From be2270b1e0b99a72ad38f0ac96e6d35dc50eb326 Mon Sep 17 00:00:00 2001
From: John McCardle <john@ffwf.net>
Date: Tue, 16 Dec 2025 21:25:50 +0000
Subject: [PATCH] Add Grid System

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+# Grid System
+
+The Grid System is McRogueFace's core spatial container for roguelike game maps. It provides tilemap rendering, entity management, FOV (field of view), and pathfinding integration with libtcod.
+
+## Quick Reference
+
+**Related Issues:**
+- [#113](../issues/113) - Batch Operations for Grid (Open - Tier 1)
+- [#124](../issues/124) - Grid Point Animation (Open - Tier 1)
+- [#150](../issues/150) - User-driven Layer Rendering (Closed - Implemented)
+- [#148](../issues/148) - Dirty Flag RenderTexture Caching (Closed - Implemented)
+- [#147](../issues/147) - Dynamic Layer System (Closed - Implemented)
+- [#123](../issues/123) - Chunk-based Grid Rendering (Closed - Implemented)
+
+**Key Files:**
+- `src/UIGrid.h` / `src/UIGrid.cpp` - Main grid implementation
+- `src/GridLayers.h` / `src/GridLayers.cpp` - ColorLayer and TileLayer
+- `src/UIGridPoint.h` - Individual grid cell (walkability, transparency)
+- `src/UIGridPointState.h` - Per-entity perspective/knowledge
+- `src/UIEntity.h` / `src/UIEntity.cpp` - Entity system (lives on grid)
+
+**API Reference:**
+- See [mcrfpy.Grid](../docs/api_reference_dynamic.html#Grid) in generated API docs
+- See [mcrfpy.Entity](../docs/api_reference_dynamic.html#Entity) in generated API docs
+
+## Architecture Overview
+
+### Three-Layer Design
+
+The Grid System uses a three-layer architecture for sophisticated roguelike features:
+
+1. **Visual Layer** (Rendering Layers)
+   - What's displayed: tile sprites, colors, overlays
+   - Implemented via `ColorLayer` and `TileLayer` objects
+   - Multiple layers per grid with z_index ordering
+   - Files: `src/GridLayers.h`, `src/GridLayers.cpp`
+
+2. **World State Layer** (`TCODMap`)
+   - Physical properties: walkable, transparent, cost
+   - Used for pathfinding and FOV calculations
+   - Integration: libtcod via `src/UIGrid.cpp`
+
+3. **Perspective Layer** (`UIGridPointState`)
+   - Per-entity knowledge: what each entity has seen/explored
+   - Enables fog of war, asymmetric information
+   - File: `src/UIGridPointState.h`
+   - **Note:** Python access currently limited - see Known Issues
+
+This architecture follows proven patterns from Caves of Qud, Cogmind, and DCSS.
+
+### Dynamic Layer System
+
+Grids support multiple rendering layers that can be added/removed at runtime:
+
+| Layer Type | Purpose | Methods |
+|------------|---------|---------|
+| `ColorLayer` | Solid colors per cell (fog, highlights) | `set(x, y, color)`, `at(x, y)`, `fill(color)` |
+| `TileLayer` | Texture sprites per cell (terrain, items) | `set(x, y, sprite_index)`, `at(x, y)`, `fill(index)` |
+
+**z_index semantics:**
+- Negative z_index: Renders **below** entities
+- Zero or positive z_index: Renders **above** entities
+- Lower z_index renders first (behind higher z_index)
+
+```python
+# Create grid with no default layers
+grid = mcrfpy.Grid(grid_size=(50, 50), pos=(100, 100), size=(400, 400), layers={})
+
+# Add layers explicitly
+background = grid.add_layer("color", z_index=-2)    # Furthest back
+tiles = grid.add_layer("tile", z_index=-1)          # Above background, below entities
+fog_overlay = grid.add_layer("color", z_index=1)    # Above entities (fog of war)
+
+# Access existing layers
+for layer in grid.layers:
+    print(f"{type(layer).__name__} at z={layer.z_index}")
+
+# Remove a layer
+grid.remove_layer(fog_overlay)
+```
+
+### Grid → Entity Relationship
+
+**Entity Lifecycle:**
+- Entities live on exactly 0 or 1 grids
+- `grid.entities.append(entity)` sets `entity.grid = grid`
+- `grid.entities.remove(entity)` sets `entity.grid = None`
+- Entity removal handled automatically on grid destruction
+
+**Spatial Queries:**
+- Currently: Linear iteration through entity list
+- Planned: SpatialHash for O(1) lookups (see [#115](../issues/115))
+
+## Sub-Pages
+
+- [[Grid-Rendering-Pipeline]] - How grid renders each frame (chunks, dirty flags, caching)
+- [[Grid-TCOD-Integration]] - FOV, pathfinding, walkability
+- [[Grid-Entity-Lifecycle]] - Entity creation, movement, removal
+
+## Common Tasks
+
+### Creating a Grid
+
+```python
+import mcrfpy
+
+# Create grid with default tile layer
+grid = mcrfpy.Grid(
+    grid_size=(50, 50),      # 50x50 cells
+    pos=(100, 100),          # Screen position
+    size=(400, 400),         # Viewport size in pixels
+    texture=my_texture       # Texture for default TileLayer
+)
+
+# Or create with specific layer configuration
+grid = mcrfpy.Grid(
+    grid_size=(50, 50),
+    pos=(100, 100),
+    size=(400, 400),
+    layers={"terrain": "tile", "highlights": "color"}
+)
+
+# Or start empty and add layers manually
+grid = mcrfpy.Grid(grid_size=(50, 50), pos=(100, 100), size=(400, 400), layers={})
+terrain = grid.add_layer("tile", z_index=-1, texture=my_texture)
+
+# Add to scene
+mcrfpy.sceneUI("game").append(grid)
+```
+
+### Setting Tile Properties
+
+```python
+# Access layers for visual properties
+tile_layer = grid.layers[0]  # First layer (usually tiles)
+tile_layer.set(x, y, 42)     # Set sprite index at cell
+
+color_layer = grid.add_layer("color", z_index=-2)
+color_layer.set(x, y, mcrfpy.Color(64, 64, 128))  # Blue tint
+
+# Access grid point for world properties
+point = grid.at(x, y)
+point.walkable = True      # Can entities walk here?
