Rename GPUParticles2D/3D's `trail_length_secs` to `trail_lifetime`

The property already has a "seconds" suffix in the inspector.
The "lifetime" term makes it more obvious that the property is
specified as time, not a distance in units.

The property hint now allows manually entering values greater than
10 seconds.

The internal rendering value's default now matches the particles
nodes' default.

8 files changed, 39 insertions, 30 deletions

diff --git a/doc/classes/GPUParticles2D.xml b/doc/classes/GPUParticles2D.xml
index 4916171900..c7d10078e8 100644
--- a/doc/classes/GPUParticles2D.xml
+++ b/doc/classes/GPUParticles2D.xml
@@ -89,12 +89,17 @@
 			Particle texture. If [code]null[/code], particles will be squares.
 		</member>
 		<member name="trail_enabled" type="bool" setter="set_trail_enabled" getter="is_trail_enabled" default="false">
+			If [code]true[/code], enables particle trails using a mesh skinning system.
+			[b]Note:[/b] Unlike [GPUParticles3D], the number of trail sections and subdivisions is set with the [member trail_sections] and [member trail_section_subdivisions] properties.
 		</member>
-		<member name="trail_length_secs" type="float" setter="set_trail_length" getter="get_trail_length" default="0.3">
+		<member name="trail_lifetime" type="float" setter="set_trail_lifetime" getter="get_trail_lifetime" default="0.3">
+			The amount of time the particle's trail should represent (in seconds). Only effective if [member trail_enabled] is [code]true[/code].
 		</member>
 		<member name="trail_section_subdivisions" type="int" setter="set_trail_section_subdivisions" getter="get_trail_section_subdivisions" default="4">
+			The number of subdivisions to use for the particle trail rendering. Higher values can result in smoother trail curves, at the cost of performance due to increased mesh complexity. See also [member trail_sections]. Only effective if [member trail_enabled] is [code]true[/code].
 		</member>
 		<member name="trail_sections" type="int" setter="set_trail_sections" getter="get_trail_sections" default="8">
+			The number of sections to use for the particle trail rendering. Higher values can result in smoother trail curves, at the cost of performance due to increased mesh complexity. See also [member trail_section_subdivisions]. Only effective if [member trail_enabled] is [code]true[/code].
 		</member>
 		<member name="visibility_rect" type="Rect2" setter="set_visibility_rect" getter="get_visibility_rect" default="Rect2(-100, -100, 200, 200)">
 			The [Rect2] that determines the node's region which needs to be visible on screen for the particle system to be active.
diff --git a/doc/classes/GPUParticles3D.xml b/doc/classes/GPUParticles3D.xml
index d0be4d784a..ea53c5b4b5 100644
--- a/doc/classes/GPUParticles3D.xml
+++ b/doc/classes/GPUParticles3D.xml
@@ -116,8 +116,12 @@
 		<member name="sub_emitter" type="NodePath" setter="set_sub_emitter" getter="get_sub_emitter" default="NodePath(&quot;&quot;)">
 		</member>
 		<member name="trail_enabled" type="bool" setter="set_trail_enabled" getter="is_trail_enabled" default="false">
+			If [code]true[/code], enables particle trails using a mesh skinning system. Designed to work with [RibbonTrailMesh] and [TubeTrailMesh].
+			[b]Note:[/b] [member BaseMaterial3D.use_particle_trails] must also be enabled on the particle mesh's material. Otherwise, setting [member trail_enabled] to [code]true[/code] will have no effect.
+			[b]Note:[/b] Unlike [GPUParticles2D], the number of trail sections and subdivisions is set in the [RibbonTrailMesh] or the [TubeTrailMesh]'s properties.
 		</member>
-		<member name="trail_length_secs" type="float" setter="set_trail_length" getter="get_trail_length" default="0.3">
+		<member name="trail_lifetime" type="float" setter="set_trail_lifetime" getter="get_trail_lifetime" default="0.3">
+			The amount of time the particle's trail should represent (in seconds). Only effective if [member trail_enabled] is [code]true[/code].
 		</member>
 		<member name="transform_align" type="int" setter="set_transform_align" getter="get_transform_align" enum="GPUParticles3D.TransformAlign" default="0">
 		</member>
diff --git a/scene/2d/gpu_particles_2d.cpp b/scene/2d/gpu_particles_2d.cpp
index 9786b01058..e18f2bd1a1 100644
--- a/scene/2d/gpu_particles_2d.cpp
+++ b/scene/2d/gpu_particles_2d.cpp
@@ -141,16 +141,16 @@ void GPUParticles2D::set_process_material(const Ref<Material> &p_material) {
 
