H3Error H3_EXPORT()

in h3_localij.c [677:727]

• 35 lines of code
• 7 McCabe index (conditional complexity)

H3Error H3_EXPORT(gridPathCells)(H3Index start, H3Index end, H3Index *out) {
    int64_t distance;
    H3Error distanceError = H3_EXPORT(gridDistance)(start, end, &distance);
    // Early exit if we can't calculate the line
    if (distanceError) {
        return distanceError;
    }

    // Get IJK coords for the start and end. We've already confirmed
    // that these can be calculated with the distance check above.
    CoordIJK startIjk = {0};
    CoordIJK endIjk = {0};

    // Convert H3 addresses to IJK coords
    H3Error startError = cellToLocalIjk(start, start, &startIjk);
    if (NEVER(startError)) {
        // Unreachable because this was called as part of gridDistance
        return startError;
    }
    H3Error endError = cellToLocalIjk(start, end, &endIjk);
    if (NEVER(endError)) {
        // Unreachable because this was called as part of gridDistance
        return endError;
    }

    // Convert IJK to cube coordinates suitable for linear interpolation
    ijkToCube(&startIjk);
    ijkToCube(&endIjk);

    double invDistance = distance ? 1.0 / (double)distance : 0;
    double iStep = (double)(endIjk.i - startIjk.i) * invDistance;
    double jStep = (double)(endIjk.j - startIjk.j) * invDistance;
    double kStep = (double)(endIjk.k - startIjk.k) * invDistance;

    CoordIJK currentIjk = {startIjk.i, startIjk.j, startIjk.k};
    for (int64_t n = 0; n <= distance; n++) {
        cubeRound((double)startIjk.i + iStep * n,
                  (double)startIjk.j + jStep * n,
                  (double)startIjk.k + kStep * n, &currentIjk);
        // Convert cube -> ijk -> h3 index
        cubeToIjk(&currentIjk);
        H3Error currentError = localIjkToCell(start, &currentIjk, &out[n]);
        if (currentError) {
            // The cells between `start` and `end` may fall in pentagon
            // distortion.
            return currentError;
        }
    }

    return E_SUCCESS;
}