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#include "particle.h"
#include "types.h"
#include "shader.h"
#include <stdlib.h>
#include <float.h>
void respawn_particle(struct particle *particle, struct object object, v2 offset)
{
f32 random = ((rand() % 100) - 50) / 10.0f;
particle->pos = addf_v2(add_v2(object.pos, offset), random);
particle->vel = scale_v2(object.vel, 0.1f);
random = 0.5f + ((rand() % 100) / 100.0f);
particle->color = (v4){random, random, random, 1.0f};
particle->life = 1.0f;
}
i32 find_unused_particle(struct particle_generator generator)
{
f32 min = FLT_MAX;
i32 mini = 0;
for (i32 i = 0; i < MAX_PARTICLES; i++) {
f32 life = generator.particles[i].life;
if (life <= 0.0f) {
return i;
} else if (life < min) {
min = life;
mini = i;
}
}
return mini;
}
struct particle_generator init_generator(i32 new, u32 shader, u32 texture)
{
struct particle_generator generator = {0};
reset_particles(&generator);
generator.new = new;
generator.shader = shader;
generator.texture = texture;
f32 vertices[] = {
0.0f, 0.0f, 0.0f, 0.0f,
1.0f, 0.0f, 1.0f, 0.0f,
0.0f, 1.0f, 0.0f, 1.0f,
1.0f, 0.0f, 1.0f, 0.0f,
1.0f, 1.0f, 1.0f, 1.0f,
0.0f, 1.0f, 0.0f, 1.0f
};
u32 vao, vbo;
glGenVertexArrays(1, &vao);
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindVertexArray(vao);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 4, GL_FLOAT, 0, 4 * sizeof(f32), 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
generator.vao = vao;
return generator;
}
void update_particles(struct particle_generator *generator, struct object object, f32 dt, v2 offset)
{
for (i32 i = 0; i < generator->new; i++) {
i32 unused = find_unused_particle(*generator);
respawn_particle(generator->particles + unused, object, offset);
}
for (i32 i = 0; i < MAX_PARTICLES; i++) {
struct particle *particle = generator->particles + i;
particle->life -= dt;
if (particle->life > 0.0f) {
particle->pos = sub_v2(particle->pos, scale_v2(particle->vel, dt));
particle->color.w -= dt * 2.0f;
}
}
}
void render_particles(struct particle_generator generator)
{
glBlendFunc(GL_SRC_ALPHA, GL_ONE);
glUseProgram(generator.shader);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, generator.texture);
glBindVertexArray(generator.vao);
for (i32 i = 0; i < MAX_PARTICLES; i++) {
struct particle *particle = generator.particles + i;
if (particle->life > 0.0f) {
uniform_v2(generator.shader, "offset", particle->pos);
uniform_v4(generator.shader, "color", particle->color);
glDrawArrays(GL_TRIANGLES, 0, 6);
}
}
glBindVertexArray(0);
glUseProgram(0);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}
void reset_particles(struct particle_generator *generator)
{
for (i32 i = 0; i < MAX_PARTICLES; i++)
generator->particles[i] = (struct particle)default_particle;
}
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