Everything in the chapter, at once

A volumetric cloud, marched in real time

A bounding slab, a density field, transmittance accumulating by Beer–Lambert, in‑scattering weighted by a phase function, a second march toward the sun for shadowing, and early‑ray termination to pay for it all. Every term has its own slider — including the ones that break it. Drag to look around, then put the sun behind the cloud and raise g.

The render —

Drag to look around

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The medium what the cloud is

Coverage 0.46

Density σ_t 3.10

Phase g 0.45

Sun elevation 26°

Sun azimuth 68°

The march what it costs

View steps 48

Light steps 5

Stop when T < 0.020

Jitter the samples Wind

Samples per pixel, worst case—

Rays this frame—

Density evaluations per frame—

Frame rate

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Render resolution

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Cost of one light step

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Sun is

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Look at the third line of the cost panel. The nested light march is what makes volumetric rendering expensive: every one of the view samples spawns another handful of density evaluations, so the total is steps × (1 + lightSteps) per pixel and the light march is usually the larger half of it. Pull light steps down to 1 and the frame rate jumps while the cloud goes flat and loses its interior shadowing — that trade is the single biggest lever in any real cloud renderer, and it is why they cache the lighting into a low‑resolution volume, or reuse last frame's answer, rather than paying for it honestly at every sample. Then set view steps to 12 with jitter off and watch the banding from two demos ago reappear here, in a real image.