islaApocalypse/Core/Scripts/BiomePalette.cs

using Godot;

namespace IslaApocalypse.Core
{
	public static class BiomePalette
	{
		/// <summary>
		/// Determines the exact Block ID for a specific voxel in the 3D world based on its depth and biome.
		/// </summary>
		/// <param name="biome">The 2D biome pixel from the MapData.</param>
		/// <param name="surfaceHeight">The maximum height of the terrain at this X/Z coordinate.</param>
		/// <param name="currentY">The Y coordinate of the specific voxel we are painting.</param>
		/// <param name="isRoad">Is this coordinate part of the highway/branch road network?</param>
		public static byte GetVoxelID(Biome biome, int surfaceHeight, int currentY, bool isRoad)
		{
			// 1. Air Check: If we are above the terrain, it's Air.
			if (currentY > surfaceHeight) return BlockRegistry.AIR;

			// 2. Bedrock Check: The very bottom of the world is indestructible.
			if (currentY == 0) return BlockRegistry.BEDROCK;

			// 3. Infrastructure Check: If this is a road, and we are exactly on the surface, paint asphalt.
			if (isRoad && currentY == surfaceHeight) return BlockRegistry.ASPHALT;

			int depthBelowSurface = surfaceHeight - currentY;

			// 4. Subsurface Logic (Dirt layer vs Stone layer)
			// The top 4 blocks are usually dirt/sand, everything below that is solid stone.
			if (depthBelowSurface > 4) return BlockRegistry.STONE;

			// 5. Surface & Shallow Subsurface Logic (Based on Biome)
			switch (biome)
			{
				case Biome.Beach:
				case Biome.Crater:
					return BlockRegistry.SAND; // Craters and Beaches are deep sand

				case Biome.Snow:
				case Biome.Mountain:
					if (depthBelowSurface == 0) return BlockRegistry.SNOW; // Only the top layer is snow
					return BlockRegistry.STONE; // Mountains have shallow topsoil, mostly stone

				case Biome.Wasteland:
					return BlockRegistry.WASTELAND_DIRT;

				case Biome.Jungle:
					if (depthBelowSurface == 0) return BlockRegistry.GRASS_JUNGLE;
					return BlockRegistry.DIRT;

				case Biome.Paradise:
					if (depthBelowSurface == 0) return BlockRegistry.GRASS_PARADISE;
					return BlockRegistry.DIRT;

				case Biome.Tropical:
					if (depthBelowSurface == 0) return BlockRegistry.GRASS_TROPICAL;
					return BlockRegistry.DIRT;

				default:
					return BlockRegistry.DIRT; // Fallback
			}
		}

		// ===================================================================
		// SOFT-FADE COLOURING (rendering only)
		// ===================================================================
		// GetVoxelID above is the authoritative, INTEGER classification. It
		// still decides what block is actually stored in each voxel, and it is
		// deliberately left exactly as it was.
		//
		// What follows answers the same question — "what material is here?" —
		// but for the RENDERER, and it does it differently in two ways:
		//   1. It measures depth as a real number from the true surface height,
		//      instead of counting whole blocks down from a rounded one.
		//   2. Instead of returning one material, it returns the two materials
		//      either side of the nearest boundary plus how far between them we
		//      are, so the renderer can fade rather than snap.
		// That is the whole fix for the horizontal colour banding.

		// Thickness of the top "skin" layer. Mirrors GetVoxelID's rule that
		// only the single topmost block gets grass/snow/asphalt.
		private const float SKIN_DEPTH_METERS = 1.0f;

		// Depth at which we are into solid stone. Mirrors "depthBelowSurface > 4".
		private const float STONE_DEPTH_METERS = 4.0f;

		/// <summary>
		/// Picks the two materials to fade between for a point sitting
		/// <paramref name="depthBelowSurface"/> metres under the real surface.
		/// </summary>
		/// <param name="blendBand">Metres over which one material becomes the next. 0 = hard switch.</param>
		/// <param name="idNear">The material on the shallower side of the boundary.</param>
		/// <param name="idFar">The material on the deeper side.</param>
		/// <param name="blend">0 = fully idNear, 1 = fully idFar.</param>
		public static void GetBlendedVoxelIDs(Biome biome, bool isRoad, float depthBelowSurface,
			float blendBand, out byte idNear, out byte idFar, out float blend)
		{
			// Above the surface can happen by a hair on interpolated vertices; treat as surface.
			float depth = Mathf.Max(depthBelowSurface, 0.0f);

			byte skinID = GetSkinMaterial(biome, isRoad);
			byte shallowID = GetShallowMaterial(biome);

			// Two boundaries exist: skin->shallow and shallow->stone. Work out
			// which one we are closest to and fade across that one.
			if (depth < (SKIN_DEPTH_METERS + STONE_DEPTH_METERS) * 0.5f)
			{
				idNear = skinID;
				idFar = shallowID;
				blend = Fade(depth, SKIN_DEPTH_METERS, blendBand);
			}
			else
			{
				idNear = shallowID;
				idFar = BlockRegistry.STONE;
				blend = Fade(depth, STONE_DEPTH_METERS, blendBand);
			}
		}

		/// <summary>
		/// 0 before the boundary, 1 after it, smoothly eased across a band of
		/// <paramref name="band"/> metres centred on the boundary.
		/// </summary>
		private static float Fade(float depth, float boundary, float band)
		{
			// A band of zero means "behave exactly like the old hard switch".
			if (band <= 0.0f) return depth < boundary ? 0.0f : 1.0f;

			float t = Mathf.Clamp((depth - (boundary - band * 0.5f)) / band, 0.0f, 1.0f);
			return t * t * (3.0f - 2.0f * t); // smoothstep — eases in and out
		}

		/// <summary>The topmost material: what you actually walk on.</summary>
		private static byte GetSkinMaterial(Biome biome, bool isRoad)
		{
			if (isRoad) return BlockRegistry.ASPHALT;

			switch (biome)
			{
				case Biome.Beach:
				case Biome.Crater:    return BlockRegistry.SAND;
				case Biome.Snow:
				case Biome.Mountain:  return BlockRegistry.SNOW;
				case Biome.Wasteland: return BlockRegistry.WASTELAND_DIRT;
				case Biome.Jungle:    return BlockRegistry.GRASS_JUNGLE;
				case Biome.Paradise:  return BlockRegistry.GRASS_PARADISE;
				case Biome.Tropical:  return BlockRegistry.GRASS_TROPICAL;
				default:              return BlockRegistry.DIRT;
			}
		}

		/// <summary>The layer just underneath the skin, before stone takes over.</summary>
		private static byte GetShallowMaterial(Biome biome)
		{
			switch (biome)
			{
				// Sand goes all the way down on beaches and in the crater.
				case Biome.Beach:
				case Biome.Crater:    return BlockRegistry.SAND;

				// Mountains have essentially no topsoil — straight to rock.
				case Biome.Snow:
				case Biome.Mountain:  return BlockRegistry.STONE;

				case Biome.Wasteland: return BlockRegistry.WASTELAND_DIRT;
				default:              return BlockRegistry.DIRT;
			}
		}
	}
}