lib-core.panel

Generic overlay-panel framework. v0.2.0 supports multiple panels open at the same time with 11 named layout-slot templates + custom-fn hook for bespoke positioning. Handles input dispatch (mouse click + wheel, edge-detected with reverse-open-order hit-test), renders titled panel overlays, and supports a context-menu layer on top. Designed as the glue layer between game modules and the engine render/input surfaces.

The single-active model from v0.1.1 is preserved as a backward- compatibility shim — panel.open(id), panel.close(), panel.is_open() without an id-arg keep their old semantics.

Version: 0.2.0 Lib-ID: lib-core.panel Requires: engine.render., engine.input., lib-core.input (lazy, for default-trigger) Tags: panel, overlay, ui, input, context-menu

Topology

graph LR
  this["lib-core.panel"]
  engine_render["engine.render.*"]
  engine_input["engine.input.*"]
  lib_core_input["lib-core.input"]
  this --> engine_render
  this --> engine_input
  this -.->|lazy| lib_core_input

Scope (v0.2.0)

v0.2.0 ships multi-active panels with layout-slot positioning, preserving full backward-compatibility with v0.1.1's single-active callers via shim semantics. The lib is the generic UI-Framework substrate — domain-free per ADR-0001/ADR-0049, consumed by Display- Libs (inventory-list-display, crafting-display, notify-display) and modules (vagrant-skeleton).

Supported (v0.2.0)

• Multi-active panels: multiple windows open simultaneously, each rendered + hit-tested independently.
• 11 layout-slot templates (center, left, right, top, bottom, four corners, left-half, right-half) for common positioning.
• Custom layout-fn hook function(sw, sh) -> {x,y,w,h} for bespoke positioning (HUD elements, status displays, custom tool UIs).
• Bw-Compat-Shim: v0.1.1 register(id, widget) ohne opts works unchanged; close()/is_open() ohne arg map to focused = last- opened.
• Theme system: shared theme via set_theme/get_theme (unchanged).
• Context-menu via show_context_menu (unchanged).
• Default-trigger key-binding via bind_default_trigger (unchanged).

Deferred (v0.3.0+)

• Z-order tiers (hud / normal / top) for layered rendering.
• Persistent windows (always-open, exempt from ESC-close).
• Input-block modes (none/self/all) for pass-through vs modal capture.
• Map-editor-style multi-region UI as first-class persistent widgets.

Deferred (v0.4.0+)

• Click-to-focus and explicit focus()/raise()/lower() API.
• Drag-by-title-bar (draggable opt).
• Resize-by-corner (resizable opt).
• min/max-size constraints + screen-clamp.

Deferred (post-v0.4.0)

• Window-decoration themes (per-window title-bar styles).
• Touch/mobile input adaptation.
• Window animations (slide-in, fade-in).
• Window groups / tabbed-windows / MDI parent-child hierarchies.
• Save/load of window-bounds across sessions.

API

panel.register(widget_id, widget_def, opts?)

Syntax: panel.register(widget_id: string, widget_def: table, opts?: table) -> void

opts is optional. Accepted keys: layout (slot-name string or function(sw, sh) -> {x,y,w,h}; defaults to "center") and z_tier ("normal"; v0.2.0 only the normal tier is exposed). See the Multi-Active + Layout-Slots section below for the full slot table.

Example:

panel.register("inventory", {
    title        = "Inventory",
    pause_on_open = true,
    render       = function(ctx)
        -- ctx.bounds = {x, y, w, h}; ctx.theme; ctx.is_focused
        engine.render.draw_text("(empty)", ctx.bounds.x, ctx.bounds.y,
                                ctx.theme.font_size_body, ctx.theme.text_color)
    end,
    handle_input = function(ctx, event)
        -- event.kind = "click"|"wheel"
        -- event.x, event.y, event.button (click only)
        -- event.dy (wheel only)
    end,
})

Registers a widget in the panel registry. widget_def.render and widget_def.handle_input must be functions; widget_def.title must be a string. Loud-error on duplicate widget_id or missing required fields.

---

panel.unregister(widget_id)

Syntax: panel.unregister(widget_id: string) -> void

Removes the widget from the registry. If the widget is currently open, closes it first (removes from open_order; clears any open context-menu if it was the last open window).

---

panel.open(widget_id)

Syntax: panel.open(widget_id: string) -> void

Opens widget_id. The window is pushed onto the top of open_order (becomes focused). Other open windows remain open. If widget_id is already open, it is brought to the front (re-focused). Loud-error if widget_id has not been registered.

v0.2.0 change: open(id) no longer closes other open panels. Multiple panels can be visible simultaneously. See §Bw-Compat Guarantee below for the migration recipe.

