Add tail line

CelestialObject.c

@@ -18,6 +18,8 @@ CelestialObject *celestial_object_create(double mass, double semi_major_axis, do
     object->eccentricity = eccentricity;
     object->drawing_disc_radius = drawing_disc_radius;
     object->drawing_color = drawing_color;
+    object->points = (Vector2 *)malloc(sizeof(Vector2) * 200);
+    object->points_length = 0;
 
     return object;
 }

CelestialObject.h

@@ -3,7 +3,6 @@
 
 #include "Vector2.h"
 
-typedef struct CelestialObject CelestialObject;
 typedef struct CelestialObject {
     double mass;
     Vector2 previous_position;
@@ -12,6 +11,8 @@ typedef struct CelestialObject {
     double eccentricity;
     uint32_t drawing_disc_radius;
     uint32_t drawing_color;
+    Vector2 *points;
+    int32_t points_length;
 } CelestialObject;
 
 CelestialObject *celestial_object_create(double mass, double semi_major_axis, double eccentricity, uint32_t drawing_disc_radius, uint32_t drawing_color);

PlanetarySystem.c

@@ -68,7 +68,7 @@ Vector2 calculate_gravitational_acceleration(PlanetarySystem *planetary_system,
     return a;
 }
 
-void planetary_system_update(PlanetarySystem *planetary_system, double interval) {
+void planetary_system_update(PlanetarySystem *planetary_system, double interval, bool save_position) {
     for (uint32_t i = 1; i < planetary_system->objects_length; i += 1) {
         CelestialObject *object = planetary_system->objects[i];
         Vector2 current_position = object->current_position;
@@ -101,33 +101,62 @@ void planetary_system_update(PlanetarySystem *planetary_system, double interval)
 
         object->previous_position = object->current_position;
         object->current_position = new_position;
+
+        if (object->points_length < 200 && save_position) {
+            object->points[object->points_length] = object->current_position;
+            object->points_length += 1;
+        } else if (save_position) {
+            for (int32_t j = 1; j < object->points_length; j += 1) {
+                object->points[j - 1] = object->points[j];
+            }
+
+            object->points[object->points_length - 1] = object->current_position;
+        }
     }
 }
 
-Vector2 scale_position(Vector2 position) {
-    Vector2 scaled_position = vector2_multiply(position, 1.0 / (260 * 1E9));
+Vector2 scale_position(PlanetarySystem *planetary_system, Vector2 object_position, Vector2 reference_frame_position) {
+    Vector2 unscaled_position = vector2_substract(object_position, reference_frame_position);
+    unscaled_position = vector2_multiply(unscaled_position, planetary_system->zoom_factor);
+
+    Vector2 scaled_position = vector2_multiply(unscaled_position, 1.0 / (300 * 1E9));
     scaled_position = vector2_fit_canvas(scaled_position, SCREEN_WIDTH, SCREEN_HEIGHT);
     return scaled_position;
 }
 
+void draw_disc(Vector2 position, uint32_t radius) {
+    glBegin(GL_POLYGON);
+    for (uint32_t i = 0; i < 360; i += 1) {
+        double theta = i * 3.1415 / 180;
+        double x = position.x + radius * cos(theta);
+        double y = position.y + radius * sin(theta);
+        glVertex2f(x, y);
+    }
+    glEnd();
+}
+
 void planetary_system_draw(PlanetarySystem *planetary_system) {
+    CelestialObject *reference_frame = planetary_system->objects[planetary_system->reference_frame_object_index];
+
     for (uint32_t i = 0; i < planetary_system->objects_length; i += 1) {
         CelestialObject *object = planetary_system->objects[i];
-        Vector2 unscaled_position = vector2_substract(object->current_position, planetary_system->objects[planetary_system->reference_frame_object_index]->current_position);
-        unscaled_position = vector2_multiply(unscaled_position, planetary_system->zoom_factor);
-        Vector2 scaled_position = scale_position(unscaled_position);
+        Vector2 scaled_position = scale_position(planetary_system, object->current_position, reference_frame->current_position);
 
