Adds mineshaft support for ancient versions of Minecraft

(v1.3.2 all the way back to when mineshafts were first introduced)

src/amidst/map/layers/MineshaftLayer.java

@@ -13,17 +13,25 @@ public class MineshaftLayer extends IconLayer {
 	private final static double chancePerChunk_v1_7 = 0.004D;
 	private final static double chancePerChunk_v1_6 = 0.01D;
 
-	private Random random = new Random();
-	private double chancePerChunk;
+	private Random  random = new Random();
+	private double  chancePerChunk;
+	private boolean useOriginalAlogirithm = false;
 
 	public MineshaftLayer() {
 
-		if (MinecraftUtil.getVersion().isAtLeast(VersionInfo.V1_7_2)) {
-			// Mineshafts became less common from version 1.7.2 onward 
-			chancePerChunk = chancePerChunk_v1_7;			
+		if (MinecraftUtil.getVersion().isAtLeast(VersionInfo.V1_4_2)) {
+			// Use the current mineshaft algorithm
+
+			if (MinecraftUtil.getVersion().isAtLeast(VersionInfo.V1_7_2)) {
+				// Mineshafts became less common from version 1.7.2 onward 
+				chancePerChunk = chancePerChunk_v1_7;			
+			} else {
+				chancePerChunk = chancePerChunk_v1_6;			
+			}
 		} else {
-			chancePerChunk = chancePerChunk_v1_6;			
-		}		
+			// Use the original mineshaft algorithm (retired in v1.4.2).
+			useOriginalAlogirithm = true;
+		}
 	}
 
 	@Override
@@ -33,26 +41,18 @@ public boolean isVisible() {
 	@Override
 	public void generateMapObjects(Fragment frag) {
 
-		if (MinecraftVersionIsSupported()) {
-
-			int size = Fragment.SIZE >> 4;
-			for (int x = 0; x < size; x++) {
-				for (int y = 0; y < size; y++) {
-					int chunkX = x + frag.getChunkX();
-					int chunkY = y + frag.getChunkY();
-					if (checkChunk(chunkX, chunkY)) {
-						frag.addObject(new MapObjectMineshaft((x << 4) + 8, (y << 4) + 8).setParent(this));
-					}
+		int size = Fragment.SIZE >> 4;
+		for (int x = 0; x < size; x++) {
+			for (int y = 0; y < size; y++) {
+				int chunkX = x + frag.getChunkX();
+				int chunkY = y + frag.getChunkY();
+				if (checkChunk(chunkX, chunkY)) {
+					frag.addObject(new MapObjectMineshaft((x << 4) + 8, (y << 4) + 8).setParent(this));
 				}
 			}
 		}
 	}
 
-	/** @return true if Minecraft is v1.4.2 or greater (earlier versions place mineshafts differently) */
-	public static boolean MinecraftVersionIsSupported() {
-		return MinecraftUtil.getVersion().isAtLeast(VersionInfo.V1_4_2);
-	}
-
 	public boolean checkChunk(int chunkX, int chunkY) {
         random.setSeed(Options.instance.seed);
         long var7 = random.nextLong();
@@ -63,6 +63,22 @@ public boolean checkChunk(int chunkX, int chunkY) {
 		random.setSeed(var13 ^ var15 ^ Options.instance.seed);
 		random.nextInt();
 
-		return (random.nextDouble() < chancePerChunk) && random.nextInt(80) < Math.max(Math.abs(chunkX), Math.abs(chunkY));
+		if (useOriginalAlogirithm) {
+			// Empirical testing suggests this version of the algorithm works all the way back to b1.8,  
+			// and the Minecraft Wiki says b1.8 was when mineshafts were introduced, but since Amidst 
+			// versions only go back as far as VersionInfo.Vbeta_1_8_1 I won't bother to check for 
+			// pre-mineshaft versions.
+			//
+			// I've not decompiled the very early Minecraft versions, and TheMasterCaver points out that "for older 
+			// versions it is possible that the second part of this code, nextInt(80) < (max of absolute value 
+			// of chunk coordinates), may not have been present, resulting in mineshafts being equally as common 
+			// near the origin as they currently are 80 or more chunks away."
+			// I've included TheMasterCaver's comment because my empirical testing that Amidst mineshafts do 
+			// appear in the game can't tell us whether the very early versions have fewer mineshafts near the origin. 
+			return (random.nextInt(100) == 0) && (random.nextInt(80) < Math.max(Math.abs(chunkX), Math.abs(chunkY)));
+		} else {
+			// As of v1.4.2 Minecraft switched to this version of the algorithm
+			return (random.nextDouble() < chancePerChunk) && random.nextInt(80) < Math.max(Math.abs(chunkX), Math.abs(chunkY));
+		}
 	}
 }

src/amidst/version/VersionInfo.java

@@ -55,7 +55,7 @@ public enum VersionInfo {
 	V1_9pre3("to"),
 	V1_9pre2("sv"),
 	V1_9pre1("sq"),
-	Vbeta_1_8_1("[Bhwqpyrrviqswdbzdqurkhqrgviwbomnabjrxmafvoeacfer[J[Jaddmkbb"); // Had to rename from V1_8_1 - should it just be removed?
+	Vbeta_1_8_1("[Bhwqpyrrviqswdbzdqurkhqrgviwbomnabjrxmafvoeacfer[J[Jaddmkbb"); // Includes b1.8 (had to rename this enum from V1_8_1)
 
 	public final String versionId;