---

panel.close(widget_id?)

Syntax: panel.close(widget_id?: string) -> void

With widget_id: closes that specific window. Without arg (v0.1.1 bw-compat): closes the focused (last-opened) window. Clears any open context-menu when the last open window is closed.

---

panel.toggle(widget_id)

Syntax: panel.toggle(widget_id: string) -> void

If widget_id is currently open, closes it. Otherwise opens it. Handy for key-binding toggle semantics without manual state tracking.

---

panel.is_open(widget_id?)

Syntax: panel.is_open(widget_id?: string) -> bool

With widget_id: returns true iff that specific window is currently open. Without arg (v0.1.1 bw-compat): returns true if ANY window is open.

---

panel.is_pausing()

Syntax: panel.is_pausing() -> bool

Returns true if ANY currently-open window has pause_on_open = true. Modules can use this to gate their update loop (skip physics/AI while a pausing panel is open).

---

panel.set_theme(overrides)

Syntax: panel.set_theme(overrides: table) -> void

Example:

panel.set_theme({
    bg_color   = 0x101010F8,
    padding    = 12,
    font_size_body = 16,
})

Merges overrides into the active theme. Only keys declared in DEFAULT_THEME are accepted (capability-by-declaration). Loud-error on any unknown key with message "panel.set_theme: unknown theme key '<k>'".

---

panel.get_theme()

Syntax: panel.get_theme() -> table

Returns a shallow copy of the current merged theme. Safe to store; does not alias internal state.

---

panel.bind_default_trigger(key, widget_id)

Syntax: panel.bind_default_trigger(key: string|nil, widget_id: string) -> void

Example:

panel.register("inventory", { ... })
panel.bind_default_trigger("tab", "inventory")
-- or: panel.bind_default_trigger(nil, "inventory")  -- defaults to "tab"

Binds a keyboard key as the default toggle trigger for widget_id. key defaults to "tab" when nil. Lazy-requires lib-core.input to avoid module-load-time cycles. Loud-error if widget_id is not registered.

---

panel.update(dt)

Syntax: panel.update(dt: number) -> void

Must be called each game-update frame. Checks the default trigger key, reads mouse state, emits edge-detected click events (left and right independently), and dispatches wheel events. No-ops if no panels are open (but still tracks mouse state to avoid spurious edges on next open).

---

panel.render()

Syntax: panel.render() -> void

Must be called each render frame (inside the engine render phase). Draws the panel background, border, and title, then invokes widget_def.render(ctx). If a context-menu is open, renders it on top. No-op if no panels are open.

---

panel.show_context_menu(x, y, actions)

Syntax: panel.show_context_menu(x: number, y: number, actions: table) -> void

Example:

panel.show_context_menu(event.x, event.y, {
    { label = "Use",  callback = function(info) use_item()  end },
    { label = "Drop", callback = function(info) drop_item() end },
})

Pops up a context-menu at (x, y). actions must be a non-empty array of {label: string, callback: function} tables. Auto-repositions to remain within the screen boundary. The callback receives {close_menu: function} (which is a no-op in v0.1 since the menu closes itself before invoking the callback). Click outside any row auto-closes the menu.

---

panel._dispatch_event_for_test(event) — for tests only

Syntax: panel._dispatch_event_for_test(event: table) -> void

Direct passthrough to the internal _dispatch_event function. Allows test-modules to simulate input events without a running game loop (since M.update is not exercised headless).

---

v0.2.0 — Multi-Active + Layout-Slots

Multiple panels can now be open at the same time. The previous single-active model is preserved as the default for v0.1.1 callers via a backward-compatibility shim.

Layout-Slots

panel.register(id, widget_def, {layout = ...}) accepts:

• nil → "center" default.
• One of the 11 named templates (see table below).
• A custom function function(sw, sh) -> {x, y, w, h} for bespoke positioning (HP-bar, status-display, etc.).

