Custom UI Development

Hytale features a sophisticated UI system that allows plugins to create custom interfaces, pages, windows, and HUD elements. The UI is built dynamically on the server and sent to the client.

Overview

The UI system consists of several components:

Component	Purpose
Pages	Full-screen or overlay UI (menus, dialogs)
Windows	Inventory/container-style interfaces
HUD	Persistent on-screen elements
.ui Files	Reusable BSON layout templates

UI Architecture


Server Plugin                    Client
     │                              │
     │  CustomPage Packet           │
     ├─────────────────────────────▶│
     │  (BSON commands + events)    │
     │                              │
     │  CustomPageEvent Packet      │
     │◀─────────────────────────────┤
     │  (user interactions)         │
     │                              │

Creating Custom Pages

Basic Custom Page

For simple, non-interactive pages:


public class WelcomePage extends BasicCustomUIPage {
 
    public WelcomePage(PlayerRef playerRef) {
        super(playerRef, CustomPageLifetime.CanDismiss);
    }
 
    @Override
    public void build(UICommandBuilder builder) {
        // Load a .ui layout file
        builder.append("Pages/WelcomePage.ui");
 
        // Set text values
        builder.set("#Title.Text", "Welcome to the Server!");
        builder.set("#Subtitle.Text", "Press ESC to close");
    }
}

Interactive Custom Page

For pages that handle user input:


public class TeamSelectPage extends InteractiveCustomUIPage<TeamSelectEventData> {
 
    public TeamSelectPage(PlayerRef playerRef) {
        super(playerRef, CustomPageLifetime.CanDismiss, TeamSelectEventData.CODEC);
    }
 
    @Override
    public void build(Ref<EntityStore> ref, UICommandBuilder builder,
                     UIEventBuilder eventBuilder, Store<EntityStore> store) {
        builder.append("Pages/TeamSelect.ui");
 
        // Add button click handlers
        eventBuilder.addEventBinding(
            CustomUIEventBindingType.Activating,
            "#RedTeamButton",
            EventData.of("Team", "red")
        );
 
        eventBuilder.addEventBinding(
            CustomUIEventBindingType.Activating,
            "#BlueTeamButton",
            EventData.of("Team", "blue")
        );
    }
 
    @Override
    public void handleDataEvent(Ref<EntityStore> ref, Store<EntityStore> store,
                               TeamSelectEventData data) {
        Player player = store.getComponent(ref, Player.getComponentType());
 
        if ("red".equals(data.team)) {
            player.sendMessage(Message.raw("You joined Red Team!"));
        } else if ("blue".equals(data.team)) {
            player.sendMessage(Message.raw("You joined Blue Team!"));
        }
 
        // Close the page
        player.getPageManager().setPage(ref, store, Page.None);
    }
 
    // Event data class with codec
    public static class TeamSelectEventData {
        public String team;
 
        public static final BuilderCodec<TeamSelectEventData> CODEC =
            BuilderCodec.builder(TeamSelectEventData.class, TeamSelectEventData::new)
                .withField("Team", String.class, d -> d.team, (d, v) -> d.team = v)
                .build();
    }
}

Opening a Page


// In your plugin or command
Player player = // get player
PlayerRef playerRef = player.getPlayerRef();
 
CustomUIPage page = new TeamSelectPage(playerRef);
player.getPageManager().openCustomPage(ref, store, page);

Page Lifetime

The CustomPageLifetime enum controls how players can close pages:

Lifetime	Description
`CantClose`	Player cannot close (forced UI)
`CanDismiss`	Player can press ESC to close
`CanDismissOrCloseThroughInteraction`	Close via ESC or interaction


// Force player to interact with the page
super(playerRef, CustomPageLifetime.CantClose, eventCodec);
 
// Allow ESC to close
super(playerRef, CustomPageLifetime.CanDismiss, eventCodec);

UICommandBuilder API

The UICommandBuilder sends UI commands to the client:

Loading Layouts


// Load a .ui file as root
builder.append("Pages/MyPage.ui");
 
// Append to a container
builder.append("#ItemList", "Components/ItemSlot.ui");
 
