1 files changed, 247 insertions, 0 deletions
diff --git a/libdimension/tests/physics.c b/libdimension/tests/physics.c
new file mode 100644
index 0000000..14eeb07
--- /dev/null
+++ b/libdimension/tests/physics.c
@@ -0,0 +1,247 @@
+#include "dimension.h"
+#include <math.h>
+
+typedef struct sphere {
+  dmnsn_vector center;
+  dmnsn_vector velocity;
+  double radius;
+  dmnsn_color color;
+} sphere;
+
+sphere
+make_sphere(size_t x, size_t y, size_t z, size_t size)
+{
+  --size;
+
+  double dx = sin(2*M_PI*x/size);
+  double dy = sin(2*M_PI*y/size);
+  double dz = sin(2*M_PI*z/size);
+  dmnsn_vector c = dmnsn_vector_sub(
+    dmnsn_vector_add(
+      dmnsn_vector_mul(
+        5.0/size,
+        dmnsn_new_vector(x, y, z)
+      ),
+      dmnsn_vector_div(
+        dmnsn_new_vector(dy + dz, dx + dz, dx + dy),
+        4.0
+      )
+    ),
+    dmnsn_new_vector(2.5, 2.5, 2.5)
+  );
+
+  double r = 2.0/size;
+
+  dmnsn_color color = dmnsn_color_from_sRGB(
+    dmnsn_new_color((double)x/size, (double)y/size, (double)z/size)
+  );
+
+  sphere s = {
+    .center = c,
+    .velocity = dmnsn_zero,
+    .radius = r,
+    .color = color,
+  };
+  return s;
+}
+
+dmnsn_array *
+make_spheres()
+{
+  const size_t size = 10;
+  dmnsn_array *spheres = dmnsn_new_array(sizeof(sphere));
+  for (size_t x = 0; x < size; ++x) {
+    for (size_t y = 0; y < size; ++y) {
+      for (size_t z = 0; z < size; ++z) {
+        sphere s = make_sphere(x, y, z, size);
+        dmnsn_array_push(spheres, &s);
+      }
+    }
+  }
+
+  return spheres;
+}
+
+dmnsn_scene *
+make_scene(dmnsn_array *spheres, dmnsn_canvas *canvas, dmnsn_camera *camera)
+{
+  dmnsn_scene *scene = dmnsn_new_scene();
+  DMNSN_INCREF(canvas);
+  scene->canvas = canvas;
+  DMNSN_INCREF(camera);
+  scene->camera = camera;
+
+  scene->default_texture->pigment = dmnsn_new_solid_pigment(dmnsn_black);
+  scene->default_texture->finish.ambient = dmnsn_new_basic_ambient(
+    dmnsn_color_from_sRGB(dmnsn_color_mul(0.25, dmnsn_white))
+  );
+  scene->default_texture->finish.diffuse = dmnsn_new_lambertian(
+    dmnsn_sRGB_inverse_gamma(0.8)
+  );
+
+  scene->background = dmnsn_new_solid_pigment(
+    dmnsn_color_from_sRGB(
+      dmnsn_color_mul(0.5, dmnsn_new_color(0.73, 0.90, 0.97))
+    )
+  );
+
+  DMNSN_ARRAY_FOREACH (sphere *, s, spheres) {
+    dmnsn_object *sph = dmnsn_new_sphere();
+
+    sph->texture = dmnsn_new_texture();
+    sph->texture->pigment = dmnsn_new_solid_pigment(s->color);
+    double maxcomponent = dmnsn_max(
+      dmnsn_max(s->color.R, s->color.G),
+      s->color.B
+    );
+    dmnsn_color reflcolor;
+    if (maxcomponent >= dmnsn_epsilon) {
+      reflcolor = dmnsn_color_mul(0.5/maxcomponent, s->color);
+    } else {
+      reflcolor = dmnsn_color_mul(0.25, dmnsn_white);
+    }
+    sph->texture->finish.reflection = dmnsn_new_basic_reflection(
+      dmnsn_black, reflcolor, 1.0
+    );
+
+    sph->trans = dmnsn_matrix_mul(
+      dmnsn_translation_matrix(s->center),
+      dmnsn_scale_matrix(dmnsn_new_vector(s->radius, s->radius, s->radius))
+    );
+
+    dmnsn_array_push(scene->objects, &sph);
+  }
+
+  dmnsn_object *plane = dmnsn_new_plane(dmnsn_y);
+  plane->trans = dmnsn_translation_matrix(dmnsn_vector_mul(-4.0, dmnsn_y));
+  plane->texture = dmnsn_new_texture();
+  plane->texture->pigment = dmnsn_new_solid_pigment(
+    dmnsn_color_from_sRGB(dmnsn_new_color(0.73, 0.90, 0.97))
+  );
+  plane->texture->finish.ambient = dmnsn_new_basic_ambient(
+    dmnsn_color_from_sRGB(dmnsn_color_mul(0.5, dmnsn_white))
+  );
+  plane->texture->finish.diffuse = dmnsn_new_lambertian(
+    dmnsn_sRGB_inverse_gamma(0.7)
+  );
+  dmnsn_array_push(scene->objects, &plane);
+
+  dmnsn_color lcolor = dmnsn_color_mul(1.0/4.0, dmnsn_white);
+  dmnsn_light *light;
+  light = dmnsn_new_point_light(dmnsn_new_vector(-3.0, 0.0, -5.0), lcolor);
+  dmnsn_array_push(scene->lights, &light);
