionality like the above mentioned.

Children can be assigned to instances using the Children symbol.

local Children = vide.Children

local screenGui = create("ScreenGui") {
    Parent = game.StarterGui,

    [Children] = create("Frame") {
        AnchorPoint = Vector2.new(0.5, 0.5),
        Position = UDim2.fromScale(0.5, 0.5),
        Size = UDim2.fromScale(0.4, 0.7),

        [Children] = {
            create("TextLabel") {
                Text = "Hi"
            },

            create("TextLabel") {
                Text = "Bye"
            }
        }
    }
}

Here, we import the symbol vide.Children.

This symbol can accept an instance, an array of instances and nested arrays of instances. All given instances will be parented to the instance the symbol was used on.

Connecting To Events

Built-in instance events and property changed events can be connected to using two other symbols, vide.Event and vide.Changed.

local Event = vide.Event
local Changed = vide.Changed

local textBox = create("TextBox") {
    PlaceholderText = "Enter text",
    
    [Event.Focused] = function(...)
        print("User is focusing on text box")   
    end,

    [Changed.Text] = function(newText)
        print("New text: " .. newText)
    end
}

Both of these symbols can be indexed into to get a specific symbol for an event to connect to. The callback function for Event receives any event-specific arguments and the callback function for Changed receives the new property value as the only argument (unlike Instance:GetPropertyChangedSignal()).

State

State is the condition something is in at a specific time. The state of a program is simply the data it contains at some timepoint.

The purpose of all UI is to take some state and reflect that state visually.

In Vide, UI state is represented using special objects simply called state.

A state object in Vide can be created using vide.wrap.

local wrap = vide.wrap

local isVisible = wrap(false)

local image = create("ImageLabel") {
    Image = "rbxassetid://xxx",
    Visible = isVisible
}

while true do
    wait(1)
    isVisible.Value = not isVisible.Value
end

The function wrap will wrap any given value with a state object of type State<T> which can be read from/wrote to through its .value property.

In the above code, the ImageLabel.Visible property is assigned a state. Now any time that state's value is assigned to, ImageLabel.Visible will also update with the new value assigned, without you having to explicitly set the property. The above code gives the effect of the image label toggling visibility at a 1 second interval forever.

There are a few reasons why we use state objects instead of plain variables:

1. Vide detects when you assign a state object as a property value. This is known as binding and doing so will cause the property to automatically update whenever that state object's value is changed.
2. We can create new state objects that derive from other state objects, which again, automatically update when the derived state objects change.

The reason why this is useful, is that you as the programmer do not have to worry about manually updating variables or UI instances, you can just focus on defining how the data maps to UI and everything will automatically update when changes occur.

Derived State

You can create new state from other states. This is known as deriving state.

local derive = vide.derive

local count = wrap(0)

local text = derive(function(from)
    return "Count: " .. from(count)
end)

print(text.value) -- "Count: 0"

count.value += 1

print(text.value) -- "Count: 1"

Here we use vide.derive to derive a new state text which depends on count.

A function is used to transform the value of count, where the value returned becomes the new value of text. The function receives an argument named from which is used to capture dependent states. This is used to link count to text, so that whenever count is updated, text will be too.

Whenever count's value is changed, text will recompute its value and update anything dependent on text, such as UI.

States can be derived in a more concise manner when doing single operations such as concatenation:

local text = "Count: " .. count

You can derive new states using any Luau operator in this manner.

Components

Components in UI are just custom-made reusable pieces of UI made from other pieces of UI.

The recommended way to create components is to use functions that take a table of properties as an argument and return the new UI instance.

local function Background(args)
    return create("Frame") {
        BackgroundColor3 = Color3.new(0, 0, 0),
        Position = args.Position,
        Size = args.Size
    }
end

local background = Background {
    Position = UDim2.new(),
    Size = UDim2.new()
}

Above is a simple example of a frame component with its background color set to black.

A single parameter args is used to pass properties to the component.

Components allow you to encapsulate behavior. You can only modify the component in ways that are defined in the component. Looking at the above example, the only properties you are allowed to modify is Position and Size. This is a good approach to use for organised code.

However, properties concering layout (positional and size properties) aren't usually intrinsinc to the component. In most cases the user would want to be able to pass these properties without having to manually pass each one in the component.

For these cases, the vide.Layout symbol can be used.

local Layout = vide.Layout

local function Background(props)
    return create("Frame") {
        BackgroundColor3 = Color3.new(0, 0, 0),
        [Layout] = props[Layout],
        [Children] = props[Children]
    }
end

local background = Background {
    [Layout] = {
        AnchorPoint = Vector2.new(),
        Position = UDim2.new(),
        Size = UDim2.new(),
    },

    [Children] = {
        create("TextLabel") {},
        create("ImageLabel") {}
    }
}

Here, the Layout symbol automatically assigns those layout-specific properties without having to explicitly assign each one in the component definition. This is a very common case and for this reason it is recommended to only assign layout properties using the Layout symbol for consistency when dealing with components.

This allows you to pass through layout properties without breaking encapsulation.

Additionally, the above example shows how children can be passed to components in a similar manner.

Stateful components

Often, you need components that maintain their own internal state, such as a toggle button or a counter.

Below you can see how a simple counter component can be implemented.

local function Counter(args)
    -- create internal state unique to each component instance
    local count = wrap(0)

    return create("TextButton") {
        Name = "Counter",

        Text = "Count: " .. count

        [Event.Activated] = function()
            count.value += 1
        end

        [Layout] = args[Layout]
    }
end

create "ScreenGui" {
    Parent = game.StarterGui,

    [Children] = {
        Counter {
            [Layout] = {
                AnchorPoint = Vector2.new(0.5, 0),
                Position = UDim2.fromScale(0.5, 0),
                Size = UDim2.fromScale(0.3, 0.1)
            }
        }
    }
}

Here a reusable counter component is created, that when clicked on will increase its count and display it independent from other counter instances.

Tables of data

basic inventory

type Item = {
    Name: string,
    Icon: number    
}

local items = wrap({} :: Array<Item>)

local function ItemSlot(args)
    return create("Frame") {
        [Layout] = args[Layout]

        [Children] = {
            create("TextLabel") {
                Name = args.Name,
                [Layout] = ...
            },

            create("ImageLabel") {
                Image = "rbxassetid://" .. args.Icon,
                [Layout] = ...
            }
        }
    }
end

local function Inventory(args)
    return create("Frame") {
        [Layout] = args[Layout],

        [Children] = {
            create("UIListLayout") {},

            map(items, function(i, item)
                return ItemSlot {
                    Name = item.Name,
                    Icon = item.Icon,
                    [Layout] = { LayoutOrder = i, ... }
                }
            end)
        }
    }
end



More comprehensive tutorials are in the works. To find out more refer to the [`API documentation`](../../README#API).