Function generateRivers

src/OpenLoco/src/Map/MapGenerator/MapGenerator.cpp:72–145

    }

    static void generateRivers(const Scenario::Options& options, HeightMap& heightMap)
    {
        for (auto i = 0; i < options.numRiverbeds; i++)
        {
            auto& gs = getGameState();
            const auto riverEastWest = gs.rng.randBool();
            const auto riverWidth = gs.rng.randNext(options.minRiverWidth, options.maxRiverWidth);
            const auto riverbedHeight = std::max<uint8_t>(gs.seaLevel > 0 ? gs.seaLevel - 1 : 1, options.minLandHeight);

            // We'll be varying the bank width as we meander
            auto riverbankWidth = options.riverbankWidth;
            auto totalRiverWidth = riverWidth + 2 * riverbankWidth;
            auto easternBankOffset = riverWidth + riverbankWidth;

            // Pivot: generate a random X position
            auto xStartPos = getGameState().rng.randNext(0.15 * heightMap.width, 0.85 * heightMap.width);
            for (auto yPos = 0; yPos < heightMap.height; yPos++)
            {
                for (auto xOffset = 0; xOffset < totalRiverWidth; xOffset++)
                {
                    auto pos = TilePos2(xStartPos + xOffset, yPos);
                    if (!riverEastWest)
                    {
                        pos = TilePos2(pos.y, pos.x);
                    }

                    if (!validCoords(pos))
                    {
                        // We might meander back to a valid position later,
                        // so we're only breaking out of the inner loop.
                        break;
                    }

                    if (riverbankWidth > 0 && xOffset < riverbankWidth)
                    {
                        // Western riverbank (high to low)
                        auto bankPos = riverbankWidth - xOffset;
                        auto bankHeight = heightMap[pos] * bankPos / riverbankWidth;
                        heightMap[pos] = std::max<uint8_t>(riverbedHeight, bankHeight);
                    }
                    else if (riverbankWidth > 0 && xOffset > easternBankOffset)
                    {
                        // Eastern riverbank (low to high)
                        auto bankPos = xOffset - easternBankOffset;
                        auto bankHeight = heightMap[pos] * bankPos / riverbankWidth;
                        heightMap[pos] = std::max<uint8_t>(riverbedHeight, bankHeight);
                    }
                    else
                    {
                        // Simply carve out the river
                        heightMap[pos] = riverbedHeight;
                    }
                }

                // Let the river meander slightly
                const auto meanderRate = options.riverMeanderRate;
                if (meanderRate > 0 && yPos % 4 == 0)
                {