Realistic and Fast Cloud Rendering

Niniane Wang
Microsoft Research

This paper appears in issue Volume 9, Number 3.
Purchase this issue from the akpeters.com web site.

Abstract

Clouds are an important aspect of rendering outdoor scenes. This paper describes a cloud system that extends texture splatting on particles to model a dozen cloud types (e.g., stratus, cumulus congestus, cumulonimbus), an improvement over earlier systems that modeled only one type of cumulus. We also achieve fast real-time rendering, even for scenes of dense overcast coverage, which was a limitation for previous systems.

We present a new shading model that uses artist-driven controls rather than a programmatic approach to approximate lighting. This is suitable when fine-grained control over the look-and-feel is necessary, and artistic resources are available. We also introduce a way to simulate cloud formation and dissipation using texture splatted particles.

Author Information

Niniane Wang, Microsoft Research, 340 Central Avenue, Mountain View, CA 94043 niniane@gmail.com

Video

[Title frame from video]

View or download a 5-minute narrated video (49M .mpg) illustrating and demonstrating the techniques of this paper.

Screenshots

The following are screenshots from Microsoft Flight Simulator: A Century of Flight, for which the techniques of this paper were developed. Click on a thumbnail to view the high-resolution image.

[A screenshot]
[A screenshot]
[A screenshot]
[A screenshot]

Figures

The following are all the figures from the paper. Click on a thumbnail to view the high-resolution image.

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Figure 1. Scene of realistic clouds at sunset.

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Figure 2. Frontal view of a single cloud with sprites outlined.

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Figure 3. Boxes in 3D Studio Max representing a square region of clouds.

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Figure 4. After running our script, the boxes from Figure 3 are filled in with textured sprites.

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Figure 5. Scene showing three of our ten cloud types: a lower layer of stratus, middle layer of cumulus congestus, and a high layer of altocumulus.

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Figure 6. Sheet of 16 cloud sprite textures.

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Figure 7. Cloud prior to dissipation.

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Figure 8. Cloud edges are fading out.

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Figure 9. Cloud is mostly faded out.

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Figure 10. Ambient shading through vertical color levels.

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Figure 11. Directional shading.

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Figure 12. Rendering clouds onto an impostor.

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Figure 13. Ring of impostors around the camera. Couds within the ring are rendered three-dimensionally.

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Figure 14. Thick overcast layer covering the sky.

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Figure 15. Chart comparing performance with and without impostors, on two systems with different CPU speeds.

BibTeX Entry

@article{Wang04,
  author = "Niniane Wang",
  title = "Realistic and Fast Cloud Rendering",
  journal = "journal of graphics tools",
  volume = "9",
  number = "3",
  pages = "21-40",
  year = "2004",
}