Add "At Start" mode for sub-emitter particles

doc/classes/ParticleProcessMaterial.xml

@@ -346,6 +346,10 @@
 			The amount of particles to spawn from the subemitter node when the particle expires.
 			[b]Note:[/b] This value shouldn't exceed [member GPUParticles2D.amount] or [member GPUParticles3D.amount] defined on the [i]subemitter node[/i] (not the main node), relative to the subemitter's particle lifetime. If the number of particles is exceeded, no new particles will spawn from the subemitter until enough particles have expired.
 		</member>
+		<member name="sub_emitter_amount_at_start" type="int" setter="set_sub_emitter_amount_at_start" getter="get_sub_emitter_amount_at_start">
+			The amount of particles to spawn from the subemitter node when the particle spawns.
+			[b]Note:[/b] This value shouldn't exceed [member GPUParticles2D.amount] or [member GPUParticles3D.amount] defined on the [i]subemitter node[/i] (not the main node), relative to the subemitter's particle lifetime. If the number of particles is exceeded, no new particles will spawn from the subemitter until enough particles have expired.
+		</member>
 		<member name="sub_emitter_frequency" type="float" setter="set_sub_emitter_frequency" getter="get_sub_emitter_frequency">
 			The frequency at which particles should be emitted from the subemitter node. One particle will be spawned every [member sub_emitter_frequency] seconds.
 			[b]Note:[/b] This value shouldn't exceed [member GPUParticles2D.amount] or [member GPUParticles3D.amount] defined on the [i]subemitter node[/i] (not the main node), relative to the subemitter's particle lifetime. If the number of particles is exceeded, no new particles will spawn from the subemitter until enough particles have expired.
@@ -514,7 +518,9 @@
 		</constant>
 		<constant name="SUB_EMITTER_AT_COLLISION" value="3" enum="SubEmitterMode">
 		</constant>
-		<constant name="SUB_EMITTER_MAX" value="4" enum="SubEmitterMode">
+		<constant name="SUB_EMITTER_AT_START" value="4" enum="SubEmitterMode">
+		</constant>
+		<constant name="SUB_EMITTER_MAX" value="5" enum="SubEmitterMode">
 			Represents the size of the [enum SubEmitterMode] enum.
 		</constant>
 		<constant name="COLLISION_DISABLED" value="0" enum="CollisionMode">

scene/resources/particle_process_material.cpp

@@ -132,6 +132,7 @@ void ParticleProcessMaterial::init_shaders() {
 	shader_names->sub_emitter_frequency = "sub_emitter_frequency";
 	shader_names->sub_emitter_amount_at_end = "sub_emitter_amount_at_end";
 	shader_names->sub_emitter_amount_at_collision = "sub_emitter_amount_at_collision";
+	shader_names->sub_emitter_amount_at_start = "sub_emitter_amount_at_start";
 	shader_names->sub_emitter_keep_velocity = "sub_emitter_keep_velocity";
 
 	shader_names->collision_friction = "collision_friction";
@@ -287,6 +288,9 @@ void ParticleProcessMaterial::_update_shader() {
 		if (sub_emitter_mode == SUB_EMITTER_AT_COLLISION) {
 			code += "uniform int sub_emitter_amount_at_collision;\n";
 		}
+		if (sub_emitter_mode == SUB_EMITTER_AT_START) {
+			code += "uniform int sub_emitter_amount_at_start;\n";
+		}
 		code += "uniform bool sub_emitter_keep_velocity;\n";
 	}
 
@@ -918,6 +922,10 @@ void ParticleProcessMaterial::_update_shader() {
 	code += "	float pi = 3.14159;\n";
 	code += "	float degree_to_rad = pi / 180.0;\n\n";
 
