95 lines
3.3 KiB
GDScript3
95 lines
3.3 KiB
GDScript3
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class_name CelestialBody
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extends RigidBody2D
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# The celestial body that this body orbits.
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@export var primary: CelestialBody
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# Real-world gravitational constant.
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const G_REAL = 6.674e-11
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# This is a placeholder for your pixel art texture.
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@export var texture: Texture2D
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# The radius of the body, used for drawing and future collision detection.
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@export var radius: float = 10.0
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# Real-world mass of the body in kilograms.
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@export_range(1.0, 1.989e+30, 1.0, "exp") var mass_real: float = 1.0
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# The scaling factor for the simulation. A value of 1.0 means no scaling.
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var sim_scale: float = 1.0
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# Default color based on body type for visualization.
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var body_color: Color = Color.ORANGE_RED
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func get_class_name() -> String:
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return "CelestialBody"
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func _ready() -> void:
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# Set the scaled mass based on the real-world mass and the simulation scale.
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# The scale is applied to the mass, so a smaller scale means a larger apparent mass.
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mass = mass_real / (sim_scale * sim_scale)
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# We will handle gravity manually, so we set the built-in gravity scale to 0.
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gravity_scale = 0.0
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# To make the simulation work without drag, we must set linear damping to 0.
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linear_damp = 0.0
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# Set the color based on the class name for easy differentiation.
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match get_class_name():
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"Star":
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body_color = Color.GOLD
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"Planet":
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body_color = Color.BLUE
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"Moon":
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body_color = Color.PURPLE
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"Station":
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body_color = Color.WHITE
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"Asteroid":
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body_color = Color.BROWN
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_:
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body_color = Color.ORANGE_RED
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# This callback is the correct place to apply custom forces to a RigidBody2D.
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func _integrate_forces(state: PhysicsDirectBodyState2D) -> void:
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if primary and is_instance_valid(primary):
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# Get the vector pointing from this body to its primary.
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var direction_to_primary = primary.global_position - state.transform.origin
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var distance_squared = direction_to_primary.length_squared()
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# Prevent division by zero or a large force if bodies are on top of each other.
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if distance_squared > 1.0:
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# Calculate the magnitude of the gravitational force using Newton's law.
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# We now use the scaled masses, which is consistent with Godot's physics engine.
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# F = G * (m1 * m2) / r^2
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var force_magnitude = (G_REAL * self.mass * primary.mass) / distance_squared
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# Apply the force in the direction of the primary.
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state.apply_central_force(direction_to_primary.normalized() * force_magnitude)
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# We force a redraw here to update the body's visual representation.
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queue_redraw()
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# Override the default drawing function to draw the body.
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# This is useful for debugging and visualization.
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func _draw() -> void:
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if texture:
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# If a texture is assigned, draw it.
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var size = Vector2(radius * 2, radius * 2)
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var offset = -size / 2.0
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draw_texture_rect(texture, Rect2(offset, size), false)
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else:
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# Otherwise, draw a simple placeholder circle.
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draw_circle(Vector2.ZERO, radius, body_color)
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# Calculates the velocity required for a stable circular orbit.
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func get_stable_orbit_velocity(primary_mass_real: float, distance_real: float) -> float:
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# The formula for real-world orbital velocity is v = sqrt(G * M / r)
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var real_world_velocity = sqrt((G_REAL * primary_mass_real) / distance_real)
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# Scale this velocity down to the simulation scale before returning.
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return real_world_velocity / sim_scale
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