QuaternionEngine/docs/FrameResources.md

Frame Resources: Per-Frame Command, Sync, and Transient Descriptors

Per-frame struct that owns the command buffer, semaphores/fence, a transient descriptor allocator, and a small deletion queue. Frames are indexed by FRAME_OVERLAP (currently 2) and rotated by _frameNumber in VulkanEngine.

• File: src/core/frame_resources.h/.cpp

Responsibilities

• Command recording: _mainCommandBuffer allocated from a per-frame _commandPool with RESET flag.
• Synchronization: _swapchainSemaphore (image acquired), _renderSemaphore (render finished), _renderFence (CPU wait per frame).
• Transient descriptors: _frameDescriptors is a DescriptorAllocatorGrowable cleared every frame via clear_pools().
• Lifetime: _deletionQueue holds lambdas for transient GPU objects created during the frame (buffers/images) and is flushed at the start of the next frame.

Frame Flow (engine side)

• Start of frame:
  • Wait on _renderFence (previous GPU work for this frame index), flush _deletionQueue, and clear _frameDescriptors pools.
  • Acquire swapchain image signaling _swapchainSemaphore.
  • Reset _renderFence and _mainCommandBuffer; begin recording.
  • Publish currentFrame pointer and drawExtent on EngineContext.
• Graph build and execute:
  • Render Graph is cleared and rebuilt; ResourceManager::register_upload_pass(...) is added first if there are pending uploads.
  • Passes record using the published currentFrame to allocate transient descriptor sets and to enqueue per-frame cleanups.
• Submit and present:
  • Submit cmd with wait on _swapchainSemaphore and signal _renderSemaphore, fence _renderFence.
  • Present waits on _renderSemaphore.

Do/Don’t

• Do use currentFrame->_frameDescriptors for descriptor sets that live only for this frame.
• Do push transient resource destruction into currentFrame->_deletionQueue.
• Don’t stash per-frame descriptor sets across frames — they are reset on clear_pools().

Extending

• If a pass needs additional short-lived command buffers, allocate them from _commandPool and reset per frame.
• If you add frames-in-flight, update FRAME_OVERLAP and verify fences/semaphores and swapchain image acquisition logic.