Add planetary masses.

CMakeLists.txt

@@ -44,6 +44,7 @@ include_directories(
 set(SRCS
 	src/event_manager.c
 	src/main.c
+	src/planet.c
 	src/ship.c
 	src/starfield.c)
 

TODO

@@ -1,2 +0,0 @@
-TODO:
- - Add presets with stellar masses (for gravity simulation).

src/globals.h

@@ -26,7 +26,7 @@
 #	define FPS 60.0f
 #endif
 #ifndef ACCEL
-#	define ACCEL 0.1f
+#	define ACCEL 0.3f
 #endif
 #ifndef TURN_ACCEL
 #	define TURN_ACCEL (M_PI / FPS)  // turn at pi radians / sec

src/main.c

@@ -20,6 +20,7 @@
 #include "event_manager.h"
 #include "ship.h"
 #include "starfield.h"
+#include "planet.h"
 
 int run;
 int redraw;
@@ -106,6 +107,10 @@ int main() {
 	struct ship ship;
 	ship_init(&ship, 400, 300);
 
+	// initialize the planet
+	struct planet planet;
+	planet_init(&planet, 400.0f, 300.0f, 250.0f);
+
 	ALLEGRO_FONT *font = al_create_builtin_font();
 
 	// begin running the simulation
@@ -140,7 +145,11 @@ int main() {
 				if(key_is_down(KEY_RESET))
 					ship_init(&ship, (float)WINDOW_WIDTH / 2, (float)WINDOW_HEIGHT / 2);
 				else
-					ship_update(&ship);
+				{
+					float gravity_x, gravity_y;
+					planet_get_gravity(&planet, ship.x, ship.y, &gravity_x, &gravity_y);
+					ship_update(&ship, gravity_x, gravity_y);
+				}
 			}
 
 			if (key_is_down(KEY_FULLSCREEN) && !just_toggled_fullscreen)
@@ -190,6 +199,7 @@ int main() {
 			al_use_transform(&transform);
 
 			starfield_draw(ship.x, ship.y, zoom, display_width, display_height);
+			planet_draw(&planet);
 			ship_draw(&ship);
 
 			al_identity_transform(&transform);

src/planet.c

@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2026  Ortega Froysa, Nicolás <nicolas@ortegas.org>
+ * Author: Ortega Froysa, Nicolás <nicolas@ortegas.org>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "planet.h"
+#include <math.h>
+#include <assert.h>
+#include <allegro5/allegro_primitives.h>
+
+#define GRAVITY_CONSTANT 1.0f  // Gravitational constant scaled for simulation
+#define SHIP_MASS 1.0f           // Assumed constant ship mass
+#define MASS_TO_RADIUS 1.5f      // Radius scale factor: radius = MASS_TO_RADIUS * mass^(1/3)
+
+void planet_init(struct planet *planet, float x, float y, float mass) {
+	assert(planet);
+
+	planet->x = x;
+	planet->y = y;
+	planet->mass = mass;
+	planet->radius = MASS_TO_RADIUS * cbrtf(planet->mass);
+}
+
+void planet_get_gravity(struct planet *planet, float ship_x, float ship_y,
+						float *accel_x, float *accel_y) {
+	assert(planet);
+	assert(accel_x);
+	assert(accel_y);
+
+	float dx = planet->x - ship_x;
+	float dy = planet->y - ship_y;
+	float distance = sqrtf(dx * dx + dy * dy);
+
+	if(distance < planet->radius) {
+		*accel_x = 0.0f;
+		*accel_y = 0.0f;
+		return;
+	}
+
+	// F = G * m1 * m2 / r^2
+	float force = GRAVITY_CONSTANT * SHIP_MASS * planet->mass / (distance * distance);
+
+	// a = F / m_ship = G * m_planet / r^2
+	float acceleration = force / SHIP_MASS;
+
+	// Normalize direction and apply acceleration
+	float norm_x = dx / distance;
+	float norm_y = dy / distance;
+
+	*accel_x = norm_x * acceleration;
+	*accel_y = norm_y * acceleration;
+}
+
+void planet_draw(struct planet *planet) {
+	assert(planet);
+
+	// Color intensity based on mass (brighter = more massive)
+	float color_scale = fminf(1.0f, planet->mass / 1000.0f);
+	int r = (int)(100 + 155 * color_scale);
+	int g = (int)(100 + 50 * color_scale);
+	int b = (int)(150 - 100 * color_scale);
+
+	al_draw_filled_circle(planet->x, planet->y, planet->radius,
+			al_map_rgb(r, g, b));
+}

src/planet.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2026  Ortega Froysa, Nicolás <nicolas@ortegas.org>
+ * Author: Ortega Froysa, Nicolás <nicolas@ortegas.org>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+/**
+ * Function pointer type for calculating planet mass.
+ * Takes no parameters and returns the mass value.
+ */
+typedef float (*planet_mass_func)(void);
+
+struct planet {
+	float x, y;       ///< The x and y coordinates of the planet center.
+	float mass;       ///< The mass of the planet.
+	float radius;     ///< The radius of the planet (derived from mass).
+};
+
+/**
+ * @brief Initialize a planet at a position with a specified mass.
+ *
+ * @param planet A pointer to the planet object.
+ * @param x Initial x position of the planet center.
+ * @param y Initial y position of the planet center.
+ * @param mass The mass of the planet.
+ */
+void planet_init(struct planet *planet, float x, float y, float mass);
+
+/**
+ * @brief Calculate the gravitational acceleration on a ship at a given position.
+ *
+ * Returns the acceleration vector components due to the planet's gravity.
+ *
+ * @param planet A pointer to the planet object.
+ * @param ship_x X position of the ship.
+ * @param ship_y Y position of the ship.
+ * @param accel_x Pointer to store the x component of acceleration.
+ * @param accel_y Pointer to store the y component of acceleration.
+ */
+void planet_get_gravity(struct planet *planet, float ship_x, float ship_y,
+						float *accel_x, float *accel_y);
+
+/**
+ * @brief Draw the planet.
+ *
+ * @param planet Planet object to draw.
+ */
+void planet_draw(struct planet *planet);

src/ship.c

@@ -34,7 +34,7 @@ void ship_init(struct ship *ship, float x, float y) {
 	ship->direction = 0;
 }
 
-void ship_update(struct ship *ship) {
+void ship_update(struct ship *ship, float gravity_x, float gravity_y) {
 	assert(ship);
 
 	if(key_is_down(KEY_RIGHT))
@@ -60,6 +60,10 @@ void ship_update(struct ship *ship) {
 		ship->velY -= sin(ship->direction) * (ACCEL / 2);
 	}
 
+	// Apply gravitational acceleration
+	ship->velX += gravity_x;
+	ship->velY += gravity_y;
+
 	ship->x += ship->velX;
 	ship->y += ship->velY;
 }

src/ship.h

@@ -41,11 +41,13 @@ void ship_init(struct ship *ship, float x, float y);
 
 /**
  * @brief Updates the ship's variables according to keyboard
- * input.
+ * input and gravitational forces.
  *
  * @param ship A pointer to the ship object.
+ * @param gravity_x Gravitational acceleration in x direction.
+ * @param gravity_y Gravitational acceleration in y direction.
  */
-void ship_update(struct ship *ship);
+void ship_update(struct ship *ship, float gravity_x, float gravity_y);
 
 /**
  * @brief Draw the ship.