tests/unit/run_site_baker_tests.gd

@@ -8,7 +8,7 @@ const SiteTerrainData = preload("res://game/domain/sites/site_terrain_data.gd")
 
 const ZONE1_TERRAIN_PATH := "res://content/sites/zone1_vigilant_terrain.res"
 
-const TEST_COUNT := 36
+const TEST_COUNT := 40
 
 var _failures: Array[String] = []
 
@@ -22,6 +22,7 @@ func _init() -> void:
 	_test_escarpment()
 	_test_outcrop()
 	_test_boulder_field()
+	_test_strata()
 
 	if _failures.is_empty():
 		print("Site baker unit tests: %d passed, 0 failed." % TEST_COUNT)
@@ -174,6 +175,43 @@ func _test_boulder_field() -> void:
 	_expect(stacked.elevation_delta(0.0, 0.0) <= 4.0 + 0.001, "overlapping boulders combine by maximum, not by sum")
 
 
+func _test_strata() -> void:
+	# A 45 degree plane sampled every 0.5 m: four cells per 2 m layer.
+	var recipe := _small_recipe()
+	recipe.columns = 41
+	recipe.rows = 41
+	recipe.cell_size_m = 0.5
+	recipe.origin_x_m = -10.0
+	recipe.origin_z_m = -10.0
+	recipe.primitives.append(SiteTerrainBaker.SlopedPlane.new(30.0, 1.0, 0.0, 0.0, 0.0))
+	var plain := SiteTerrainBaker.bake(recipe)
+	recipe.modifiers.append(SiteTerrainBaker.Strata.new(2.0, 0.9, 20.0, 35.0, Vector2.ZERO, 0.0))
+	var terraced := SiteTerrainBaker.bake(recipe)
+	var flat_cells := 0
+	var riser_cells := 0
+	for column in range(5, 35):
+		var rise := terraced.elevations_m[terraced.index_of(column + 1, 20)] - terraced.elevations_m[terraced.index_of(column, 20)]
+		if rise < 0.1:
+			flat_cells += 1
+		elif rise > 0.9:
+			riser_cells += 1
+	_expect(flat_cells >= 8 and riser_cells >= 4, "strata turn a steep slope into ledges and risers (%d flat, %d risers)" % [flat_cells, riser_cells])
+	_expect(is_equal_approx(terraced.elevations_m[terraced.index_of(20, 20)], plain.elevations_m[plain.index_of(20, 20)]), "strata keep the layer boundaries where they were")
+
+	var flat := _small_recipe()
+	flat.primitives.append(SiteTerrainBaker.SlopedPlane.new(30.3, 0.0, 0.0, 0.0, 0.0))
+	flat.modifiers.append(SiteTerrainBaker.Strata.new(2.0, 0.9, 20.0, 35.0, Vector2.ZERO, 0.0))
+	var flat_data := SiteTerrainBaker.bake(flat)
+	_expect(is_equal_approx(flat_data.elevations_m[flat_data.index_of(10, 10)], -30.3), "strata leave flat ground alone")
+
+	var identity := _small_recipe()
+	identity.primitives.append(SiteTerrainBaker.SlopedPlane.new(30.0, 1.0, 0.0, 0.0, 0.0))
+	var before := SiteTerrainBaker.bake(identity)
+	identity.modifiers.append(SiteTerrainBaker.Strata.new(2.0, 0.0, 20.0, 35.0, Vector2.ZERO, 0.0))
+	var after := SiteTerrainBaker.bake(identity)
+	_expect(before.elevations_m == after.elevations_m, "sharpness 0 is the identity")
+
+
 func _test_zone1_artefact_is_stable() -> void:
 	var versioned := load(ZONE1_TERRAIN_PATH) as SiteTerrainData
 	_expect(versioned != null, "versioned zone 1 terrain loads")

tools/site_terrain_baker.gd

@@ -415,6 +415,45 @@ class Modifier extends RefCounted:
 		return elevation_m
 
 
+## Quantises steep ground into horizontal ledges layer_height_m apart: the stratified
+## walls of a canyon or cliff. Flat floors and summits are below minimum_slope_degrees and
+## stay untouched; the effect is full from full_slope_degrees. sharpness 0 leaves the
+## field unchanged, 1 cuts hard steps. radius_m 0 applies everywhere.
+class Strata extends Modifier:
+	var layer_height_m: float
+	var sharpness: float
+	var centre: Vector2
+	var radius_m: float
+	var _minimum_tangent: float
+	var _full_tangent: float
+
+	func _init(
+		p_layer_height_m: float,
+		p_sharpness: float,
+		p_minimum_slope_degrees: float,
+		p_full_slope_degrees: float,
+		p_centre: Vector2,
+		p_radius_m: float
+	) -> void:
+		layer_height_m = p_layer_height_m
+		sharpness = clampf(p_sharpness, 0.0, 0.999)
+		centre = p_centre
+		radius_m = p_radius_m
+		_minimum_tangent = tan(deg_to_rad(p_minimum_slope_degrees))
+		_full_tangent = tan(deg_to_rad(p_full_slope_degrees))
+
+	func modify(x_m: float, z_m: float, elevation_m: float, gradient: Vector2) -> float:
+		var weight := smoothstep(_minimum_tangent, _full_tangent, gradient.length())
+		if radius_m > 0.0:
+			weight *= 1.0 - smoothstep(radius_m * 0.8, radius_m, Vector2(x_m, z_m).distance_to(centre))
+		if weight <= 0.0:
+			return elevation_m
+		var layer := floorf(elevation_m / layer_height_m)
+		var fraction := elevation_m / layer_height_m - layer
+		var sharpened := clampf((fraction - 0.5) / (1.0 - sharpness) + 0.5, 0.0, 1.0)
+		return lerpf(elevation_m, (layer + sharpened) * layer_height_m, weight)
+
+
 class MaterialPatch extends RefCounted:
 	var centre: Vector2
 	var radius_m: float