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Worldlight

Soft shadows retain their detail in small features thanks to the multiresolution maps

One of our more recent research projects is a highly realistic lighting and shadowing solution for complex outdoor environments.

Worldlight uses a diffuse PRT solution to provide soft light and shadows resulting from direct and indirect illumination by an HDR skydome. On top of this, it adds a soft directional sunlight term which is correctly shadowed by the world geometry.

Gallery

Tone-mapped with black and white print film

Skull lit with local lighting computed from the environment

Shadow-mapped sunlight with PRT global illumination

About Worldlight

Objects in the world are lit using similar techniques, with their diffuse and specular lighting environments being created on the fly from their surroundings. This anchors the objects in the world and ensures that their lighting is always an accurate match for the local environment.

The resulting HDR image is then tone-mapped for display using one of several tone-mapping algorithms in real-time.

Second Intention developed Worldlight to investigate the state of the art in realtime rendering and bring together several techniques which have been presented to the real-time community over the last year but not thoroughly explored or integrated. If you are interested in Worldlight, how it works, and where it could go next, please contact us for more information.

More information

Paul Debevec’s research site – source of the skydome maps
Jonathon Blow’s HappyCake, which uses a similar shadowing technique
D3DX PRT documentation – a good starting point

Key features

Efficient PRT mesh format using 12 bytes per vertex – only as much data as a floating-point normal!
CPCA compression allowing arbitrary order of PRT simulation with the same per-vertex size and runtime cost. Higher orders cost more CPU time and CPCA basis table storage, but the GPU cost remains constant.
Multiresolution shadow maps giving crisp shadows both close-up on small details and in the distance on large buildings. Shadow map selection avoids use of the stencil buffer completely
Depth guided screen-space shadow filtering for soft shadows without depth artifacts
Local cubemaps for both specular lighting and PRT Spherical Harmonic diffuse lightsource generation
Real-time implementation of Geigel and Musgrave tonemapping. This simulates the nonlinear behaviour of different negative and print film emulsions allowing the user to input film characteristic curve data and see the real-time world rendered as though photographed with the film they have selected.