Buoyancy Performance & Optimization

The Buoyancy system in Planetary Oceans calculates wave displacement on the CPU to apply physics forces to floating objects.

Asynchronous Computation

CPU FFT calculations run on background worker threads using ISPC's (Intel SPMD Program Compiler) parallel task system. They do not block the game thread, so the performance cost shows up as increased overall CPU usage rather than frame time spikes. This means:

• Your game thread remains responsive even during FFT computation

However, if your CPU cores are already saturated, additional FFT work can still impact frame rate indirectly through resource contention.

This page covers performance considerations and the new per-cascade CPU compute controls that allow you to fine-tune buoyancy performance based on your specific needs.

Understanding FFT Cascades

Planetary Oceans uses 4 FFT cascades to represent different wave frequencies:

• Cascade 0: Shortest waves (ripples) — ~25m tile size by default

• Cascade 1: Medium-short waves — ~28m tile size

• Cascade 2: Medium-long waves — ~432m tile size

• Cascade 3: Longest waves (swell) — ~2000m tile size

All 4 cascades are combined to create the final ocean surface you see. The GPU always renders all cascades regardless of CPU settings.

Per-Cascade CPU Compute Toggle

Starting in version 2.1, you can independently enable or disable each cascade for CPU buoyancy calculations. This is found in the Buoyancy section of BP_PlanetaryOcean:

• Compute Cascade 0 on CPU (shortest waves)

• Compute Cascade 1 on CPU

• Compute Cascade 2 on CPU

• Compute Cascade 3 on CPU (longest waves / swell)

Default: All cascades enabled (preserves behavior from previous versions)

How It Works

When you disable a cascade:

• GPU rendering continues — the ocean surface visually displays all wave frequencies

• CPU buoyancy ignores that cascade — floating objects don't respond to those wave frequencies

• Performance improves — each disabled cascade reduces buoyancy computation cost

The visual ocean surface and physical buoyancy are intentionally decoupled. If you disable short-wave cascades (0 and 1), you'll still see small ripples on the water, but large ships won't react to them — which is physically correct, as large vessels don't respond noticeably to small ripples.

Performance Benchmarks

Performance was measured with a 256×256 FFT grid and AVX2 CPU (AMD Ryzen 9 5950X) on a typical scene:

Configuration	CPU Time	Speedup vs All
All 4 cascades (default)	8.0 ms	1.0×
Cascades 2 + 3 only	4.0 ms	2.0×
Cascade 3 only	2.0 ms	4.0×

The measured milliseconds represent worker thread time, not game thread stalls. On multi-core CPUs, this work happens in parallel with gameplay logic.

Each disabled cascade saves approximately 2.0 ms of CPU time per buoyancy update.

Recommended Configurations

Choose cascade settings based on which cascades make the most impact on the ocean shape (it depends on your per-cascade parameters) and based on the size of your floating objects:

Large Ships (>20 meters): Cascade 3 (or 2) only

Medium Boats (5-20 meters): Cascades 2 + 3 (or 1 + 2)

Small Boats and characters (<5 meters): Cascades 1 + 2 + 3 (or all 4)

Performance Debugging

To monitor buoyancy CPU cost in real-time, enable Show CPU FFT Performance in the Buoyancy section of the ocean actor:

✓ Show CPU FFT Performance

Buoyancy calculations run at the rate specified by Buoyancy Update Tick Rate (default: 0.15 seconds). If you need more responsive physics, reduce this value — but remember each update costs the full FFT calculation time.