Data containing spherical harmonics coefficients that describe the light’s intensity in all directions.
- iOS 9.0+
- macOS 10.11+
- tvOS 9.0+
- Model I/O
Spherical harmonic coefficients describe the distribution of light around a light source with less high-frequency detail than a cube map texture, but they can be used more efficiently in real-time rendering. Use the
generate method to create spherical harmonics data based on the light’s photometry data.
The data is an array of 32-bit floating-point values, containing three noninterleaved data sets corresponding to the red, green, and blue sets of coefficients. The array’s length is determined by the
At level 0, the array has 1 coefficient (3 values).
At level 1, the array has 4 coefficients (3 sets of 4 values, 12 values total).
At level 2, the array has 9 coefficients (3 sets of 9 values, 27 values total).
At level 3, the array has 16 coefficients (3 sets of 16 values, 48 values total).
Spherical harmonics levels beyond 3 are not supported.
For example, the code below shows how to access the second coefficient at level 2. (Note, however, that typically a renderer passes the entire data buffer to a GPU-based shader and uses equivalent shader code to extract individual coefficients.)