// Insert before an element
builder.insertBefore("#Footer", "Components/Separator.ui");

Setting Values


// Set text
builder.set("#Title.Text", "Hello World");
builder.set("#Description.Text", Message.translation("my.translation.key"));
 
// Set numbers
builder.set("#HealthBar.Value", 0.75f);
builder.set("#Counter.Text", String.valueOf(count));
 
// Set items
builder.set("#ItemSlot.ItemId", itemStack);
 
// Set visibility
builder.set("#ErrorMessage.Visible", hasError);
 
// Set colors (as string values)
builder.set("#StatusText.Color", "#FF0000");

Managing Elements


// Clear children of a container
builder.clear("#ItemContainer");
 
// Remove an element
builder.remove("#OldElement");

Dynamic Lists


// Build a list of items
builder.clear("#ItemList");
 
for (int i = 0; i < items.size(); i++) {
    String selector = "#ItemList[" + i + "]";
 
    // Add item slot
    builder.append("#ItemList", "Components/ItemSlot.ui");
 
    // Set item data
    builder.set(selector + " #Icon.ItemId", items.get(i).getItemId());
    builder.set(selector + " #Name.Text", items.get(i).getName());
    builder.set(selector + " #Count.Text", String.valueOf(items.get(i).getQuantity()));
}

UIEventBuilder API

The UIEventBuilder binds client events to server handlers:

Event Types

Event Type	Description
`Activating`	Button click / element activated
`RightClicking`	Right-click on element
`DoubleClicking`	Double-click
`MouseEntered`	Mouse hover start
`MouseExited`	Mouse hover end
`ValueChanged`	Input/slider value changed
`FocusGained`	Element gained focus
`FocusLost`	Element lost focus
`KeyDown`	Key pressed
`SelectedTabChanged`	Tab selection changed
`SlotClicking`	Inventory slot clicked
`Dropped`	Item dropped

Basic Event Binding


// Simple click handler
eventBuilder.addEventBinding(
    CustomUIEventBindingType.Activating,
    "#MyButton"
);
 
// Click with data
eventBuilder.addEventBinding(
    CustomUIEventBindingType.Activating,
    "#DeleteButton",
    EventData.of("Action", "delete").append("ItemId", itemId)
);

Input Events


// Text input change
eventBuilder.addEventBinding(
    CustomUIEventBindingType.ValueChanged,
    "#SearchInput",
    EventData.of("@SearchQuery", "#SearchInput.Value"),
    false  // Don't lock interface
);
 
// Slider change
eventBuilder.addEventBinding(
    CustomUIEventBindingType.ValueChanged,
    "#VolumeSlider",
    EventData.of("@Volume", "#VolumeSlider.Value"),
    false
);

Event Data References

Use @ prefix to reference UI element values:


EventData.of("@SearchQuery", "#SearchInput.Value")  // Gets input text
EventData.of("@SliderValue", "#Slider.Value")       // Gets slider value
EventData.of("@SelectedTab", "#TabBar.SelectedIndex") // Gets selected tab

Updating Pages Dynamically

Send incremental updates without rebuilding the entire page:


@Override
public void handleDataEvent(Ref<EntityStore> ref, Store<EntityStore> store,
                           MyEventData data) {
    if (data.searchQuery != null) {
        // Build update
        UICommandBuilder builder = new UICommandBuilder();
        UIEventBuilder eventBuilder = new UIEventBuilder();
 
        // Update only the search results
        buildSearchResults(builder, eventBuilder, data.searchQuery);
 
        // Send partial update (false = don't clear)
        sendUpdate(builder, eventBuilder, false);
    }
}

Windows (Inventory UI)

Windows are used for inventory and container interfaces:


public class CustomChestWindow extends ItemContainerWindow {
 
    public CustomChestWindow(ItemContainer container) {
        super(WindowType.Chest, container);
    }
 
    @Override
    public void init(PlayerRef playerRef, WindowManager manager) {
        super.init(playerRef, manager);
    }
 
