A year of sunlight over a real hillside, computed in your tab

Annual sun hours for every one of 455k terrain cells at 63.44° N. One WGSL pass marches 32 azimuths per cell to build a horizon map — the terrain's own skyline, packed to a byte per direction — and a second pass sums the daylight that clears it, for ~1 300 sun positions across the year. After that, shadowing is a lookup, not a ray: the sun sweeping the slope below runs the same horizon test per vertex at 60 fps. The result is read back once and 48 cells are recomputed in TypeScript from the same sun geometry; the CPU-check row is that comparison, printed live. Click any slope to read that cell's own skyline out of the map — the whole horizon in every direction, with no search radius and no ray cast, because the answer was already computed. The query time printed under the plot is measured, not quoted.