demo/src/particles.h

#pragma once

#include "defines.h"
#include "colour.h"
#include <glm/glm.hpp>
#include <vector>

BEGIN_NAMESPACE

struct particle;
struct particle_emitter;
struct particle_modifier;

using particle_list = std::vector<particle *>;
using particle_emitter_list = std::vector<particle_emitter *>;
using particle_modifier_list = std::vector<particle_modifier *>;

struct particle {
    glm::vec3 position;
    glm::vec3 old_pos;
    glm::vec3 velocity;
    colour color;
    float life;
    float size;
};

struct particle_emitter {
    particle_emitter();
    virtual ~particle_emitter() = default;

    particle *new_particle();
    void update(float elapsed_ms);

    virtual void spawn(particle *p) = 0;

    particle_list particles;
    particle_list dead_particles;

    glm::vec3 position{};
    float emission_rate{}; // particles per second
    float to_spawn;
    float life_decay{};
    colour start_colour{};
    colour end_colour{};
    float start_size;
    float end_size;
};

struct particle_modifier {
    virtual void affect_particle(particle *p, float elapsed_ms) = 0;
};

struct particle_system {
    void update(float elapsed_ms);
    void render();

    particle_list particles;
    particle_emitter_list emitters;
    particle_modifier_list modifiers;
};

struct dot_particle_emitter : particle_emitter {
    dot_particle_emitter();
    void spawn(particle *p) override;
};


struct particle_attractor : particle_modifier {
    void init(glm::vec3& center, float strength_);
    void affect_particle(particle *p, float elapsed_ms) override;

    glm::vec3 attractor_center;
    float strength;
};

END_NAMESPACE