+	if (sub_emitter_mode == SUB_EMITTER_AT_START && !RenderingServer::get_singleton()->is_low_end()) {
+		code += "	bool just_spawned = CUSTOM.y == 0.0;\n";
+	}
+
 	code += "	CUSTOM.y += DELTA / LIFETIME;\n";
 	code += "	CUSTOM.y = mix(CUSTOM.y, 1.0, INTERPOLATE_TO_END);\n";
 	code += "	float lifetime_percent = CUSTOM.y / params.lifetime;\n";
@@ -1134,6 +1142,11 @@ void ParticleProcessMaterial::_update_shader() {
 				code += "		emit_count = sub_emitter_amount_at_end;\n";
 				code += "	}\n";
 			} break;
+			case SUB_EMITTER_AT_START: {
+				code += "	if (just_spawned) {\n";
+				code += "		emit_count = sub_emitter_amount_at_start;\n";
+				code += "	}\n";
+			} break;
 			default: {
 			}
 		}
@@ -1819,6 +1832,10 @@ void ParticleProcessMaterial::_validate_property(PropertyInfo &p_property) const
 		p_property.usage = PROPERTY_USAGE_NONE;
 	}
 
+	if (p_property.name == "sub_emitter_amount_at_start" && sub_emitter_mode != SUB_EMITTER_AT_START) {
+		p_property.usage = PROPERTY_USAGE_NONE;
+	}
+
 	if (!turbulence_enabled) {
 		if (p_property.name == "turbulence_noise_strength" ||
 				p_property.name == "turbulence_noise_scale" ||
@@ -1893,6 +1910,15 @@ int ParticleProcessMaterial::get_sub_emitter_amount_at_collision() const {
 	return sub_emitter_amount_at_collision;
 }
 
+void ParticleProcessMaterial::set_sub_emitter_amount_at_start(int p_amount) {
+	sub_emitter_amount_at_start = p_amount;
+	RenderingServer::get_singleton()->material_set_param(_get_material(), shader_names->sub_emitter_amount_at_start, p_amount);
+}
+
+int ParticleProcessMaterial::get_sub_emitter_amount_at_start() const {
+	return sub_emitter_amount_at_start;
+}
+
 void ParticleProcessMaterial::set_sub_emitter_keep_velocity(bool p_enable) {
 	sub_emitter_keep_velocity = p_enable;
 	RenderingServer::get_singleton()->material_set_param(_get_material(), shader_names->sub_emitter_keep_velocity, p_enable);
@@ -2074,6 +2100,9 @@ void ParticleProcessMaterial::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_sub_emitter_amount_at_collision"), &ParticleProcessMaterial::get_sub_emitter_amount_at_collision);
 	ClassDB::bind_method(D_METHOD("set_sub_emitter_amount_at_collision", "amount"), &ParticleProcessMaterial::set_sub_emitter_amount_at_collision);
 
+	ClassDB::bind_method(D_METHOD("get_sub_emitter_amount_at_start"), &ParticleProcessMaterial::get_sub_emitter_amount_at_start);
+	ClassDB::bind_method(D_METHOD("set_sub_emitter_amount_at_start", "amount"), &ParticleProcessMaterial::set_sub_emitter_amount_at_start);
+
 	ClassDB::bind_method(D_METHOD("get_sub_emitter_keep_velocity"), &ParticleProcessMaterial::get_sub_emitter_keep_velocity);
 	ClassDB::bind_method(D_METHOD("set_sub_emitter_keep_velocity", "enable"), &ParticleProcessMaterial::set_sub_emitter_keep_velocity);
 
