[mjohnson7cd]

Summary

Fixes storytold/artcraft#2081 - Rendering stops at frame 970/1570, PC lags until app closed on high-end system (i7-12700KF, RTX 3090, 32GB RAM).

Problem

GPU readback staging buffers accumulated unbounded when layer bounds changed every frame (animated scale, blur radius, growing shapes). Each 1080p RGBA f32 buffer ≈ 33 MB in system RAM. At 970 frames × 33 MB ≈ 32 GB, the system exhausted available memory.

The buffers are kept for reuse (up to 2 per size), but there was no limit on total memory across all sizes.

Solution

Capped GPU readback staging buffers to 256 MB total. When adding a new buffer would exceed the cap, drop buffers of other sizes while keeping the current size for reuse. Renders with consistent frame sizes still benefit from buffer reuse.

Implementation

Changed: crates/gpu/src/context.rs, crates/gpu/tests.rs (+34/-1)

• Added 256 MB budget for readback staging buffers
• Eviction policy: drop other sizes when budget exceeded, keep current size
• New test: readback_staging_stays_bounded_across_sizes

Test Results

Without fix: Test reads 120 different sizes (~480 MB), holds 620 MB, takes 28.5s (Apple M4/Metal)
With fix: Same test passes in 0.54s, stays within 256 MB budget

✓ cargo fmt
✓ cargo clippy --workspace --all-targets -- -D warnings
✓ cargo test -p effectcraft-gpu (204 tests passed)

Notes

• Verified on Metal backend; not tested on Windows/DX12/Vulkan with RTX 3090
• Would benefit from reporter's project file to confirm exact reproduction
• Small rebase conflict possible with open PRs GPU: resident effect stacks, in-frame texture reuse, upload-cache budget, stable footprint keys (#687) #688, Cache/GPU: adjustment footprint ignores the effect stack; upload starvation is reported (#687) #701 (also touch GPU cache code)

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— sent on behalf of @mjohnson7cd by Claude Code

[mjohnson7cd]

Hi @echelon! 👋

This PR has been ready for review for a while and addresses issue storytold/artcraft#2081 (rendering stops at 970/1570 fps, system exhaustion).

The fix caps GPU readback staging buffers to 256 MB to prevent unbounded memory growth when layer bounds change every frame. All tests pass (204 tests in effectcraft-gpu).

Is there anything blocking this from being merged, or any changes you'd like to see?

Thanks for your time reviewing! 🙏

— sent on behalf of @mjohnson7cd by Claude Code

[echelon]

Merged. Thank you for the contribution, @mjohnson7cd!

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