# Copyright © 2020 Hugo Locurcio and contributors - MIT License
# See `LICENSE.md` included in the source distribution for details.
@icon("res://addons/lod/lod_particles.svg")
class_name LODParticles
extends GPUParticles3D

# If `false`, LOD won't update anymore. This can be used for performance comparison
# purposes.
@export var enable_lod := true

# The maximum particle emitting distance in units. Past this distance, particles will no longer emit.
@export var max_emit_distance := 50 # (float, 0.0, 1000.0, 0.1)

# The rate at which LODs will be updated (in seconds). Lower values are more reactive
# but use more CPU, which is especially noticeable with large amounts of LOD-enabled nodes.
# Set this accordingly depending on your camera movement speed.
# The default value should suit most projects already.
# Note: Slow cameras don't need to have LOD-enabled objects update their status often.
# This can overridden by setting the project setting `lod/refresh_rate`.
var refresh_rate := 0.25

# The LOD bias in units.
# Positive values will decrease the detail level and improve performance.
# Negative values will improve visual appearance at the cost of performance.
# This can overridden by setting the project setting `lod/bias`.
var lod_distance_bias := 0.0

# The internal refresh timer.
var timer := 0.0


func _ready() -> void:
	if ProjectSettings.has_setting("lod/particle_bias"):
		lod_distance_bias = ProjectSettings.get_setting("lod/particle_bias")
	if ProjectSettings.has_setting("lod/refresh_rate"):
		refresh_rate = ProjectSettings.get_setting("lod/refresh_rate")

	# Add random jitter to the timer to ensure LODs don't all swap at the same time.
	randomize()
	timer += randf_range(0, refresh_rate)

# Despite LOD not being related to physics, we chose to run in `_physics_process()`
# to minimize the amount of method calls per second (and therefore decrease CPU usage).
func _physics_process(delta: float) -> void:
	if not enable_lod:
		return

	# We need a camera to do the rest.
	var camera := get_viewport().get_camera_3d()
	if camera == null:
		return

	if timer <= refresh_rate:
		timer += delta
		return

	timer = 0.0

	var distance := camera.global_transform.origin.distance_to(global_transform.origin) + lod_distance_bias
	emitting = distance < max_emit_distance