Resumed to project. INIT

notes/05-ui_renderer.md

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+# UI Renderer
+
+## Current state
+
+No UI primitives exist. The framebuffer is currently filled by the game world only
+(`render_viewport` in `game.rs`: tile pass + entity sprite pass). `pixelhelper.rs` has
+low-level pixel/blit helpers but nothing higher-level.
+
+## Goal
+
+Draw common roguelike UI elements (panels, borders, HUD bars, etc.) procedurally into the
+`u8` framebuffer, composited on top of the game world.
+
+## Design notes
+
+The virtual resolution is 320×240, so UI layout should be designed in those pixel units.
+
+Likely primitives needed (built on top of `pixelhelper.rs`):
+
+- `fill_rect(frame, x, y, w, h, color)` — solid filled rectangle
+- `draw_rect(frame, x, y, w, h, color)` — 1-pixel border rectangle
+- `draw_border_box(frame, x, y, w, h, tileset)` — box drawn with corner/edge tiles from
+  a tileset (classic roguelike panel look)
+- `draw_hbar(frame, x, y, w, value, max, fg, bg)` — horizontal progress/HP bar
+
+Panels are typically fixed regions of the screen (e.g. a status bar at the bottom 40px,
+a message log on the right). Hard-coding these regions first is fine; extract to a layout
+system only if needed.
+
+The UI layer draws after the world layer so it always appears on top. Draw order within
+the UI should be back-to-front (backgrounds before text).
+
+## Open questions
+
+- Tileset-based borders vs. line-drawing: which look are we going for?
+- Does the message log need scrolling? Probably not at first.