 void GPUParticles2D::set_trail_enabled(bool p_enabled) {
 	trail_enabled = p_enabled;
-	RS::get_singleton()->particles_set_trails(particles, trail_enabled, trail_length);
+	RS::get_singleton()->particles_set_trails(particles, trail_enabled, trail_lifetime);
 	queue_redraw();
 
 	RS::get_singleton()->particles_set_transform_align(particles, p_enabled ? RS::PARTICLES_TRANSFORM_ALIGN_Y_TO_VELOCITY : RS::PARTICLES_TRANSFORM_ALIGN_DISABLED);
 }
 
-void GPUParticles2D::set_trail_length(double p_seconds) {
+void GPUParticles2D::set_trail_lifetime(double p_seconds) {
 	ERR_FAIL_COND(p_seconds < 0.001);
-	trail_length = p_seconds;
-	RS::get_singleton()->particles_set_trails(particles, trail_enabled, trail_length);
+	trail_lifetime = p_seconds;
+	RS::get_singleton()->particles_set_trails(particles, trail_enabled, trail_lifetime);
 	queue_redraw();
 }
 
@@ -181,8 +181,8 @@ bool GPUParticles2D::is_trail_enabled() const {
 	return trail_enabled;
 }
 
-double GPUParticles2D::get_trail_length() const {
-	return trail_length;
+double GPUParticles2D::get_trail_lifetime() const {
+	return trail_lifetime;
 }
 
 void GPUParticles2D::_update_collision_size() {
@@ -614,10 +614,10 @@ void GPUParticles2D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("emit_particle", "xform", "velocity", "color", "custom", "flags"), &GPUParticles2D::emit_particle);
 
 	ClassDB::bind_method(D_METHOD("set_trail_enabled", "enabled"), &GPUParticles2D::set_trail_enabled);
-	ClassDB::bind_method(D_METHOD("set_trail_length", "secs"), &GPUParticles2D::set_trail_length);
+	ClassDB::bind_method(D_METHOD("set_trail_lifetime", "secs"), &GPUParticles2D::set_trail_lifetime);
 
 	ClassDB::bind_method(D_METHOD("is_trail_enabled"), &GPUParticles2D::is_trail_enabled);
-	ClassDB::bind_method(D_METHOD("get_trail_length"), &GPUParticles2D::get_trail_length);
+	ClassDB::bind_method(D_METHOD("get_trail_lifetime"), &GPUParticles2D::get_trail_lifetime);
 
 	ClassDB::bind_method(D_METHOD("set_trail_sections", "sections"), &GPUParticles2D::set_trail_sections);
 	ClassDB::bind_method(D_METHOD("get_trail_sections"), &GPUParticles2D::get_trail_sections);
@@ -647,7 +647,7 @@ void GPUParticles2D::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "draw_order", PROPERTY_HINT_ENUM, "Index,Lifetime,Reverse Lifetime"), "set_draw_order", "get_draw_order");
 	ADD_GROUP("Trails", "trail_");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "trail_enabled"), "set_trail_enabled", "is_trail_enabled");
-	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "trail_length_secs", PROPERTY_HINT_RANGE, "0.01,10,0.01,suffix:s"), "set_trail_length", "get_trail_length");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "trail_lifetime", PROPERTY_HINT_RANGE, "0.01,10,0.01,or_greater,suffix:s"), "set_trail_lifetime", "get_trail_lifetime");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "trail_sections", PROPERTY_HINT_RANGE, "2,128,1"), "set_trail_sections", "get_trail_sections");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "trail_section_subdivisions", PROPERTY_HINT_RANGE, "1,1024,1"), "set_trail_section_subdivisions", "get_trail_section_subdivisions");
 	ADD_GROUP("Process Material", "process_");
diff --git a/scene/2d/gpu_particles_2d.h b/scene/2d/gpu_particles_2d.h
index d613b4ef51..7fba174357 100644
--- a/scene/2d/gpu_particles_2d.h
+++ b/scene/2d/gpu_particles_2d.h
@@ -74,7 +74,7 @@ private:
 	real_t collision_base_size = 1.0;
 
 	bool trail_enabled = false;
-	double trail_length = 0.3;
+	double trail_lifetime = 0.3;
 	int trail_sections = 8;
 	int trail_section_subdivisions = 4;
 
