Pin biome fitness against vanilla runtime

internal/worldgen/biome.go

@@ -4,7 +4,7 @@ import "math"
 
 // This file reproduces net.minecraft.world.level.biome.Climate, the multi-noise
 // biome selector. A point in climate space is six quantized coordinates
-// (temperature, humidity, continentalness, erosion, weirdness, depth); the
+// (temperature, humidity, continentalness, erosion, depth, weirdness); the
 // finder returns the biome whose parameter range is closest to the point by the
 // vanilla fitDistance metric.
 //
@@ -23,13 +23,13 @@ func quantize(v float64) int64 {
 func Quantize(v float64) int64 { return quantize(v) }
 
 // AxisCount is the number of climate coordinates (temperature, humidity,
-// continentalness, erosion, weirdness, depth).
+// continentalness, erosion, depth, weirdness).
 const AxisCount = 6
 
 // TargetPoint is a fully-specified climate point: the value the biome finder
 // tries to match against parameter ranges. Fields are pre-quantized longs.
 type TargetPoint struct {
-	Temperature, Humidity, Continentalness, Erosion, Weirdness, Depth int64
+	Temperature, Humidity, Continentalness, Erosion, Depth, Weirdness int64
 }
 
 // NewTargetPoint quantizes six float climate coordinates into a TargetPoint.
@@ -39,15 +39,15 @@ func NewTargetPoint(temp, humid, cont, ero, weird, depth float64) TargetPoint {
 		Humidity:        quantize(humid),
 		Continentalness: quantize(cont),
 		Erosion:         quantize(ero),
-		Weirdness:       quantize(weird),
 		Depth:           quantize(depth),
+		Weirdness:       quantize(weird),
 	}
 }
 
 // fitDistance is the vanilla distance from a point to a parameter range. A
 // coordinate inside a range contributes zero; offset is applied separately.
 func fitDistance(point TargetPoint, ranges [AxisCount]ClimateRange, offset int64) int64 {
-	values := [AxisCount]int64{point.Temperature, point.Humidity, point.Continentalness, point.Erosion, point.Weirdness, point.Depth}
+	values := [AxisCount]int64{point.Temperature, point.Humidity, point.Continentalness, point.Erosion, point.Depth, point.Weirdness}
 	var total int64
 	for i, value := range values {
 		r := ranges[i]
@@ -73,7 +73,7 @@ func (r ClimateRange) contains(v int64) bool { return v >= r.Min && v <= r.Max }
 // BiomeParameter is one biome entry's full climate signature plus its name.
 type BiomeParameter struct {
 	Name string
-	// ranges[0..5] = temperature, humidity, continentalness, erosion, weirdness, depth.
+	// ranges[0..5] = temperature, humidity, continentalness, erosion, depth, weirdness.
 	Ranges [AxisCount]ClimateRange
 	Offset int64
 }
@@ -118,6 +118,6 @@ func containsAll(ranges [AxisCount]ClimateRange, p TargetPoint) bool {
 		ranges[1].contains(p.Humidity) &&
 		ranges[2].contains(p.Continentalness) &&
 		ranges[3].contains(p.Erosion) &&
-		ranges[4].contains(p.Weirdness) &&
-		ranges[5].contains(p.Depth)
+		ranges[4].contains(p.Depth) &&
+		ranges[5].contains(p.Weirdness)
 }

internal/worldgen/biome_test.go

@@ -48,6 +48,32 @@ func TestParameterTableDistanceOffsetAndTies(t *testing.T) {
 	}
 }
 
+func TestFitnessVectorsAgainstVanillaRuntime(t *testing.T) {
+	zero := [AxisCount]ClimateRange{}
+	temperatureRange := zero
+	temperatureRange[0] = ClimateRange{Min: 0, Max: 10}
+	depthWeirdness := zero
+	depthWeirdness[4] = ClimateRange{Min: 20, Max: 20}
+	depthWeirdness[5] = ClimateRange{Min: 30, Max: 30}
+	for _, vector := range []struct {
+		name   string
+		point  TargetPoint
+		ranges [AxisCount]ClimateRange
+		offset int64
+		want   int64
+	}{
+		{"inside", TargetPoint{Temperature: 5}, temperatureRange, 0, 0},
+		{"below", TargetPoint{Temperature: -3}, temperatureRange, 0, 9},
+		{"above", TargetPoint{Temperature: 14}, temperatureRange, 0, 16},
+		{"offset", TargetPoint{Temperature: 5}, temperatureRange, 7, 49},
+		{"depth-weirdness-order", TargetPoint{Depth: 23, Weirdness: 35}, depthWeirdness, 0, 34},
+	} {
+		if got := fitDistance(vector.point, vector.ranges, vector.offset); got != vector.want {
+			t.Errorf("%s fitness = %d, want vanilla runtime %d", vector.name, got, vector.want)
+		}
+	}
+}
+
 // TestFitDistanceZero confirms identical points are zero-distance and distinct
 // points are positive; the exact value is not asserted to stay robust to
 // representation choices.
@@ -78,6 +104,21 @@ func TestRangeContains(t *testing.T) {
 	}
 }
 
+func TestContainsAllUsesVanillaAxisOrder(t *testing.T) {
+	var ranges [AxisCount]ClimateRange
+	for i := range ranges {
+		ranges[i] = ClimateRange{Min: 0, Max: 0}
+	}
+	ranges[4] = ClimateRange{Min: 20, Max: 20}
+	ranges[5] = ClimateRange{Min: 30, Max: 30}
+	if !containsAll(ranges, TargetPoint{Depth: 20, Weirdness: 30}) {
+		t.Fatal("depth/weirdness ranges were not matched in vanilla order")
+	}
+	if containsAll(ranges, TargetPoint{Depth: 30, Weirdness: 20}) {
+		t.Fatal("accepted swapped depth/weirdness axes")
+	}
+}
+
 // TestSampleColumnDeterministic verifies the same seed/coords give the same
 // biome and a different seed gives (almost certainly) a different one.
 func TestSampleColumnDeterministic(t *testing.T) {