    @Override
    public void handleAction(Ref<EntityStore> ref, Store<EntityStore> store,
                            WindowAction action) {
        // Handle item moves, clicks, etc.
    }
}

Opening Windows


Player player = // get player
Window window = new CustomChestWindow(container);
player.getWindowManager().openWindow(window);
 
// Open with a page
player.getPageManager().openCustomPageWithWindows(
    ref, store, myPage, window1, window2
);

HUD Elements

Create custom HUD overlays:


public class CustomHud extends CustomUIHud {
 
    @Override
    public void build(UICommandBuilder builder) {
        builder.append("HUD/CustomOverlay.ui");
        builder.set("#ScoreText.Text", "Score: 0");
    }
 
    public void updateScore(int score) {
        UICommandBuilder builder = new UICommandBuilder();
        builder.set("#ScoreText.Text", "Score: " + score);
        update(false, builder);  // Send update
    }
}

Managing HUD


Player player = // get player
HudManager hudManager = player.getHudManager();
 
// Set custom HUD
CustomHud customHud = new CustomHud();
hudManager.setCustomHud(playerRef, customHud);
 
// Show/hide default HUD components
hudManager.hideHudComponents(playerRef, HudComponent.Compass);
hudManager.showHudComponents(playerRef, HudComponent.Health, HudComponent.Stamina);
 
// Reset to default
hudManager.resetHud(playerRef);

Default HUD Components

Available HudComponent values:

Health, Mana, Stamina, Oxygen
Hotbar, Reticle, Compass
Chat, Notifications, KillFeed
ObjectivePanel, PortalPanel
StatusIcons, InputBindings
Speedometer, AmmoIndicator
And more…

UI Technology

Based on Discord discussions and code analysis, Hytale’s UI system uses NoesisGUI, an industry-standard C++ UI framework:

“NoesisGUI: C++ Game UI Framework… It has a C# SDK but it’s an industry standard UI framework” - Discord community

NoesisGUI Features:

XAML-based UI definitions
GPU-accelerated rendering
C# SDK integration (client-side)
Server sends UI commands via BSON

This explains why UI files use BSON documents - the server describes the UI declaratively, and the NoesisGUI client renders it.

.ui File Format

UI layouts are BSON documents. The exact format is not fully documented, but based on decompiled code:

File Structure


assets/
└── myplugin/
    └── ui/
        ├── Pages/
        │   └── MyPage.ui
        └── Components/
            └── ItemSlot.ui

Element Selectors


"#ElementId"                    // By ID
"#Container[0]"                 // First child
"#Container[0] #Child"          // Nested element
"#Element.Property"             // Element property

Using References


// Reference a value from another .ui file
Value<String> style = Value.ref("Common/Styles.ui", "ButtonStyle");
builder.set("#MyButton.Style", style);

Community Notes

From Discord discussions about custom UI:

“We won’t be creating chest UIs in Hytale, so it will make sense we will be using a real language to define UI for players” - Community insight

“Imagine an actual screen to join a game or selecting teams, created by designers” - On the flexibility of the system

“The server will probably send JSON data describing the UI and callback events for things like clicking on buttons” - Technical speculation (confirmed by decompiled code showing BSON commands)

Known Limitations

Based on Discord community feedback, be aware of these limitations:

CustomUIHud Limitations

“Hey were you able to make an uninteractable hud at all? Been trying unsuccesfully” - Discord

One Custom HUD Per Player Per Plugin: You can only have one CustomUIHud active per player at a time. Multiple plugins can have their own HUDs.
HUD Makes Player Static: When a custom HUD is shown via certain methods, the player may become unable to move until they press ESC.

File Path Format: Don’t include “Hud/” prefix if your file is already in the Hud folder:


// WRONG - If file is at assets/myplugin/ui/Hud/myui.ui
builder.append("Hud/myui.ui");  // Might cause "could not find document" error
 
// CORRECT
builder.append("myui.ui");

Hot Reload Not Supported: Custom UI changes require a full server restart. The UI files are loaded at startup.

