Module pass_timing 

Per-pass GPU timing on D3D12 via TIMESTAMP queries. The whole-frame timer lives in slots [0, 1] of each frame’s block; one pair per PassId follows (start at slot 2 + 2i, end at slot 3 + 2i). The shared query heap is sized for FRAMES such blocks; execute_graph issues an EndQuery before and after each pass’s encode_*, and the resolve at the end of the command list copies the whole block into the persistently-mapped readback buffer. The CPU reads the previous frame’s block at the top of draw_frame (after the matching fence wait gates the GPU writes) and publishes the per-pass microseconds into RenderStats.pass_times_us.

Layout reasoning. Keeping the whole-frame pair at the front of each block preserves the legacy gpu_frame_us indexing: the existing readback reads the first u64 pair of the frame’s block, exactly as before; only the per-frame stride changes. SsaoPrepass / SsaoKernel / ParticlesSim are bundled inside their parent encoders (see graph_exec.rs) so the sub-pass slots stay zero; the FogFroxel / Upscale / Transparent / Raymarch arms are no-ops on DirectX so their slots also stay zero. The shared StatHud.passes_text helper picks the top six non-zero entries by descending microseconds, so zero slots are naturally filtered out of the on-screen chip.

This is GPU-free slot-index arithmetic (no D3D12 types), so it lives in concinnity-render and its layout tests count toward coverage; the DirectX backend re-exports it under crate::directx::pass_timing.

Constants

FRAME_BLOCK_BYTES

Bytes consumed by one frame’s block in the readback buffer. Each slot is a u64 timestamp.

SLOTS_PER_FRAME

Per-frame block: [whole_frame_start, whole_frame_end, pass0_start, pass0_end, …, pass(PASS_COUNT-1)_start, pass(PASS_COUNT-1)_end]. 2 * (PASS_COUNT + 1) u64 slots.

Functions

frame_readback_byte_offset

Byte offset into the readback buffer where this frame’s block begins.

frame_resolve_start

First heap slot the per-frame ResolveQueryData should walk. Pair this with SLOTS_PER_FRAME as the count.

pass_pair

Slot indices for pass’s start + end timestamps within the heap.

whole_frame_pair

Slot indices for the whole-frame timestamp pair within the heap. Matches the legacy layout (whole-frame still at the first pair of each frame’s block) so the existing gpu_frame_us readback only needs a stride adjustment.