Interactive Modelling and Rendering of Clouds Jesper Mosegaard , PhD - PowerPoint PPT Presentation

Click to edit Master title style Interactive Modelling and Rendering of Clouds Jesper Mosegaard , PhD Head of Computer Graphics Lab Alexandra Institute Denmark

Click to edit Master title style 19/03/15 Page 2

The Alexandra Institute Click to edit Master title style • Private not-for-profit company within IT – Technology transfer from University research through GTS institutes (Danish model) • Application oriented research • Consultancy for companies

Interdisciplinary collaboration Click to edit Master title style

Problem statement Click to edit Master title style 19/03/15 Page 5

… even more difficult Click to edit Master title style

Traditional workflow Click to edit Master title style • Simulating fluid dynamics is slow • Shaping through parameters is in-direct • Viewport does not represent final quality 19/03/15 Page 7 From https://vimeo.com/30189748

External video Click to edit Master title style

Taming the Elements Click to edit Master title style • User-guided procedural content generation with instant feedback to make even the most advanced setups possible. • High-quality real-time rendering which allows for continuous visual quality tweaking. • Less time spent waiting. – More time for what really matters – being creative.

This month tutorials featured in Click to edit Master title style Elementacular.com 19/03/15 10

Overview Click to edit Master title style Mesh Voxelization Floodfilling User- controlled Dilation & fractal distance evaluation approximation Distance Field Noise Field Image Whispy Field Raymarch Raymarch Light Fields

Data Representation Click to edit Master title style Antoine Bouthors et. al.: ”Interactive multiple anisotropic scattering in clouds”

Rasterization-based voxelization Click to edit Master title style "Octree-Based Sparse Voxelization Using The GPU Hardware Rasterizer" Cyril Crassin (NVIDIA), Simon Green (NVIDIA), in OpenGL Insights , July 2012

Voxelization Results Click to edit Master title style

Voxelization Results Click to edit Master title style

Overview Click to edit Master title style Mesh ✔ Voxelization Floodfilling User- controlled Dilation & fractal distance evaluation approximation Distance Field Noise Field Image Whispy Field Raymarch Raymarch Light Fields

Why do we need to floodfill? Click to edit Master title style • Voxelization produces voxels for each triangle fragment. – In practice a lot of geometry is self-intersecting. – We need the outer voxels for distance field calculation

Compute Shaders Click to edit Master title style • Easy-to-use general-purpose compute. • OpenGL 4.3 feature. • Very powerful coupled with Image load/store. – Read/write to 3D texture at arbitrary positions. – Perform atomic operations on storage.

Floodfilling on the GPU Click to edit Master title style • Two Compute Shaders – tag initial outside voxels (if visible from all three axes) – Iteratively grow voxels outside. Input mesh Thin voxelization Initial tagging Iterative growth

My ¡Cloud ¡

Thin ¡shell ¡voxeliza3on ¡

Seed ¡floodfill ¡

Itera3ve ¡floodfill ¡

Itera3ve ¡floodfill ¡

Itera3ve ¡floodfill ¡

Itera3ve ¡floodfill ¡

Itera3ve ¡floodfill ¡

Removing ¡internal ¡voxels ¡

Overview Click to edit Master title style Mesh ✔ Voxelization ✔ Floodfilling User- controlled Dilation & fractal distance evaluation approximation Distance Field Noise Field Image Whispy Field Raymarch Raymarch Light Fields

Dilation and Distance Estimation Click to edit Master title style • Single compute shader. • Propagate distance information from initial surface voxels: – If voxel is tagged as outside and not part of the initial surface, pull minimum distance. – Combine using imageAtomicMin. – Complicated by the fact that atomic operations only work on 32bit integers.

Ini3al ¡distances ¡to ¡triangles ¡

Distance ¡itera3on ¡1 ¡

Distance ¡itera3on ¡2 ¡

Map ¡to ¡densi3es ¡

Overview Click to edit Master title style Mesh ✔ Voxelization ✔ Floodfilling User- ✔ controlled Dilation & fractal distance evaluation approximation Distance Field Noise Field Image Whispy Field Raymarch Raymarch Light Fields

Making Some Noise Click to edit Master title style • Specialized compute shaders. • A major part of getting the look right. • Fractals based on GPU generated Simplex and Worley noise • Wispys based on gridless advection Based on Siggraph 2011 Course “Production Volume Rendering Systems”.

Making Some Noise Click to edit Master title style

Simplex ¡roughness ¡ Wispy ¡roughness ¡ 19/03/15 ¡ Page ¡38 ¡

Overview Click to edit Master title style Mesh ✔ Voxelization ✔ Floodfilling ✔ User- ✔ controlled Dilation & fractal distance evaluation approximation Distance Field Noise Field Image Whispy Field Raymarch Raymarch Light Fields

Real-time single scattering Click to edit Master title style

Lighting the Volumes Click to edit Master title style • Single- vs. multi-scatter of light in volumes Multi-scatter (FLD) Combination Single-scatter

Multi-scatter Click to edit Master title style D. Koerner, J. Portsmouth, F. Sadlo, T. Ertl, B. Eberhardt: Flux-Limited Diffusion for Multiple Scattering in Participating Media Computer Graphics Forum, vol. 33, no. 6, pp. 178-189, 2014. 19/03/15 Page 42

Overview Click to edit Master title style Mesh ✔ Voxelization ✔ Floodfilling User- ✔ ✔ controlled Dilation & distance fractal approximation evaluation Distance Field Noise Field Image Whispy Field ✔ Raymarch Raymarch Light Fields

Real-time single scattering Click to edit Master title style • Naïve approach: • Prohibitively slow for real-time.

Real-time single scattering Click to edit Master title style • Exploit the fact that in-scattered irradiance can be separated from primary ray absorption. • Update only when lights are dirtied. • March towards each light accumulating the irradiance into a separate light buffer using compute shader. • When raymarching – Use light buffer instead of marching to light.

Overview Click to edit Master title style Mesh ✔ Voxelization ✔ Floodfilling ✔ User- ✔ controlled Dilation & fractal distance evaluation approximation Distance Field Noise Field Image Whispy Field ✔ Raymarch ✔ Raymarch Light Fields

Future work Click to edit Master title style • Animation • Other plugins for real-time editing of natural effects • Integrate into later stages of the production pipeline

Users are what makes this interesting Click to edit Master title style

Click to edit Master title style Thank you for your attention Mail: jesper.mosegaard@alexandra.dk Twitter: @mosegaard LinkedIn: linkedin.com/in/mosegaard Please complete the Presenter Evaluation sent to you by email or through the GTC Mobile App. Your feedback is important!