@@ -104,7 +104,7 @@ public:
 	void set_speed_scale(double p_scale);
 	void set_collision_base_size(real_t p_ratio);
 	void set_trail_enabled(bool p_enabled);
-	void set_trail_length(double p_seconds);
+	void set_trail_lifetime(double p_seconds);
 	void set_trail_sections(int p_sections);
 	void set_trail_section_subdivisions(int p_subdivisions);
 
@@ -126,7 +126,7 @@ public:
 
 	real_t get_collision_base_size() const;
 	bool is_trail_enabled() const;
-	double get_trail_length() const;
+	double get_trail_lifetime() const;
 	int get_trail_sections() const;
 	int get_trail_section_subdivisions() const;
 
diff --git a/scene/3d/gpu_particles_3d.cpp b/scene/3d/gpu_particles_3d.cpp
index dbbf196f7a..9d04202c2d 100644
--- a/scene/3d/gpu_particles_3d.cpp
+++ b/scene/3d/gpu_particles_3d.cpp
@@ -176,22 +176,22 @@ void GPUParticles3D::set_draw_order(DrawOrder p_order) {
 
 void GPUParticles3D::set_trail_enabled(bool p_enabled) {
 	trail_enabled = p_enabled;
-	RS::get_singleton()->particles_set_trails(particles, trail_enabled, trail_length);
+	RS::get_singleton()->particles_set_trails(particles, trail_enabled, trail_lifetime);
 	update_configuration_warnings();
 }
 
-void GPUParticles3D::set_trail_length(double p_seconds) {
+void GPUParticles3D::set_trail_lifetime(double p_seconds) {
 	ERR_FAIL_COND(p_seconds < 0.001);
-	trail_length = p_seconds;
-	RS::get_singleton()->particles_set_trails(particles, trail_enabled, trail_length);
+	trail_lifetime = p_seconds;
+	RS::get_singleton()->particles_set_trails(particles, trail_enabled, trail_lifetime);
 }
 
 bool GPUParticles3D::is_trail_enabled() const {
 	return trail_enabled;
 }
 
-double GPUParticles3D::get_trail_length() const {
-	return trail_length;
+double GPUParticles3D::get_trail_lifetime() const {
+	return trail_lifetime;
 }
 
 GPUParticles3D::DrawOrder GPUParticles3D::get_draw_order() const {
@@ -552,10 +552,10 @@ void GPUParticles3D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("emit_particle", "xform", "velocity", "color", "custom", "flags"), &GPUParticles3D::emit_particle);
 
 	ClassDB::bind_method(D_METHOD("set_trail_enabled", "enabled"), &GPUParticles3D::set_trail_enabled);
-	ClassDB::bind_method(D_METHOD("set_trail_length", "secs"), &GPUParticles3D::set_trail_length);
+	ClassDB::bind_method(D_METHOD("set_trail_lifetime", "secs"), &GPUParticles3D::set_trail_lifetime);
 
 	ClassDB::bind_method(D_METHOD("is_trail_enabled"), &GPUParticles3D::is_trail_enabled);
-	ClassDB::bind_method(D_METHOD("get_trail_length"), &GPUParticles3D::get_trail_length);
+	ClassDB::bind_method(D_METHOD("get_trail_lifetime"), &GPUParticles3D::get_trail_lifetime);
 
