starfield/main.c

#include "aliases.h"
#include <SDL2/SDL.h>
#include <SDL2/SDL_pixels.h>
#include <SDL2/SDL_rect.h>
#include <SDL2/SDL_render.h>
#include <SDL2/SDL_surface.h>
#include <SDL2/SDL_timer.h>
#include <SDL2/SDL_video.h>
#include <math.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define WINDOW_WIDTH 800
#define WINDOW_HEIGHT 600

#define NORMALISED_MIN -1
#define NORMALISED_MAX 1

#define STAR_COUNT 2500
#define STAR_SPREAD 500
#define STAR_SPEED 50

#define BG_COLOR 0x060616ff
#define STAR_COLOR 0xd4d4ddff

#define PROJECTION_PLANE 1.0

typedef struct {
  u32 x;
  u32 y;
} vec2i_t;

typedef struct {
  f64 x;
  f64 y;
} vec2f_t;

typedef struct {
  f64 x;
  f64 y;
  f64 z;
} vec3f_t;

f64 absf(f64 val);
void render_clear(SDL_Surface *surface, u32 color);
void set_pixel(SDL_Surface *surface, vec2i_t pos, u32 color);

#if 0
void fill_rect(SDL_Surface *surface, vec2i_t pos, u32 w, u32 h, u32 color);
f64 normalise(f64 abs_val, f64 abs_min, f64 abs_max, f64 norm_min,
              f64 norm_max);
#endif

f64 denormalise(f64 norm_val, f64 norm_min, f64 norm_max, f64 abs_min,
                f64 abs_max);
void init_starfield(vec3f_t *stars, u32 count, i32 spread);
void update_startfield(vec3f_t *stars, u32 count, i32 spread, u32 speed,
                       f64 delta);
void render_starfield(SDL_Surface *surface, vec3f_t *stars, u32 count,
                      i32 spread);

int main(void) {
  srand(time(NULL));

  SDL_Init(SDL_INIT_EVERYTHING);

  SDL_Window *window = SDL_CreateWindow("Starfield", SDL_WINDOWPOS_CENTERED,
                                        SDL_WINDOWPOS_CENTERED, WINDOW_WIDTH,
                                        WINDOW_HEIGHT, SDL_WINDOW_SHOWN);

  SDL_Surface *surface = SDL_GetWindowSurface(window);

  SDL_Surface *canvas = SDL_CreateRGBSurfaceWithFormat(
      0, surface->w, surface->h, 32, SDL_PIXELFORMAT_ABGR32);

  bool running = true;

  SDL_Event event = {0};

  vec3f_t stars[STAR_COUNT];

  init_starfield(stars, STAR_COUNT, STAR_SPREAD);

  f64 delta = 1.0 / 60.0; // constant delta

  while (running) {
    while (SDL_PollEvent(&event)) {
      switch (event.type) {
      case SDL_QUIT:
        running = false;
        break;
      }
    }

    update_startfield(stars, STAR_COUNT, STAR_SPREAD, STAR_SPEED, delta);

    render_clear(canvas, BG_COLOR);

    render_starfield(canvas, stars, STAR_COUNT, STAR_SPREAD);

    SDL_BlitSurface(canvas, NULL, surface, NULL);

    SDL_UpdateWindowSurface(window);
  }

  SDL_DestroyWindow(window);

  SDL_Quit();

  return EXIT_SUCCESS;
}

f64 absf(f64 val) {
  if (val < 0) {
    val *= -1.0;
  }

  return val;
}

void render_clear(SDL_Surface *surface, u32 color) {
  u32 length = surface->w * surface->h;

  SDL_LockSurface(surface);

  u32 *pixels = (u32 *)(surface->pixels);

  for (u32 i = 0; i < length; ++i) {
    pixels[i] = color;
  }

  SDL_UnlockSurface(surface);
}

void set_pixel(SDL_Surface *surface, vec2i_t pos, u32 color) {
  SDL_LockSurface(surface);

  u32 *pixels = (u32 *)(surface->pixels);

  u32 index = pos.y * surface->w + pos.x;

  if (index < surface->w * surface->h) {
    pixels[index] = color;
  }

  SDL_UnlockSurface(surface);
}

#if 0
void fill_rect(SDL_Surface *surface, vec2i_t pos, u32 w, u32 h, u32 color) {
  SDL_LockSurface(surface);

  u32 *pixels = (u32 *)(surface->pixels);

  for (u32 row = 0; row < h; ++row) {
    for (u32 col = 0; col < w; ++col) {
      u32 i = (pos.y + row) * surface->w + (pos.x + col);

      pixels[i] = color;
    }
  }

  SDL_UnlockSurface(surface);
}

f64 normalise(f64 abs_val, f64 abs_min, f64 abs_max, f64 norm_min,
              f64 norm_max) {
  if (abs_min - abs_max == 0.0) {
    return NAN;
  }

  f64 ratio = (abs_val - abs_max) / (abs_min - abs_max);

  return ratio * (norm_min - norm_max) + norm_max;
}
#endif

f64 denormalise(f64 norm_val, f64 norm_min, f64 norm_max, f64 abs_min,
                f64 abs_max) {
  if (norm_min - norm_max == 0.0) {
    return NAN;
  }

  f64 ratio = (norm_val - norm_max) / (norm_min - norm_max);

  return ratio * (abs_min - abs_max) + abs_max;
}

vec3f_t init_star_position(i32 spread) {
  i32 spread_half = spread / 2;

  return (vec3f_t){.x = ((rand() % spread) - spread_half) * 2.0,
                   .y = ((rand() % spread) - spread_half) * 2.0,
                   .z = (rand() % spread) + PROJECTION_PLANE};
}

void init_starfield(vec3f_t *stars, u32 count, i32 spread) {
  for (u32 i = 0; i < count; ++i) {
    stars[i] = init_star_position(spread);
  }
}

void update_startfield(vec3f_t *stars, u32 count, i32 spread, u32 speed,
                       f64 delta) {
  for (u32 i = 0; i < count; ++i) {
    stars[i].z -= speed * delta;

    if (stars[i].z < PROJECTION_PLANE) {
      stars[i] = init_star_position(spread);
    }
  }
}

void render_starfield(SDL_Surface *surface, vec3f_t *stars, u32 count,
                      i32 spread) {
  vec2f_t projected[count];
  vec2i_t coords;

  for (u32 i = 0; i < count; ++i) {
    if (stars[i].z == 0.0) {
      continue;
    }

    projected[i] =
        (vec2f_t){.x = stars[i].x / stars[i].z, .y = stars[i].y / stars[i].z};

    if (projected[i].x < NORMALISED_MIN || projected[i].x > NORMALISED_MAX ||
        projected[i].y < NORMALISED_MIN || projected[i].y > NORMALISED_MAX ||
        (projected[i].x == 0.0 && projected[i].y == 0.0)) {
      stars[i] = init_star_position(spread);

      continue;
    }

    projected[i].x = denormalise(projected[i].x, NORMALISED_MIN, NORMALISED_MAX,
                                 0, WINDOW_WIDTH);
    projected[i].y = denormalise(projected[i].y, NORMALISED_MIN, NORMALISED_MAX,
                                 0, WINDOW_HEIGHT);

    coords =
        (vec2i_t){.x = (u32)ceil(projected[i].x), .y = (u32)projected[i].y};

    set_pixel(surface, coords, STAR_COLOR);
  }
}