Add particle curve input for number of existing particles (#6889)

* Add code to process global starts for modular curves

* Add particle curve input for number of existing particles

Author: BMagnu

code/particle/ParticleEffect.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include "globalincs/pstypes.h"
+#include "globalincs/systemvars.h"
 #include "particle/ParticleVolume.h"
 #include "particle/ParticleSource.h"
 #include "utils/RandomRange.h"
@@ -228,6 +229,11 @@ class ParticleEffect {
 		std::pair {"Effects Running", modular_curves_math_input<
 		    modular_curves_submember_input<&ParticleSource::m_effect_is_running, &decltype(ParticleSource::m_effect_is_running)::count>,
 			modular_curves_submember_input<&ParticleSource::getEffect, &SCP_vector<ParticleEffect>::size>,
+			ModularCurvesMathOperators::division>{}},
+		std::pair {"Total Particle Count", modular_curves_global_submember_input<get_particle_count>{}},
+		std::pair {"Particle Usage Score", modular_curves_math_input<
+		    modular_curves_global_submember_input<get_particle_count>,
+			modular_curves_global_submember_input<Detail, &detail_levels::num_particles>,
 			ModularCurvesMathOperators::division>{}})
 	.derive_modular_curves_input_only_subset<size_t>( //Effect Number
 		std::pair {"Spawntime Left", modular_curves_functional_full_input<&ParticleSource::getEffectRemainingTime>{}},

code/particle/particle.cpp

@@ -113,6 +113,10 @@ namespace particle
 		Particles.clear();
 	}
 
+	size_t get_particle_count() {
+		return Particles.size() + Persistent_particles.size();
+	}
+
 	void page_in()
 	{
 		if (!Particles_enabled)

code/particle/particle.h

@@ -40,6 +40,8 @@ namespace particle
 	// kill all active particles
 	void kill_all();
 
+	size_t get_particle_count();
+
 
 	//============================================================================
 	//=============== LOW-LEVEL SINGLE PARTICLE CREATION CODE ====================

code/utils/modular_curves.h

@@ -178,6 +178,44 @@ struct modular_curves_submember_input_full : public modular_curves_submember_inp
 	}
 };
 
+template<const auto& global, auto... grabbers>
+struct modular_curves_global_submember_input {
+protected:
+	template<typename result_type>
+	static inline float number_to_float(const result_type& number) {
+		// if constexpr(std::is_same_v<std::decay_t<result_type>, fix>) // TODO: Make sure we can differentiate fixes from ints.
+		// 	return f2fl(number);
+		// else
+		if constexpr(std::is_integral_v<std::decay_t<result_type>>)
+			return static_cast<float>(number);
+		else if constexpr(std::is_floating_point_v<std::decay_t<result_type>>)
+			return static_cast<float>(number);
+		else {
+			static_assert(!std::is_same_v<result_type, result_type>, "Tried to return non-numeric value");
+			return 0.f;
+		}
+	}
+
+public:
+	template<int /*tuple_idx*/, typename input_type>
+	static inline float grab(const input_type& /*input*/) {
+		if constexpr (sizeof...(grabbers) == 0) {
+			if constexpr (std::is_invocable_v<std::decay_t<decltype(global)>>) {
+				return number_to_float(global());
+			} else {
+				return number_to_float(global);
+			}
+		}
+		else {
+			if constexpr (std::is_invocable_v<std::decay_t<decltype(global)>>) {
+				return modular_curves_submember_input<grabbers...>::template grab<-1, decltype(global())>(global());
+			} else {
+				return modular_curves_submember_input<grabbers...>::template grab<-1, std::decay_t<decltype(global)>>(global);
+			}
+		}
+	}
+};
+
 template<auto grabber_fnc>
 struct modular_curves_functional_input {
   private:
@@ -227,7 +265,7 @@ enum class ModularCurvesMathOperators {
 	addition,
 	subtraction,
 	multiplication,
-	division,
+	division
 };
 
 template <typename first, typename second, auto operation>