njin_particles.h

#pragma once
#include "_math.h"
#include "_types.h"
#include "njin_draw.h"
#include <entt/entity/fwd.hpp>
#include <vector>
 
namespace njin {
struct context;


struct f32_range {
  f32 min = 0.0f; 
  f32 max = 0.0f; 
};

enum particle_shape {
  particle_circle, 
  particle_square, 
};

struct particle {
  vec2 pos{};        
  vec2 velocity{};   
  f32 age = 0.0f;    
  f32 life = 1.0f;   
  f32 rot = 0.0f;    
  f32 spin = 0.0f;   
  f32 size = 1.0f;   
};

struct particle_emitter {
  f32 rate = 0.0f;       
  bool emitting = true;  
  i32 max_particles = 512; 
  vec2 area{};

  f32_range life{0.5f, 1.0f};     
  f32_range speed{50.0f, 100.0f}; 
  f32 angle = 0.0f;
  f32 spread = 360.0f;
  vec2 gravity{};     
  f32 drag = 0.0f;    
  f32_range spin{};   
  bool local_space = false;

  f32 size_start = 8.0f; 
  f32 size_end = 0.0f;   
  f32_range size_jitter{1.0f, 1.0f}; 
  rgba color_start{1.0f, 1.0f, 1.0f, 1.0f}; 
  rgba color_end{1.0f, 1.0f, 1.0f, 0.0f};   
  particle_shape shape = particle_circle; 
  texture_handle texture{};
  rect source{};  
  blend_mode blend = blend_alpha; 
  i32 layer = 0;  
  bool visible = true; 

  bool destroy_when_done = false;

  std::vector<particle> particles; 
  i32 pending_burst = 0; 
  f32 emit_accum = 0.0f; 
  bool gpu = false;
};

enum particle_backend {
  particle_backend_auto,
  particle_backend_cpu, 
};

void particles_set_backend(context &ctx, particle_backend backend);

particle_backend particles_backend(const context &ctx);

bool particles_gpu_available(context &ctx);

inline void particles_burst(particle_emitter &emitter, i32 count) {
  if (count > 0)
    emitter.pending_burst += count;
}

entt::entity particles_spawn(context &ctx, const particle_emitter &preset,
                             vec2 pos, i32 count);
} // namespace njin