Defender (Eugene Jarvis and Sam Dicker's 6809 source)

Defender moves its ship once per video frame: the interrupt calls the player routine once each time the beam passes line 128. Each call damps the horizontal velocity by 1/64 of itself, then a held thrust button adds 3/256 of a velocity unit in the facing direction (reverse negates it), and the velocity is held to ±1 unit. A unit is 256 world units, 8 pixels, a frame (the world has 32 units to a pixel). Since the damping runs every frame, thrust alone levels off at 3 × 64 = 192/256 of a unit, 6 pixels a frame, below the cap (computed). The source is the Red Label release. defender/thrust

About: Defender Inertia

{
 "damping": 0.015625,
 "thrust": 3,
 "cap": 256,
 "thrustTop": 192
}

The ship's place on the screen also slides toward a point set by its direction and speed (PLAY1-PV10), with the scroll making up the difference; this claim doesn't cover that.

Cited by: Defender, Inertia

Up and down have no inertia in Defender: a held direction moves the ship 1 pixel a frame at once, rising by 8/256 of a pixel each frame to 2 pixels a frame (after 32 frames, computed), and letting go stops it. The ship stops climbing once at row 43 or higher, and descending at row 238 or lower. defender/vertical

About: Defender Inertia

{
 "start": 256,
 "step": 8,
 "max": 512
}

Down is the mirror of up (PLADN-PLADN1).

Cited by: Defender

Defender's world is a loop: objects keep 16-bit X world coordinates, 32 units to a pixel, so the world is 65,536 units, 2,048 pixels, around and joins itself through 16-bit overflow (computed). Objects off the screen also wrap from the bottom (row 240) to the top (row 42) and back. defender/world

About: Defender Screen wrap

Value: 2048 pixels around (computed)

The vertical wrap read here is the off-screen update's; on-screen objects move elsewhere (VELO), not read for this claim.

Cited by: Defender, Screen wrap

Defender's scanner draws every object, on the active and the inactive list alike, as a blip. Its left edge sits half the world (less 150 pixels) behind the screen's left edge, so the view stays at the scanner's middle. An object's offset from that edge, cut to its top 6 bits, and its row divided by 8 give the blip's screen address: 64 places across the whole world (computed). defender/scanner

About: Defender Minimap

Value: 64 places across the world (computed)

The source's OPTR list holds objects near the screen and IPTR the rest (OSCAN, ISCAN).

Cited by: Defender, Minimap

A smart bomb works when none is already going off and the player has one left: it takes one and runs the collision routine of every active object that is on the screen and of type 0 or 1 (normal objects and landers picking someone up), destroying them. Objects of type 2 and up are skipped, among them the humanoids, type $10, "NON SMART BOMB". Players start with as many smart bombs as ships. defender/smart-bomb

About: Defender Smart bomb

The screen then flashes (SBMBX) and the bomb button must be let go before another.

Cited by: Defender, Smart bomb

Hyperspace works only in normal play (status bits other than the no-terrain bit clear). It clears the screen, removes the bullets, moves the view to a random place in the world, faces the ship a random way, sets a random height, and zeroes the ship's velocity. After the ship reappears and a pause, it dies if a random byte is above 192: 63 of 256 values, about 1 jump in 4 (computed). defender/hyperspace

About: Defender Hyperspace

{
 "deadly": 63,
 "of": 256
}

The count assumes LSEED's values are evenly spread; the random routine isn't read here.

Cited by: Defender, Hyperspace

A Defender lander picks a humanoid from the target list and heads for it. Over it, the lander descends, grabs it, and climbs with it; at the top of the play area it pulls the humanoid inside, which kills the humanoid, and the lander becomes a mutant ("SCHITZO" in the source). Shooting a lander that carries a humanoid starts the humanoid falling. defender/kidnap

About: Defender Rescue

A falling humanoid's outcomes are defender/rescue.

Cited by: Defender

When the last humanoid dies, Defender blows up the planet's terrain. With no humanoids left, a lander that looks for a new target becomes a mutant, and new landers start as mutants. By the operator default, every fifth wave restores the humanoids to 10, the number each player starts with. defender/planet

About: Defender Rescue

{
 "humanoids": 10,
 "restoreEvery": 5
}

STCHK keeps the no-terrain status bit set while the humanoid count is 0.

Cited by: Defender

A dropped humanoid falls faster each step, up to a limit. Touching it with the ship scores 500 and carries it under the ship, and setting it down on the ground scores 500 more. Left alone, it lands for 250 if its fall speed is $E0 or less, and dies if faster. At the end of each wave, each humanoid left scores 100 times the wave number, at most 500 (computed from the score calls). defender/rescue

About: Defender Rescue

{
 "catch": 500,
 "setDown": 500,
 "landAlone": 250,
 "waveBonusMax": 500
}

AFALL caps the fall speed at $300 by not storing larger values. A shot humanoid dies (AKIL10).

Cited by: Defender, Rescue

Defender reads each wave's enemies from a table with a column for each of waves 1 to 4: landers 15, 20, 20, 20; bombers 0, 3, 4, 5; pods 0, 1, 3, 4; no mutants or swarmers at the start; landers come in groups of 5. Later waves take the fourth column plus per-wave increments, which are 0 for these counts, so they keep the fourth wave's numbers (computed). defender/waves

About: Defender Difficulty ramp

{
 "landers": [
  15,
  20,
  20,
  20
 ],
 "bombers": [
  0,
  3,
  4,
  5
 ],
 "pods": [
  0,
  1,
  3,
  4
 ],
 "group": 5
}

The bomber count is above its row's maximum of 3 from wave 2; WDELT skips the store when a sum passes the maximum, so it stays as read from the column. Speeds and timers in the same table do rise with the deltas.

Cited by: Defender, Difficulty ramp

Defender gives an extra ship and an extra smart bomb at each replay level: the level starts at the replay setting and rises by it each time it is passed. The operator default is 10,000 points, with 3 ships to a game. defender/replay

About: Defender Extra life

Value: 10000 points per replay (operator default)

A replay setting of 0 turns replays off (the BEQ at SCRX).

Cited by: Defender, Extra life