+  light = dmnsn_new_point_light(dmnsn_new_vector(-1.0, 0.0, -5.0), lcolor);
+  dmnsn_array_push(scene->lights, &light);
+  light = dmnsn_new_point_light(dmnsn_new_vector(+1.0, 0.0, -5.0), lcolor);
+  dmnsn_array_push(scene->lights, &light);
+  light = dmnsn_new_point_light(dmnsn_new_vector(+3.0, 0.0, -5.0), lcolor);
+  dmnsn_array_push(scene->lights, &light);
+  light = dmnsn_new_point_light(dmnsn_new_vector(-3.0, 5.0, -5.0), lcolor);
+  dmnsn_array_push(scene->lights, &light);
+  light = dmnsn_new_point_light(dmnsn_new_vector(-1.0, 5.0, -5.0), lcolor);
+  dmnsn_array_push(scene->lights, &light);
+  light = dmnsn_new_point_light(dmnsn_new_vector(+1.0, 5.0, -5.0), lcolor);
+  dmnsn_array_push(scene->lights, &light);
+  light = dmnsn_new_point_light(dmnsn_new_vector(+3.0, 5.0, -5.0), lcolor);
+  dmnsn_array_push(scene->lights, &light);
+
+  scene->nthreads = 12; /* XXX */
+  return scene;
+}
+
+void
+integrate_spheres(dmnsn_array *spheres, double h)
+{
+  static const double g = 5.0;
+
+  /* Inter-object collision detection */
+  DMNSN_ARRAY_FOREACH (sphere *, s1, spheres) {
+    DMNSN_ARRAY_FOREACH (sphere *, s2, spheres) {
+      if (s1 == s2) continue;
+
+      dmnsn_vector deltar = dmnsn_vector_sub(s1->center, s2->center);
+      dmnsn_vector deltav = dmnsn_vector_sub(s1->velocity, s2->velocity);
+      if (dmnsn_vector_norm(deltar) <= s1->radius + s2->radius
+          && dmnsn_vector_dot(deltar, deltav) < 0.0)
+      {
+        dmnsn_vector x = dmnsn_vector_normalized(deltar);
+        dmnsn_vector v1 = s1->velocity;
+        double x1 = dmnsn_vector_dot(x, v1);
+        dmnsn_vector v1x = dmnsn_vector_mul(x1, x);
+        dmnsn_vector v1y = dmnsn_vector_sub(v1, v1x);
+
+        x = dmnsn_vector_negate(x);
+        dmnsn_vector v2 = s2->velocity;
+        double x2 = dmnsn_vector_dot(x, v2);
+        dmnsn_vector v2x = dmnsn_vector_mul(x2, x);
+        dmnsn_vector v2y = dmnsn_vector_sub(v2, v2x);
+
+        s1->velocity = dmnsn_vector_add(v2x, v1y);
+        s2->velocity = dmnsn_vector_add(v1x, v2y);
+      }
+    }
+  }
+
+  /* Floor collision detection */
+  DMNSN_ARRAY_FOREACH (sphere *, s, spheres) {
+    if (s->center.y - s->radius <= -4.0) {
+      s->velocity.y = fabs(s->velocity.y);
+    }
+  }
+
+  /* Advance by the timestep */
+  DMNSN_ARRAY_FOREACH (sphere *, s, spheres) {
+    s->center = dmnsn_vector_add(s->center, dmnsn_vector_mul(h, s->velocity));
+    s->center.y -= g*h*h/2.0;
+    s->velocity.y -= g*h;
+  }
+}
+
+int
+main()
+{
+  dmnsn_die_on_warnings(true);
+
+  const double h = 1.0/25.0;
+  const int nframes = 401;
+  const size_t width = 1920, height = 1080;
+
+  dmnsn_array *spheres = make_spheres();
+
+  dmnsn_canvas *canvas = dmnsn_new_canvas(width, height);
+  dmnsn_png_optimize_canvas(canvas);
+
+  dmnsn_camera *camera = dmnsn_new_perspective_camera();
+  camera->trans = dmnsn_new_matrix(
+    1.7151356822004125, -0.12253122769681897, -0.2328451577118997, 3.0,
+    0.0, 0.8849477555881373, -0.4656903154237999, 6.0,
+    0.46776427696374845, 0.4492811682216699, 0.8537655782769662, -11.0
+  );
+
+  for (int i = 0; i < nframes; ++i) {
+    if (i > 0) {
+      printf("Frame %d:\t Integrating\n", i);
+      static const int precision = 100;
+      for (int j = 0; j < precision; ++j)
+        integrate_spheres(spheres, h/precision);
+    }
+
+    printf("Frame %d:\t Rendering\n", i);
+    dmnsn_scene *scene = make_scene(spheres, canvas, camera);
+    dmnsn_ray_trace(scene);
+
+    printf("Frame %d:\t Exporting\n", i);
+    char fname[] = "physics00000.png";
+    sprintf(fname, "physics%05d.png", i);
+    FILE *image = fopen(fname, "wb");
+    dmnsn_png_write_canvas(canvas, image);
+    fclose(image);
+
+    dmnsn_delete_scene(scene);
+  }
+
+  dmnsn_delete_camera(camera);
+  dmnsn_delete_canvas(canvas);
+  dmnsn_delete_array(spheres);
+  return 0;
+}