“Custom UI requires page popups (restricts interactivity)” - Discord

Custom UI pages are modal popups, not inline overlays
Players must dismiss the page to continue playing
For always-visible UI, use CustomUIHud instead

Cannot Extend Existing UI

You cannot modify or extend the built-in inventory UI
Cannot add custom slots to the vanilla inventory
Must create entirely custom pages/windows for custom inventory features

Server Restart Required

“Not gonna work here when you need to rebuild custom UI elements server needs full restart to load new ones” - Discord

UI file changes are not hot-reloadable. After modifying .ui files:

Stop the server
Rebuild your plugin JAR
Replace the JAR in the mods folder
Start the server

Known Issues (Early Access)

Community members developing UI-heavy plugins have reported:

“The UI is invisible even with AlwaysOn: true” - UI rendering issues being investigated

“Says could not find document Hud/myui.ui for custom ui append command” - File path issues

“JAR Structure: Verified. manifest.json is at root, and assets/myplugin/interfaces.json + assets/myplugin/ui/my_ui.json are present” - Asset pack structure requirements

Asset Pack Integration

If your plugin includes custom .ui files, set IncludesAssetPack: true in manifest.json:


{
  "Group": "com.example",
  "Name": "MyUIPlugin",
  "IncludesAssetPack": true,
  "Main": "com.example.MyPlugin"
}

Complete Example

Here’s a full example of a shop page:


public class ShopPage extends InteractiveCustomUIPage<ShopPageEventData> {
 
    private final List<ShopItem> items;
 
    public ShopPage(PlayerRef playerRef, List<ShopItem> items) {
        super(playerRef, CustomPageLifetime.CanDismiss, ShopPageEventData.CODEC);
        this.items = items;
    }
 
    @Override
    public void build(Ref<EntityStore> ref, UICommandBuilder builder,
                     UIEventBuilder eventBuilder, Store<EntityStore> store) {
 
        // Load main layout
        builder.append("Pages/ShopPage.ui");
        builder.set("#Title.Text", "Server Shop");
 
        // Clear and build item list
        builder.clear("#ItemGrid");
 
        for (int i = 0; i < items.size(); i++) {
            ShopItem item = items.get(i);
            String selector = "#ItemGrid[" + i + "]";
 
            // Add item slot
            builder.append("#ItemGrid", "Components/ShopSlot.ui");
 
            // Set item details
            builder.set(selector + " #Icon.ItemId", item.getItemId());
            builder.set(selector + " #Name.Text", item.getName());
            builder.set(selector + " #Price.Text", "$" + item.getPrice());
 
            // Add buy button event
            eventBuilder.addEventBinding(
                CustomUIEventBindingType.Activating,
                selector + " #BuyButton",
                EventData.of("Action", "buy").append("ItemIndex", String.valueOf(i))
            );
        }
 
        // Close button
        eventBuilder.addEventBinding(
            CustomUIEventBindingType.Activating,
            "#CloseButton"
        );
    }
 
    @Override
    public void handleDataEvent(Ref<EntityStore> ref, Store<EntityStore> store,
                               ShopPageEventData data) {
        Player player = store.getComponent(ref, Player.getComponentType());
 
        if ("buy".equals(data.action) && data.itemIndex != null) {
            int index = Integer.parseInt(data.itemIndex);
            ShopItem item = items.get(index);
 
            // Process purchase...
            player.sendMessage(Message.raw("You bought " + item.getName()));
        }
 
        // If no action, close was clicked
        if (data.action == null) {
            player.getPageManager().setPage(ref, store, Page.None);
        }
    }
 
    public static class ShopPageEventData {
        public String action;
        public String itemIndex;
 
        public static final BuilderCodec<ShopPageEventData> CODEC =
            BuilderCodec.builder(ShopPageEventData.class, ShopPageEventData::new)
                .withField("Action", String.class, d -> d.action, (d, v) -> d.action = v)
                .withField("ItemIndex", String.class, d -> d.itemIndex, (d, v) -> d.itemIndex = v)
                .build();
    }
}

Next Steps

Event System - Handle player events
ECS Architecture - Work with components
Complete Examples - Full plugin implementations