Resolve Issue #19: Remaining Audit Fixes - #23

Summary

This PR addresses the unresolved items from Issue #19 that were noted as "NOT RESOLVED". It builds upon the critical fixes by adding performance optimizations, test infrastructure, and further architectural improvements.

Fixes #19.

Addressed Issues

1. Monolithic App Struct

• Status: RESOLVED.
• Action: Decomposed App struct by extracting subsystems:
  • WindowManager (SDL/Context)
  • RenderSystem (RHI/Resources)
  • MapController (Map interaction/rendering logic) - New in this PR
  • MenuContext (Menu UI logic)
    App is now a focused orchestrator (~480 lines vs original >1000).

2. Buffer Recreation on Mesh Update (P2)

• Status: RESOLVED.
• Action: Implemented buffer pooling in src/world/chunk_mesh.zig. ChunkMesh now tracks buffer capacity and reuses existing buffers if the new mesh fits, resizing only when necessary (using power-of-2 growth). This eliminates the costly destroy/create cycle on every update.

3. Host-Visible Memory (P2)

• Status: RESOLVED.
• Action: Implemented staging buffers in src/engine/graphics/rhi_vulkan.zig.
  • createBuffer now selects DEVICE_LOCAL memory for vertex and index buffers.
  • uploadBuffer uses a temporary staging buffer to transfer data to the GPU, ensuring optimal rendering performance.

4. No Testing Infrastructure

• Status: RESOLVED.
• Action: Added src/tests.zig with unit tests and configured a test step in build.zig. CI now runs these tests.

5. Inefficient Chunk Rendering

• Status: RESOLVED.
• Action: Replaced linear iteration of the chunk map with a spatial grid loop in World.render.
  • Iterates only coordinates within render_distance.
  • Collects visible chunks into visible_chunks list to optimize the double-pass (solid/fluid) rendering.
  • Drastically reduces CPU overhead for large worlds.

Verification

• zig build test passes.
• zig build run -- --backend vulkan runs successfully.