         uint32_t color = object->drawing_color;
         glColor3ub((color & 0xFF0000) >> 16, (color & 0x00FF00) >> 8, (color & 0x0000FF) >> 0);
-        glBegin(GL_POLYGON);
-
-        for (uint32_t i = 0; i < 360; i += 1) {
-            double theta = i * 3.1415 / 180;
-            double x = scaled_position.x + object->drawing_disc_radius * cos(theta);
-            double y = scaled_position.y + object->drawing_disc_radius * sin(theta);
-            glVertex2f(x, y);
+        draw_disc(scaled_position, object->drawing_disc_radius);
+
+        if (i != 5) {
+            glLineWidth(4.0);
+
+            for (int32_t j = 0; j < object->points_length - 1; j += 1) {
+                glBegin(GL_LINES);
+                Vector2 aaa = scale_position(planetary_system, object->points[j], reference_frame->current_position);
+                glVertex2f(aaa.x, aaa.y);
+                Vector2 bbb = scale_position(planetary_system, object->points[j + 1], reference_frame->current_position);
+                glVertex2f(bbb.x, bbb.y);
+                glEnd();
+            }
         }
-
-        glEnd();
     }
 }

PlanetarySystem.h

@@ -17,7 +17,7 @@ typedef struct {
 } PlanetarySystem;
 
 PlanetarySystem *planetary_system_create();
-void planetary_system_update(PlanetarySystem *planetary_system, double interval);
+void planetary_system_update(PlanetarySystem *planetary_system, double interval, bool save_position);
 void planetary_system_draw(PlanetarySystem *planetary_system);
 
 #endif

main.c

@@ -8,9 +8,9 @@
 #include "Vector2.h"
 
 #define WINDOW_NAME "Solar System"
-#define REFRESH_RATE 100
-#define UPDATE_RATE 10000
-#define TIME_ELASPING_PER_SECOND 3600 * 24 * 30
+#define REFRESH_RATE 200
+#define TIME_ELASPING_PER_SECOND 3600 * 24 * 80
+#define TIME_ELASPING_PER_UPDATE 100
 
 // https://stackoverflow.com/questions/3417837/what-is-the-best-way-to-suppress-a-unused-variable-x-warning
 #ifdef UNUSED
@@ -29,12 +29,15 @@ uint32_t true_time_shift = 0;
 void draw_timer() {
     glutPostRedisplay();
     glutTimerFunc(1000 / REFRESH_RATE, draw_timer, 0);
-    elapsed_time += 1;
 }
 
 void update_timer() {
-    for (uint32_t i = 0; i < UPDATE_RATE / REFRESH_RATE; i += 1) {
-        planetary_system_update(planetary_system, (double)TIME_ELASPING_PER_SECOND / UPDATE_RATE);
+    if (elapsed_time == 0)
+        true_time_shift = time(NULL) % 1000;
+    elapsed_time += 1;
+
+    for (uint32_t i = 0; i < TIME_ELASPING_PER_SECOND / REFRESH_RATE / TIME_ELASPING_PER_UPDATE; i += 1) {
+        planetary_system_update(planetary_system, TIME_ELASPING_PER_UPDATE, i == 0);
     }
 
     glutTimerFunc(1000 / REFRESH_RATE, update_timer, 0);
@@ -44,7 +47,7 @@ void draw() {
     glClearColor(0.0, 0.0, 0.0, 1.0);
     glClear(GL_COLOR_BUFFER_BIT);
 
-    if (elapsed_time % REFRESH_RATE == 0) {
+    if (elapsed_time % REFRESH_RATE == 0 && elapsed_time != 0) {
         char title[100];
         sprintf(title, "Solar System (%d : %ld)", elapsed_time / REFRESH_RATE, (time(NULL) - true_time_shift) % 1000);
         glutSetWindowTitle(title);
@@ -84,10 +87,6 @@ void handle_mouse_input(int button, int state, int UNUSED(x), int UNUSED(y)) {
             planetary_system->zoom_factor *= 1.1;
         } else {
             planetary_system->zoom_factor /= 1.1;
-
-            if (planetary_system->zoom_factor < 1) {
-                planetary_system->zoom_factor = 1;
-            }
         }
     }
 }
@@ -110,7 +109,6 @@ int main(int argc, char *argv[]) {
     glutSpecialFunc(handle_special_keyboard_input);
     glutMouseFunc(handle_mouse_input);
 
-    true_time_shift = time(NULL) % 1000;
     glutTimerFunc(1000 / REFRESH_RATE, update_timer, 0);
     glutTimerFunc(1000 / REFRESH_RATE, draw_timer, 0);