Zoom + frame of reference

PlanetarySystem.c

@@ -36,6 +36,8 @@ PlanetarySystem *planetary_system_create(double interval) {
     planetary_system->objects_length = 6;
     planetary_system->objects = (CelestialObject **)malloc(sizeof(PlanetarySystem *) * planetary_system->objects_length);
     planetary_system->interval = interval;
+    planetary_system->zoom_factor = 1;
+    planetary_system->reference_frame_object_index = 0;
 
     planetary_system->objects[0] = celestial_object_create(SUN_MASS, 0, 0, 50, 0x00FFFFFF);
     planetary_system->objects[1] = celestial_object_create(MERCURY_MASS, MERCURY_SEMI_MAJOR_AXIS, MERCURY_ECCENTRICITY, 10, 0x00DBCECA);
@@ -88,13 +90,11 @@ void planetary_system_update(PlanetarySystem *planetary_system) {
 
             Vector2 r = vector2_normalize(vector2_create(current_position.y, -current_position.x));
             Vector2 periapsis_velocity = vector2_multiply(r, periapsis_velocity_scalar);
-            vector2_print(periapsis_velocity);
 
             new_position = vector2_add(current_position, vector2_multiply(periapsis_velocity, planetary_system->interval));
             Vector2 a = calculate_gravitational_acceleration(planetary_system, i);
             new_position = vector2_add(new_position, vector2_multiply(a, 0.5 * pow(planetary_system->interval, 2)));
         } else {
-            // continue;
             new_position = vector2_substract(vector2_multiply(current_position, 2), object->previous_position);
             Vector2 a = calculate_gravitational_acceleration(planetary_system, i);
             new_position = vector2_add(new_position, vector2_multiply(a, pow(planetary_system->interval, 2)));
@@ -116,9 +116,9 @@ void planetary_system_draw(PlanetarySystem *planetary_system, struct gfx_context
 
     for (uint32_t i = 0; i < planetary_system->objects_length; i += 1) {
         CelestialObject *object = planetary_system->objects[i];
-        // Vector2 tmp = vector2_substract(object->current_position, planetary_system->objects[3]->current_position);
-        // tmp = vector2_multiply(tmp, 1);
-        Vector2 scaled_position = scale_position(object->current_position);
+        Vector2 tmp = vector2_substract(object->current_position, planetary_system->objects[planetary_system->reference_frame_object_index]->current_position);
+        tmp = vector2_multiply(tmp, planetary_system->zoom_factor);
+        Vector2 scaled_position = scale_position(tmp);
 
         draw_full_circle(context, scaled_position.x, scaled_position.y, object->drawing_disc_radius, object->drawing_color);
     }

PlanetarySystem.h

@@ -13,6 +13,8 @@ typedef struct {
     uint32_t objects_length;
     CelestialObject **objects;
     double interval;
+    double zoom_factor;
+    uint32_t reference_frame_object_index;
 } PlanetarySystem;
 
 PlanetarySystem *planetary_system_create(double interval);

main.c

@@ -18,8 +18,8 @@ int main() {
         return EXIT_FAILURE;
     }
 
-    int32_t time_elapsing_per_second = 3600 * 24 * 10;
-    int32_t refresh_rate = 480;
+    int32_t time_elapsing_per_second = 3600 * 24 * 5;
+    int32_t refresh_rate = 240;
     int32_t elapsed_time = 0;
     double sleep_duration = 1.0 / refresh_rate * 1E9;
     printf("%lf\n", (double)time_elapsing_per_second / refresh_rate);
@@ -39,8 +39,42 @@ int main() {
             SDL_SetWindowTitle(context->window, title);
         }
 
-        if (gfx_keypressed() == SDLK_ESCAPE)
-            break;
+        SDL_Event event;
+        if (SDL_PollEvent(&event)) {
+            if (event.type == SDL_MOUSEWHEEL) {
+                if (event.wheel.y > 0) {
+                    planetary_system->zoom_factor *= 1.1;
+                } else if (event.wheel.y < 0) {
+                    planetary_system->zoom_factor /= 1.1;
+
+                    if (planetary_system->zoom_factor < 1) {
+                        planetary_system->zoom_factor = 1;
+                    }
+                }
+            }
+
+            if (event.type == SDL_KEYDOWN) {
+                if (event.key.keysym.sym == SDLK_ESCAPE) {
+                    break;
+                }
+
+                if (event.key.keysym.sym == SDLK_LEFT) {
+                    planetary_system->reference_frame_object_index -= 1;
+                    planetary_system->reference_frame_object_index %= planetary_system->objects_length;
+                }
+
+                if (event.key.keysym.sym == SDLK_RIGHT) {
+                    planetary_system->reference_frame_object_index += 1;
+                    planetary_system->reference_frame_object_index %= planetary_system->objects_length;
+                }
+            }
+        }
+
+        // if (gfx_keypressed() == SDLK_ESCAPE)
+        //     break;
+        // if (gfx_keypressed() == SDL_MOUSEBUTTONDOWN) {
+        //     printf("A");
+        // }
         struct timespec t = {.tv_sec = 0, .tv_nsec = sleep_duration};
         nanosleep(&t, NULL);
         elapsed_time += 1;