 	ClassDB::bind_method(D_METHOD("set_transform_align", "align"), &GPUParticles3D::set_transform_align);
 	ClassDB::bind_method(D_METHOD("get_transform_align"), &GPUParticles3D::get_transform_align);
@@ -583,7 +583,7 @@ void GPUParticles3D::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "transform_align", PROPERTY_HINT_ENUM, "Disabled,Z-Billboard,Y to Velocity,Z-Billboard + Y to Velocity"), "set_transform_align", "get_transform_align");
 	ADD_GROUP("Trails", "trail_");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "trail_enabled"), "set_trail_enabled", "is_trail_enabled");
-	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "trail_length_secs", PROPERTY_HINT_RANGE, "0.01,10,0.01,suffix:s"), "set_trail_length", "get_trail_length");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "trail_lifetime", PROPERTY_HINT_RANGE, "0.01,10,0.01,or_greater,suffix:s"), "set_trail_lifetime", "get_trail_lifetime");
 	ADD_GROUP("Process Material", "");
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "process_material", PROPERTY_HINT_RESOURCE_TYPE, "ShaderMaterial,ParticleProcessMaterial"), "set_process_material", "get_process_material");
 	ADD_GROUP("Draw Passes", "draw_");
@@ -627,7 +627,7 @@ GPUParticles3D::GPUParticles3D() {
 	set_pre_process_time(0);
 	set_explosiveness_ratio(0);
 	set_randomness_ratio(0);
-	set_trail_length(0.3);
+	set_trail_lifetime(0.3);
 	set_visibility_aabb(AABB(Vector3(-4, -4, -4), Vector3(8, 8, 8)));
 	set_use_local_coordinates(false);
 	set_draw_passes(1);
diff --git a/scene/3d/gpu_particles_3d.h b/scene/3d/gpu_particles_3d.h
index ef92218e4d..835d71862a 100644
--- a/scene/3d/gpu_particles_3d.h
+++ b/scene/3d/gpu_particles_3d.h
@@ -76,7 +76,7 @@ private:
 	real_t collision_base_size = 0.01;
 
 	bool trail_enabled = false;
-	double trail_length = 0.3;
+	double trail_lifetime = 0.3;
 
 	TransformAlign transform_align = TRANSFORM_ALIGN_DISABLED;
 
@@ -112,7 +112,7 @@ public:
 	void set_speed_scale(double p_scale);
 	void set_collision_base_size(real_t p_ratio);
 	void set_trail_enabled(bool p_enabled);
-	void set_trail_length(double p_seconds);
+	void set_trail_lifetime(double p_seconds);
 
 	bool is_emitting() const;
 	int get_amount() const;
@@ -127,7 +127,7 @@ public:
 	double get_speed_scale() const;
 	real_t get_collision_base_size() const;
 	bool is_trail_enabled() const;
-	double get_trail_length() const;
+	double get_trail_lifetime() const;
 
 	void set_fixed_fps(int p_count);
 	int get_fixed_fps() const;
diff --git a/servers/rendering/renderer_rd/storage_rd/particles_storage.cpp b/servers/rendering/renderer_rd/storage_rd/particles_storage.cpp
index 7fa0bb64a3..854976692e 100644
--- a/servers/rendering/renderer_rd/storage_rd/particles_storage.cpp
+++ b/servers/rendering/renderer_rd/storage_rd/particles_storage.cpp
@@ -425,7 +425,7 @@ void ParticlesStorage::particles_set_trails(RID p_particles, bool p_enable, doub
 	p_length = MIN(10.0, p_length);
 
 	particles->trails_enabled = p_enable;
-	particles->trail_length = p_length;
+	particles->trail_lifetime = p_length;
 
 	_particles_free_data(particles);
 
@@ -1351,7 +1351,7 @@ void ParticlesStorage::update_particles() {
 			int history_size = 1;
 			int trail_steps = 1;
 			if (particles->trails_enabled && particles->trail_bind_poses.size() > 1) {
-				history_size = MAX(1, int(particles->trail_length * fixed_fps));
+				history_size = MAX(1, int(particles->trail_lifetime * fixed_fps));
 				trail_steps = particles->trail_bind_poses.size();
 			}
 
diff --git a/servers/rendering/renderer_rd/storage_rd/particles_storage.h b/servers/rendering/renderer_rd/storage_rd/particles_storage.h
index 017844626f..6478e2b5dc 100644
--- a/servers/rendering/renderer_rd/storage_rd/particles_storage.h
+++ b/servers/rendering/renderer_rd/storage_rd/particles_storage.h
@@ -232,7 +232,7 @@ private:
 
 		Dependency dependency;
 
-		double trail_length = 1.0;
+		double trail_lifetime = 0.3;
 		bool trails_enabled = false;
 		LocalVector<ParticlesFrameParams> frame_history;
 		LocalVector<ParticlesFrameParams> trail_params;