Adds a sub-grid system where grids larger than 64x64 cells are automatically
divided into 64x64 chunks, each with its own RenderTexture for incremental
rendering. This significantly improves performance for large grids by:
- Only re-rendering dirty chunks when cells are modified
- Caching rendered chunk textures between frames
- Viewport culling at the chunk level (skip invisible chunks entirely)
Implementation details:
- GridChunk class manages individual 64x64 cell regions with dirty tracking
- ChunkManager organizes chunks and routes cell access appropriately
- UIGrid::at() method transparently routes through chunks for large grids
- UIGrid::render() uses chunk-based blitting for large grids
- Compile-time CHUNK_SIZE (64) and CHUNK_THRESHOLD (64) constants
- Small grids (<= 64x64) continue to use flat storage (no regression)
Benchmark results show ~2x improvement in base layer render time for 100x100
grids (0.45ms -> 0.22ms) due to chunk caching.
Note: Dynamic layers (#147) still use full-grid textures; extending chunk
system to layers is tracked separately as #150.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
