feat(sites): typed terrain data and height field sampler

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

game/domain/sites/site_terrain_data.gd

@@ -0,0 +1,44 @@
+class_name SiteTerrainData
+extends Resource
+
+const SonarMaterial = preload("res://game/domain/sonar/sonar_material.gd")
+
+## Regular single-surface heightfield. Column grows with world +X (east),
+## row grows with world +Z (south). Elevations are world Y in metres.
+@export var columns: int = 0
+@export var rows: int = 0
+@export var cell_size_m: float = 1.0
+@export var origin_x_m: float = 0.0
+@export var origin_z_m: float = 0.0
+@export var elevations_m := PackedFloat32Array()
+@export var materials := PackedByteArray()
+@export var rock_reflectivity: float = 0.72
+@export var sand_reflectivity: float = 0.45
+
+
+func index_of(column: int, row: int) -> int:
+	return row * columns + column
+
+
+func validation_error() -> String:
+	if columns < 2 or rows < 2:
+		return "terrain needs at least 2 columns and 2 rows"
+	if not is_finite(cell_size_m) or cell_size_m <= 0.0:
+		return "terrain cell size must be positive"
+	if not is_finite(origin_x_m) or not is_finite(origin_z_m):
+		return "terrain origin must be finite"
+	var cell_count := columns * rows
+	if elevations_m.size() != cell_count:
+		return "terrain elevation count does not match the grid"
+	if materials.size() != cell_count:
+		return "terrain material count does not match the grid"
+	for elevation: float in elevations_m:
+		if not is_finite(elevation):
+			return "terrain elevations must be finite"
+	for material: int in materials:
+		if not SonarMaterial.is_terrain(material):
+			return "terrain materials must be rock or sand"
+	for reflectivity: float in [rock_reflectivity, sand_reflectivity]:
+		if not is_finite(reflectivity) or reflectivity <= 0.0 or reflectivity > 1.0:
+			return "terrain reflectivity must be within ]0, 1]"
+	return ""

game/domain/sites/terrain_height_field.gd

@@ -0,0 +1,133 @@
+class_name TerrainHeightField
+extends RefCounted
+
+const SonarMaterial = preload("res://game/domain/sonar/sonar_material.gd")
+const SiteTerrainData = preload("res://game/domain/sites/site_terrain_data.gd")
+
+var _data: SiteTerrainData
+var _minimum_elevation_m := 0.0
+var _maximum_elevation_m := 0.0
+
+
+static func from_data(data: SiteTerrainData) -> TerrainHeightField:
+	if data == null or not data.validation_error().is_empty():
+		return null
+	var field := TerrainHeightField.new()
+	field._data = data
+	field._minimum_elevation_m = data.elevations_m[0]
+	field._maximum_elevation_m = data.elevations_m[0]
+	for elevation: float in data.elevations_m:
+		field._minimum_elevation_m = minf(field._minimum_elevation_m, elevation)
+		field._maximum_elevation_m = maxf(field._maximum_elevation_m, elevation)
+	return field
+
+
+func columns() -> int:
+	return _data.columns
+
+
+func rows() -> int:
+	return _data.rows
+
+
+func cell_size_m() -> float:
+	return _data.cell_size_m
+
+
+func origin_m() -> Vector2:
+	return Vector2(_data.origin_x_m, _data.origin_z_m)
+
+
+func bounds_m() -> Rect2:
+	return Rect2(
+		_data.origin_x_m,
+		_data.origin_z_m,
+		float(_data.columns - 1) * _data.cell_size_m,
+		float(_data.rows - 1) * _data.cell_size_m
+	)
+
+
+func contains(x_m: float, z_m: float) -> bool:
+	return bounds_m().has_point(Vector2(x_m, z_m))
+
+
+func minimum_elevation_m() -> float:
+	return _minimum_elevation_m
+
+
+func maximum_elevation_m() -> float:
+	return _maximum_elevation_m
+
+
+func elevation_at_cell(column: int, row: int) -> float:
+	return _data.elevations_m[_data.index_of(_clamp_column(column), _clamp_row(row))]
+
+
+func material_at_cell(column: int, row: int) -> int:
+	return _data.materials[_data.index_of(_clamp_column(column), _clamp_row(row))]
+
+
+func cell_world_position(column: int, row: int) -> Vector3:
+	return Vector3(
+		_data.origin_x_m + float(column) * _data.cell_size_m,
+		elevation_at_cell(column, row),
+		_data.origin_z_m + float(row) * _data.cell_size_m
+	)
+
+
+func normal_at_cell(column: int, row: int) -> Vector3:
+	var left := elevation_at_cell(column - 1, row)
+	var right := elevation_at_cell(column + 1, row)
+	var north := elevation_at_cell(column, row - 1)
+	var south := elevation_at_cell(column, row + 1)
+	var span_x := float(_clamp_column(column + 1) - _clamp_column(column - 1)) * _data.cell_size_m
+	var span_z := float(_clamp_row(row + 1) - _clamp_row(row - 1)) * _data.cell_size_m
+	var slope_x := (right - left) / span_x
+	var slope_z := (south - north) / span_z
+	return Vector3(-slope_x, 1.0, -slope_z).normalized()
+
+
+func elevation_at(x_m: float, z_m: float) -> float:
+	var column_f := clampf(
+		(x_m - _data.origin_x_m) / _data.cell_size_m,
+		0.0,
+		float(_data.columns - 1)
+	)
+	var row_f := clampf(
+		(z_m - _data.origin_z_m) / _data.cell_size_m,
+		0.0,
+		float(_data.rows - 1)
+	)
+	var column := mini(int(floorf(column_f)), _data.columns - 2)
+	var row := mini(int(floorf(row_f)), _data.rows - 2)
+	var tx := column_f - float(column)
+	var tz := row_f - float(row)
+	var top := lerpf(elevation_at_cell(column, row), elevation_at_cell(column + 1, row), tx)
+	var bottom := lerpf(
+		elevation_at_cell(column, row + 1),
+		elevation_at_cell(column + 1, row + 1),
+		tx
+	)
+	return lerpf(top, bottom, tz)
+
+
+func material_at(x_m: float, z_m: float) -> int:
+	var column := int(roundf((x_m - _data.origin_x_m) / _data.cell_size_m))
+	var row := int(roundf((z_m - _data.origin_z_m) / _data.cell_size_m))
+	return material_at_cell(column, row)
+
+
+func reflectivity_for(material: int) -> float:
+	match material:
+		SonarMaterial.Value.SAND:
+			return _data.sand_reflectivity
+		_:
+			return _data.rock_reflectivity
+
+
+func _clamp_column(column: int) -> int:
+	return clampi(column, 0, _data.columns - 1)
+
+
+func _clamp_row(row: int) -> int:
+	return clampi(row, 0, _data.rows - 1)