@@ -2203,10 +2232,11 @@ void ParticleProcessMaterial::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "collision_bounce", PROPERTY_HINT_RANGE, "0,1,0.01"), "set_collision_bounce", "get_collision_bounce");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "collision_use_scale"), "set_collision_use_scale", "is_collision_using_scale");
 	ADD_GROUP("Sub Emitter", "sub_emitter_");
-	ADD_PROPERTY(PropertyInfo(Variant::INT, "sub_emitter_mode", PROPERTY_HINT_ENUM, "Disabled,Constant,At End,At Collision"), "set_sub_emitter_mode", "get_sub_emitter_mode");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "sub_emitter_mode", PROPERTY_HINT_ENUM, "Disabled:0,Constant:1,At Start:4,At End:2,At Collision:3"), "set_sub_emitter_mode", "get_sub_emitter_mode");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "sub_emitter_frequency", PROPERTY_HINT_RANGE, "0.01,100,0.01,suffix:Hz"), "set_sub_emitter_frequency", "get_sub_emitter_frequency");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "sub_emitter_amount_at_end", PROPERTY_HINT_RANGE, "1,32,1"), "set_sub_emitter_amount_at_end", "get_sub_emitter_amount_at_end");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "sub_emitter_amount_at_collision", PROPERTY_HINT_RANGE, "1,32,1"), "set_sub_emitter_amount_at_collision", "get_sub_emitter_amount_at_collision");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "sub_emitter_amount_at_start", PROPERTY_HINT_RANGE, "1,32,1"), "set_sub_emitter_amount_at_start", "get_sub_emitter_amount_at_start");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "sub_emitter_keep_velocity"), "set_sub_emitter_keep_velocity", "get_sub_emitter_keep_velocity");
 
 	BIND_ENUM_CONSTANT(PARAM_INITIAL_LINEAR_VELOCITY);
@@ -2249,6 +2279,7 @@ void ParticleProcessMaterial::_bind_methods() {
 	BIND_ENUM_CONSTANT(SUB_EMITTER_CONSTANT);
 	BIND_ENUM_CONSTANT(SUB_EMITTER_AT_END);
 	BIND_ENUM_CONSTANT(SUB_EMITTER_AT_COLLISION);
+	BIND_ENUM_CONSTANT(SUB_EMITTER_AT_START);
 	BIND_ENUM_CONSTANT(SUB_EMITTER_MAX);
 
 	BIND_ENUM_CONSTANT(COLLISION_DISABLED);
@@ -2320,6 +2351,7 @@ ParticleProcessMaterial::ParticleProcessMaterial() :
 	set_sub_emitter_frequency(4);
 	set_sub_emitter_amount_at_end(1);
 	set_sub_emitter_amount_at_collision(1);
+	set_sub_emitter_amount_at_start(1);
 	set_sub_emitter_keep_velocity(false);
 
 	set_attractor_interaction_enabled(true);

scene/resources/particle_process_material.h

@@ -96,6 +96,7 @@ public:
 		SUB_EMITTER_CONSTANT,
 		SUB_EMITTER_AT_END,
 		SUB_EMITTER_AT_COLLISION,
+		SUB_EMITTER_AT_START,
 		SUB_EMITTER_MAX
 	};
 
@@ -117,7 +118,7 @@ private:
 		uint64_t emission_shape : 3;
 		uint64_t invalid_key : 1;
 		uint64_t has_emission_color : 1;
-		uint64_t sub_emitter : 2;
+		uint64_t sub_emitter : 3;
 		uint64_t attractor_enabled : 1;
 		uint64_t collision_mode : 2;
 		uint64_t collision_scale : 1;
@@ -282,6 +283,7 @@ private:
 		StringName sub_emitter_frequency;
 		StringName sub_emitter_amount_at_end;
 		StringName sub_emitter_amount_at_collision;
+		StringName sub_emitter_amount_at_start;
 		StringName sub_emitter_keep_velocity;
 
 		StringName collision_friction;
@@ -349,6 +351,7 @@ private:
 	double sub_emitter_frequency = 0.0;
 	int sub_emitter_amount_at_end = 0;
 	int sub_emitter_amount_at_collision = 0;
+	int sub_emitter_amount_at_start = 0;
 	bool sub_emitter_keep_velocity = false;
 	//do not save emission points here
 
@@ -487,6 +490,9 @@ public:
 	void set_sub_emitter_amount_at_collision(int p_amount);
 	int get_sub_emitter_amount_at_collision() const;
 
+	void set_sub_emitter_amount_at_start(int p_amount);
+	int get_sub_emitter_amount_at_start() const;
+
 	void set_sub_emitter_keep_velocity(bool p_enable);
 	bool get_sub_emitter_keep_velocity() const;