Gravity well

References

1. ^ abcA Melee planet is an element with 200 hit points and a mass of 200, above GRAVITY_MASS's threshold of 100 (10 times MAX_SHIP_MASS), whose per-frame postprocess is CalculateGravity. That routine pulls every other colliding element without such mass that lies within 255 display units of the planet (GRAVITY_THRESHOLD, tested on each axis and then as a radius, measured the short way across the arena's wrapped edges): it adds 1 world unit per frame to the element's velocity, aimed at the planet, whatever the distance, and flags a ship as in a gravity well. A block under #ifdef NEVER, never compiled, works out a pull from the distance, capped at 6, and only prints it.CodeThe Ur-Quan Masters (2002 import)
   How we know

   22spawn_planet (void)
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   34		PlanetElementPtr->hit_points = 200;
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   42		PlanetElementPtr->postprocess_func =
   43				(void (*) (struct element *ElementPtr))CalculateGravity;
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   54		PlanetElementPtr->mass_points = PlanetElementPtr->hit_points;
   

   131#define MAX_SHIP_MASS 10
   132#define GRAVITY_MASS(m) ((m) > MAX_SHIP_MASS * 10)
   133#define GRAVITY_THRESHOLD (COUNT)255
   

   28	HasGravity = (BOOLEAN)(CollidingElement (ElementPtr)
   29			&& GRAVITY_MASS (ElementPtr->mass_points + 1));
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   38				&& CollidingElement (TestElementPtr)
   39				&& (TestHasGravity =
   40				GRAVITY_MASS (TestElementPtr->mass_points + 1)) != HasGravity)
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   66			dx = WRAP_DELTA_X (dx);
   67			dy = WRAP_DELTA_Y (dy);
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   74			abs_dx = WORLD_TO_DISPLAY (abs_dx);
   75			abs_dy = WORLD_TO_DISPLAY (abs_dy);
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   80			if (abs_dx <= GRAVITY_THRESHOLD
   81					&& abs_dy <= GRAVITY_THRESHOLD)
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   87				if (dist_squared <= (DWORD)(GRAVITY_THRESHOLD
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   131#define WRAP_DELTA_X(dx) ((dx)<0 ? \
   132				((-(dx)<=LOG_SPACE_WIDTH>>1)?(dx):(LOG_SPACE_WIDTH+(dx))) : \
   

   Checked against the evidence by its author, an AI model, 2026-10-22.

   Checked by a second AI model, 2026-10-22.

   In the claim ledger

2. ^inertial_thrust caps the speed itself, not each axis: after adding a thrust step it compares the sum of the squared components with MAX_THRUST squared, so a ship is no faster on a diagonal. Asteroids clamps each axis of its ship's velocity apart, so its diagonal is faster (asteroids/top-speed). A step that would pass the cap still applies if the result is slower than the current speed. At the cap, a step along the line of travel sets the velocity to exactly MAX_THRUST along the facing (if the ship isn't above the cap); a step off the line instead adds half a thrust step along the facing and takes a whole step off along the line of travel, kept if that ends within the cap or slower than before, so the course swings toward the facing. While the ship is flagged in a gravity well, a thrust step may take it past the cap up to MAX_ALLOWED_SPEED, 18 display units per frame.CodeThe Ur-Quan Masters (2002 import) · Computer Archeology, Asteroids
   How we know

   75		desired_speed = (DWORD)((long)delta_x * delta_x)
   76				+ (DWORD)((long)delta_y * delta_y);
   77		max_speed = (DWORD)WORLD_TO_VELOCITY (max_thrust)
   78				* WORLD_TO_VELOCITY (max_thrust);
   79		if (desired_speed <= max_speed)
   80			SetVelocityComponents (VelocityPtr, delta_x, delta_y);
   81		else
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   83#define MAX_ALLOWED_SPEED WORLD_TO_VELOCITY (DISPLAY_TO_WORLD (18))
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   86			if (((StarShipPtr->cur_status_flags & SHIP_IN_GRAVITY_WELL)
   87					&& desired_speed <=
   88					(DWORD)MAX_ALLOWED_SPEED * (DWORD)MAX_ALLOWED_SPEED)
   89					|| (current_speed =
   ⋮
   

   56	else if ((TravelAngle =
   57			GetVelocityTravelAngle (VelocityPtr)) == CurrentAngle
   58			&& (StarShipPtr->cur_status_flags
   59			& (SHIP_AT_MAX_SPEED | SHIP_BEYOND_MAX_SPEED))
   60			&& !(StarShipPtr->cur_status_flags & SHIP_IN_GRAVITY_WELL))
   

   BMI $7130 ; {} CMP #$40 BCC $7138 ; {} LDX #$FF LDA #$3F RTS CMP #$C0 BCS $7138 ; {} LDX #$01 LDA #$C0

   Checked against the evidence by its author, an AI model, 2026-10-22.

   Checked by a second AI model, 2026-10-22.

   In the claim ledger