Phase 1: RHI Interface Segregation Cleanup

[MichaelFisher1997]

Phase 1: RHI Interface Segregation Cleanup

Goal

Finish the RHI interface split by removing deprecated methods from IRenderContext and routing consumers through focused interfaces.

Why this matters

src/engine/graphics/rhi.zig still exposes a broad IRenderContext with methods that already belong to smaller interfaces. That weakens ISP and keeps the rest of the codebase coupled to legacy convenience methods.

Parallel Tasks

Issue 1.1: Remove computeSSAO from IRenderContext

• Type: refactor / solid
• Scope: src/engine/graphics/rhi.zig
• Problem: computeSSAO is duplicated on IRenderContext even though ISSAOContext already exists.
• Work:
  • Remove computeSSAO from IRenderContext.VTable
  • Remove the IRenderContext.computeSSAO() forwarding method
  • Update any direct callers to use rhi.ssao() or rhi.ssao().compute(...)
• Acceptance criteria:
  • IRenderContext no longer exposes SSAO-specific behavior
  • Build passes
  • No remaining call sites depend on the removed method
• Parallel-safe: yes, if no one else is editing the same call sites

Issue 1.2: Remove drawDebugShadowMap from IRenderContext

• Type: refactor / solid
• Scope: src/engine/graphics/rhi.zig
• Problem: debug overlay behavior is still embedded in the general render context.
• Work:
  • Remove drawDebugShadowMap from IRenderContext.VTable
  • Remove the IRenderContext.drawDebugShadowMap() forwarding method
  • Ensure the debug overlay path uses IDebugOverlayContext
• Acceptance criteria:
  • Debug shadow rendering is accessed through the dedicated interface only
  • Build passes
• Parallel-safe: yes

Issue 1.3: Route SSAO calls through ISSAOContext in the render graph

• Type: refactor / solid
• Scope: src/engine/graphics/render_graph.zig, call sites that build SceneContext
• Problem: the render graph already receives ISSAOContext, but the codebase still needs a clean, explicit dependency path.
• Work:
  • Audit SceneContext construction and ensure SSAO work always uses ssao_ctx
  • Remove any remaining render-context-based SSAO assumptions
  • Update comments/docs to reflect the focused interface
• Acceptance criteria:
  • Render graph code only references ISSAOContext for SSAO work
  • No lingering comments or docs describe SSAO as a render-context concern
• Parallel-safe: yes

Dependencies

• None required before Phase 1

Verification

• nix develop --command zig build test
• nix develop --command zig build

[github-actions]

This is a valid refactoring issue (Feature Request / Refactor) with well-defined scope.

Analysis

Issue 1.1 & 1.2 (remove computeSSAO and drawDebugShadowMap from IRenderContext):

• Both methods are present in IRenderContext.VTable at rhi.zig:687-689 with existing TODO markers (Refactor: Relocate computeSSAO to SSAOSystem #225, Refactor: Relocate drawDebugShadowMap to Debug Overlay System #226)
• RenderContext has forwarding methods at lines 281-286
• The Vulkan backend wires these at rhi_vulkan.zig:943-944
• No external call sites found - these methods are only called internally within the RHI implementation
• The underlying implementations (computeSSAO at rhi_vulkan.zig:837, drawDebugShadowMap at rhi_vulkan.zig:849) are correctly shared with ISSAOContext.VTable and IDebugOverlayContext.VTable respectively

Issue 1.3 (route SSAO through ISSAOContext):

• Already implemented in render_graph.zig:285: ctx.ssao_ctx.compute(proj, inv_proj);
• SceneContext at line 60 correctly exposes ssao_ctx: ISSAOContext

Risks

• None significant. The methods being removed are already duplicated in dedicated interfaces (ISSAOContext, IDebugOverlayContext), and no external callers depend on them.
• The implementation functions themselves (computeSSAO, drawDebugShadowMap in rhi_vulkan.zig) must be retained as they service the dedicated interface vtables.

Recommendation

The issue accurately describes the work. All three sub-tasks are parallel-safe and low-risk. The acceptance criteria are achievable.

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