N-Carter · August 14, 2024 15:02
diff --git a/partial_mesh_update_test.gd b/partial_mesh_update_test.gd
 extends MeshInstance3D


 @export var _grid_size := 2

 # Which of the array of quads to change (must be between 0 and _grid_size * _grid_size):
 @export var _quad_to_change := 1

 var _array_mesh : ArrayMesh


 func _ready() -> void:
 	_array_mesh = ArrayMesh.new()
 	
 	var vertices = PackedVector3Array()
 	
 	# Fill the vertex array with quads arranged in a grid. The quads are made out of two triangles:
 	
 	for y in _grid_size:
 		for x in _grid_size:
 			vertices.append_array(_create_quad_vertices(Vector3(x, y, 0), 0.9))
 	
 	# Just using the vertex array here for simplicity:
 	
 	var arrays = []
 	arrays.resize(Mesh.ARRAY_MAX)
 	arrays[Mesh.ARRAY_VERTEX] = vertices
 	
 	# Calling this function once puts the new surface in index 0, and each subsequent call will
 	# increase the new surface number by one:
 	
 	_array_mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, arrays)
 	mesh = _array_mesh


 func _process(delta: float) -> void:
 	# We're going to randomly change the size of one of the quads every frame.
 	
 	# We have to work out its position again, but that's not part of the example:
 	var quad_origin := Vector3(_quad_to_change % _grid_size, _quad_to_change / _grid_size, 0.0)
 	
 	# Make a new set of vertices for that quad:
 	var new_vertices := _create_quad_vertices(quad_origin,  randf() * 0.5)
 	
 	# Convert it into something which surface_update_vertex_region() will accept:
 	var byte_array := new_vertices.to_byte_array()
 	
 	# We have to pass an offset in byte indices, not in vertex indices. We have 6 vertices per
 	# quad, 3 elements per vertex (x, y, z) and each element is 4 bytes (a float):
 	var byte_offset := 6 * 3 * 4
 	
 	# We're editing surface index 0 because that's the only one we have:
 	_array_mesh.surface_update_vertex_region(0, _quad_to_change * byte_offset, byte_array)


 func _create_quad_vertices(origin : Vector3, scale : float) -> PackedVector3Array:
 	# Create a quad out of two triangles:
 	
 	var vertices = PackedVector3Array()
 	
 	vertices.push_back(origin + Vector3(0.0, 0.0, 0.0) * scale)
 	vertices.push_back(origin + Vector3(0.0, 1.0, 0.0) * scale)
 	vertices.push_back(origin + Vector3(1.0, 1.0, 0.0) * scale)
 	
 	vertices.push_back(origin + Vector3(0.0, 0.0, 0.0) * scale)
 	vertices.push_back(origin + Vector3(1.0, 1.0, 0.0) * scale)
 	vertices.push_back(origin + Vector3(1.0, 0.0, 0.0) * scale)
 	
 	return vertices
	extends MeshInstance3D


	@export var _grid_size := 2

	# Which of the array of quads to change (must be between 0 and _grid_size * _grid_size):
	@export var _quad_to_change := 1

	var _array_mesh : ArrayMesh


	func _ready() -> void:
	_array_mesh = ArrayMesh.new()

	var vertices = PackedVector3Array()

	# Fill the vertex array with quads arranged in a grid. The quads are made out of two triangles:

	for y in _grid_size:
	for x in _grid_size:
	vertices.append_array(_create_quad_vertices(Vector3(x, y, 0), 0.9))

	# Just using the vertex array here for simplicity:

	var arrays = []
	arrays.resize(Mesh.ARRAY_MAX)
	arrays[Mesh.ARRAY_VERTEX] = vertices

	# Calling this function once puts the new surface in index 0, and each subsequent call will
	# increase the new surface number by one:

	_array_mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, arrays)
	mesh = _array_mesh


	func _process(delta: float) -> void:
	# We're going to randomly change the size of one of the quads every frame.

	# We have to work out its position again, but that's not part of the example:
	var quad_origin := Vector3(_quad_to_change % _grid_size, _quad_to_change / _grid_size, 0.0)

	# Make a new set of vertices for that quad:
	var new_vertices := _create_quad_vertices(quad_origin, randf() * 0.5)

	# Convert it into something which surface_update_vertex_region() will accept:
	var byte_array := new_vertices.to_byte_array()

	# We have to pass an offset in byte indices, not in vertex indices. We have 6 vertices per
	# quad, 3 elements per vertex (x, y, z) and each element is 4 bytes (a float):
	var byte_offset := 6 * 3 * 4

	# We're editing surface index 0 because that's the only one we have:
	_array_mesh.surface_update_vertex_region(0, _quad_to_change * byte_offset, byte_array)


	func _create_quad_vertices(origin : Vector3, scale : float) -> PackedVector3Array:
	# Create a quad out of two triangles:

	var vertices = PackedVector3Array()

	vertices.push_back(origin + Vector3(0.0, 0.0, 0.0) * scale)
	vertices.push_back(origin + Vector3(0.0, 1.0, 0.0) * scale)
	vertices.push_back(origin + Vector3(1.0, 1.0, 0.0) * scale)

	vertices.push_back(origin + Vector3(0.0, 0.0, 0.0) * scale)
	vertices.push_back(origin + Vector3(1.0, 1.0, 0.0) * scale)
	vertices.push_back(origin + Vector3(1.0, 0.0, 0.0) * scale)

	return vertices