+point.transparent = True   # Can see through for FOV?
+```
+
+### FOV and Pathfinding
+
+```python
+# Compute field of view from position
+grid.compute_fov(entity.grid_x, entity.grid_y, radius=10)
+
+# Check if cell is visible
+if grid.is_in_fov(target_x, target_y):
+    print("Target is visible!")
+
+# A* pathfinding
+path = grid.find_path(start_x, start_y, end_x, end_y)
+
+# Dijkstra maps for AI
+grid.compute_dijkstra([(goal_x, goal_y)])
+distance = grid.get_dijkstra_distance(entity.grid_x, entity.grid_y)
+path_to_goal = grid.get_dijkstra_path(entity.grid_x, entity.grid_y)
+```
+
+### Mouse Events
+
+Grids support mouse interaction at both the grid level and cell level:
+
+```python
+# Grid-level events (screen coordinates)
+def on_grid_click(x, y, button):
+    print(f"Grid clicked at pixel ({x}, {y}), button {button}")
+
+grid.on_click = on_grid_click
+grid.on_enter = lambda: print("Mouse entered grid")
+grid.on_exit = lambda: print("Mouse left grid")
+grid.on_move = lambda x, y: print(f"Mouse at ({x}, {y})")
+
+# Cell-level events (grid coordinates)
+def on_cell_click(grid_x, grid_y):
+    print(f"Cell ({grid_x}, {grid_y}) clicked!")
+    point = grid.at(grid_x, grid_y)
+    # Do something with the cell...
+
+grid.on_cell_click = on_cell_click
+grid.on_cell_enter = lambda x, y: print(f"Entered cell ({x}, {y})")
+grid.on_cell_exit = lambda x, y: print(f"Left cell ({x}, {y})")
+
+# Query currently hovered cell
+if grid.hovered_cell:
+    hx, hy = grid.hovered_cell
+    print(f"Hovering over ({hx}, {hy})")
+```
+
+### Camera Control
+
+```python
+# Center viewport on a position (pixel coordinates within grid space)
+grid.center = (player.grid_x * 16 + 8, player.grid_y * 16 + 8)
+
+# Or set components individually
+grid.center_x = player.grid_x * 16 + 8
+grid.center_y = player.grid_y * 16 + 8
+
+# Zoom (1.0 = normal, 2.0 = 2x zoom in, 0.5 = zoom out)
+grid.zoom = 1.5
+```
+
+## Performance Characteristics
+
+**Implemented Optimizations:**
+- **Chunk-based rendering** ([#123](../issues/123)): Large grids divided into chunks, only visible chunks rendered
+- **Dirty flag system** ([#148](../issues/148)): Layers track changes, skip redraw when unchanged
+- **RenderTexture caching**: Each chunk cached to texture, reused until dirty
+- **Viewport culling**: Only cells within viewport are processed
+
+**Current Performance:**
+- Grids of 1000x1000+ cells render efficiently
+- Static scenes near-zero CPU (cached textures reused)
+- Entity rendering: O(visible entities)
+
+**Profiling:** Use the F3 overlay or `mcrfpy.setTimer()` with `mcrfpy.getMetrics()` to measure grid performance. See [[Performance-and-Profiling]].
+
+## Known Issues & Limitations
+
+**Current Limitations:**
+- **FOV Python access limited:** `compute_fov()` works but fog-of-war overlay must be managed manually via color layers. Per-entity perspective (`UIGridPointState`) not yet exposed to Python. See [#113 discussion](../issues/113).
+- No tile-level animation yet (planned: [#124](../issues/124))
+- Entity spatial queries are O(n) (planned: SpatialHash [#115](../issues/115))
+
+**Workarounds:**
+- For fog of war: Use a `ColorLayer` with positive z_index, update cell colors based on `is_in_fov()` results
+- For entity queries: Use list comprehension filtering on `grid.entities`
+
+## Related Systems
+
+- [[UI-Component-Hierarchy]] - Grid inherits from UIDrawable
+- [[Animation-System]] - Grid properties are animatable (pos, zoom, center, etc.)
+- [[Performance-and-Profiling]] - Grid rendering instrumented with metrics
+- [[Entity-Management]] - Entities live within Grid containers
+
+---
+
+*Last updated: 2025-11-29*
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