Slot	x	y	w	h
"center" (default)	25% sw	20% sh	50% sw	60% sh
"left"	0	0	40% sw	sh
"right"	60% sw	0	40% sw	sh
"top"	0	0	sw	30% sh
"bottom"	0	70% sh	sw	30% sh
"top-left"	0	0	40% sw	50% sh
"top-right"	60% sw	0	40% sw	50% sh
"bottom-left"	0	50% sh	40% sw	50% sh
"bottom-right"	60% sw	50% sh	40% sw	50% sh
"left-half"	0	0	50% sw	sh
"right-half"	50% sw	0	50% sw	sh

Unknown slot-name strings raise a loud-error at panel.register (so typos surface immediately, not in the next frame's render). Custom functions that error at runtime fall back to "center" with an engine.print warning.

Bounds are re-resolved every render frame, so layout-slots react to screen-resizes automatically.

Multi-Active API

• panel.open(id) — opens; does NOT close other open panels. If already open, brings to front (re-focused).
• panel.close(id) — closes that specific id.
• panel.close() — bw-compat: closes the focused (last-opened) panel.
• panel.is_open(id) — id-specific.
• panel.is_open() — bw-compat: any panel open.
• panel.is_pausing() — true if ANY open panel has pause_on_open=true.

Hit-Test Order

Input events dispatch through panels in reverse open-order (last- opened first). A click that hits a panel's bounds is consumed by that panel and not propagated further. A click that misses all panels is dropped (v0.2.0 does not route to game; v0.3+ may add that).

Wheel events route to the focused (last-opened) panel only.

Bw-Compat Guarantee

All v0.1.1 callers (register(id, widget) without opts, open(id), close(), is_open()) keep their existing semantics. The one behavioral change: panel.open(A) followed by panel.open(B) now leaves BOTH open instead of replacing A.

If you relied on the v0.1.1 "open(B) closes A" behavior, call panel.close() before panel.open(B) to keep the single-active idiom.

Test backdoors (v0.2.0 additions)

• panel._test_reset_all() — clears widgets + windows + open_order + ctx_menu (theme + triggers preserved).
• panel._test_get_open_ids() — array of currently-open ids in open-order (last = focused).
• panel._test_get_focused_id() — last-opened id, or nil.
• panel._test_get_window_bounds(id) — resolved {x,y,w,h} for an open window, or nil if not open.
• panel._test_get_screen_size() — current screen size used by layouts.

Theme Schema

Key	Default	Description
bg_color	0x202020F0	Panel background (RGBA packed)
border_color	0x808080FF	Panel border
text_color	0xE0E0E0FF	Primary text
text_color_dim	0xA0A0A0FF	Dimmed / secondary text
selection_color	0x404080FF	Row / item selection highlight
context_menu_bg	0x303030F8	Context-menu background
context_menu_hover	0x404060FF	Context-menu row hover
font_size_title	18	Title bar font size (px)
font_size_body	14	Content font size (px)
padding	8	Inner padding (px)
row_height	24	Row height for lists / menus (px)
panel_width_frac	0.5	Panel width as fraction of screen
panel_height_frac	0.7	Panel height as fraction of screen

Widget-Lifecycle-Contract

Widget render(ctx) is called each render frame while the widget is open. Widget handle_input(ctx, event) is called for each dispatched input event.

Both receive a ctx table:

ctx = {
    bounds = {
        x = number,  -- content area top-left x
        y = number,  -- content area top-left y
        w = number,  -- content area width
        h = number,  -- content area height
    },
    theme      = table,   -- current merged theme (read-only by convention)
    is_focused = bool,    -- true when this widget is the focused one (last-opened)
}

The event table passed to handle_input:

-- Mouse click:
event = { kind = "click", x = number, y = number, button = "left"|"right" }

-- Mouse wheel:
event = { kind = "wheel", dy = number }  -- dy > 0 = scroll up, dy < 0 = scroll down

Context-menu intercepts clicks before they reach handle_input. The widget calls panel.show_context_menu(x, y, actions) from within handle_input when a right-click (or any application-specific trigger) warrants a menu.

Glue-Pattern

Minimal module setup (copy-paste-able):

local panel = require("lib-core.panel")

-- 1. Register your widget once (e.g. in module init or M.load)
panel.register("inventory", {
    title         = "Inventory",
    pause_on_open = true,
    render        = function(ctx) inventory_ui.draw(ctx) end,
    handle_input  = function(ctx, event) inventory_ui.on_input(ctx, event) end,
})

-- 2. Bind a toggle key (optional; defaults to Tab)
panel.bind_default_trigger("i", "inventory")

-- 3. Wire into your module's update + render
function M.update(dt)
    panel.update(dt)
    if not panel.is_pausing() then
        -- normal game logic here
    end
end

function M.render()
    -- ... draw world ...
    panel.render()  -- draws panel overlay on top
end