Martian

Monster data
HP	1
Points	200
Special	Bubbles players
Resists	-
Weak to	-

Entity data
Entity pointer	$81:99DF (normal) $81:9A3E (top of screen)

The martian is a respawning monster. Martians mainly use their bubble gun to attack, but can also hurt players and victims via contact damage. They aren't resistant or vulnerable to any weapon and are exclusively found in the grass tileset. They only have 1 hit point and award 200 points to the player when killed. There are two different types of martians: normal and top of screen.

Behavior

Normal martian

Normal martian behavior areas.
Red: Move away
Yellow: Line up
Pink: Move towards
Blue: Keep previous direction
Outside all colors: Despawn
Light area in center is the size of the screen

Normal martians will try to stay about 70 pixels away from a target, while lining themselves up for a shot on the target. However, the relatively large amount of time between direction updates means that they generally just dart around diagonally in the vicinity of the target.

• Every frame, attempt to shoot at a player or victim if there is one within 8 pixels of the martian on a single axis. Every 61 attempts, a shot will actually be fired.
  • When a shot is fired, stand in place for 12 frames.
• Every 61 frames (about once per second) update the movement direction:
  • If the nearest target is less than 60 pixels away, move away from the target.
  • If the nearest target is between 60 and 79 pixels away, move in the direction of the shortest distance to line up with the target on a single axis.
  • If the nearest target is between 80 and 223 pixels away, move towards the target.
  • If none of the above is true and there is no player within 207 pixels on a single axis, then despawn.
• Move in the current direction at a speed of 1.5 px/frame.

Top of screen martian

Top of screen martians will move side to side above a target, trying to maintain about 108 pixels of space vertically. Upon spawning, they will set their Y position to 8 pixels below the top of the screen.

• If there is no player within 207 pixels on a single axis, despawn.
• If there is a player above the martian, convert into a normal martian.
• Every frame, attempt to shoot at a player or victim if there is one within 8 pixels of the martian on a single axis. Every 61 attempts, a shot will actually be fired.
  • If a shot was not attempted in this way, randomly attempt to shoot down with probability 30/256 (about 11.72%).
  • When a shot is fired, stand in place for 12 frames.
• Every 33 frames, update horizontal movement direction:
  • If the nearest target is less than 32 pixels away, move away from the target.
  • If the nearest target is 32 pixels or more away, move towards the target.
• Move based on the current horizontal movement direction:
  • If the nearest target is less than 96 pixels below the martian, move up-left or up-right at a speed of 3 px/frame.
  • If the nearest target is between 96 and 119 pixels below the martian, move left or right at a speed of 1.5 px/frame.
  • If the nearest target is 120 pixels or more below the martian, move down-left or down-right at a speed of 3 px/frame.

Note that both types of martians will target decoys, but will not attempt to shoot at them.

Animation

WIP.

Bugs

• Freezing or bubbling a martian, then letting it despawn will count as killing it. This will increase their kill count in the final tally and award the player the corresponding amount of points. This is because the logic that determines if a martian was killed or not checks if it was ever hit by a weapon, not if it lost all its HP.
• Top of screen martians check if their updated spawn location is solid, and immediately despawn if it is. However, this check only looks for tiles that are solid to players, not solid to monsters. So, if the martian starts on a tile that is solid to monsters, but not players, it will be allowed to spawn, but will be unable to move.

Trivia

• There are 55 normal martian spawners and 20 top of the screen martian spawners in the game.
• Shooting martians 10 times with the martian bubble gun will award the player with the martian bubbled bonus. Strangely, this bonus is only enabled in level 41.
• The official manual mentions that martians hate tomatoes, but this isn't reflected in-game in any way.
• The martian design is likely based on the aliens from the 1957 movie Invasion of the Saucer Men.

RAM map

Entity arguments

Address	Length	Type	Name	Description
$00	2	int16	x	X position
$02	2	int16	y	Y position

Entity memory

Address	Length	Type	Name	Description
$08	2	pointer16	sprite	Pointer to sprite
$0A	2	pointer16	state	Current state subroutine pointer
$0C	2	int16	x	X position
$0E	2	int16	y	Y position
$10	2	int16	newX	New X position
$12	2	int16	newY	New Y position
$14	2	pointer16	spriteTable	Pointer to sprite table
$16	2	pointer16	targetSprite	Pointer to target sprite
$18	2	uint16	targetDistance	Distance to target
$1A	2	unused		Unused
$1C	2	int16	targetXOffset	Target sprite X offset from martian
$1E	2	int16	targetYOffset	Target sprite Y offset from martian
$20	2	uint16	targetXDistance	Target sprite X distance from martian (absolute value of $1C)
$22	2	optional pointer16	shootHandler	'Shoot' subroutine pointer
$24	2	uint16 0-based	shotThrottle	Number of shot attempts until shot will be fired
$26	2	boolean	dead	Dead
$28	2	direction x2	direction	Current direction
$2A	2	int16 0-based	directionChangeTimer	Number of frames until direction update (normal state only)
$2C	2	uint16	animationFrame	Current animation frame
$2E	2	int16 0-based	framesUntilAnimUpdate	Number of frames until next animation frame
$30	2	sprite type	collidedSpriteType	Type of weapon shot sprite collided with
$32	2	int16 0-based	health	Health
$34	2	int16 0-based	framesUntilSideUpdate	Number of frames until target side update (top of screen only)
$36	2	direction x2	targetSide	Target side (left or right) (top of screen only)
$7E	2	int16 0-based	freezeTimer	Amount of time to stay frozen

Pseudocode

spriteTableDefault = { // $81:9969
	0xD66D, 0xD69E, 0xD6C7, 0xD6F8,
	0xD721, 0xD752, 0xD783, 0xD7B4,
	0xD7E5, 0xD816, 0xD847, 0xD878
}

shootHandlerDefault(direction) { // $81:9981
	bubbleGunShot.args.direction = direction
	bubbleGunShot.args.x = this.x
	bubbleGunShot.args.y = this.y
	bubbleGunShot.args.character = -1

	if (this.shotThrottle == 0) {
		this.shotThrottle = 60
		setSprite(shootSpriteIndexes[direction])
		if (direction < DOWN) {
			this.sprite.flipX = false
		} else {
			this.sprite.flipX = true
		}
		
		createEntity($81:F380)
		waitFrames(12)
	} else {
		this.shotThrottle -= 1
	}
}

shootSpriteIndexes = { 0, 8, 0, 0, 0, 4, 0, 0, 0 } // $81:99CD

main_Normal() { // $81:99DF
	$7E:00DE += 0x1E
	init()
	setStateToNormal()

	while (!this.dead) {
		waitFrames(1)
		this.state()
	}

	if (this.collidedSpriteType != 0) {
		givePoints(this.collidedSpriteType & 0x8000, 200)
		martiansKilled += 1
		showAnimation(deathAnimation_Normal)
	}

	$7E:00DE -= 0x1E
	while ($7E:00DE < 0) { }
	deleteSprite(this.sprite)
}

deathAnimation_Normal = { // $81:9A2A
	{ 0xD998, 5}, { 0xD96F, 5 }, { 0xD946, 5 }, { 0xDA2B, 5 },
	{ 0, 0 }
}

main_TopOfScreen() { // $81:9A3E
	if (tryToSpawnAtTopOfScreen()) {
		return
	}

	$7E:00DE += 0x1E
	init()
	setStateToTopOfScreen()

	while (!this.dead) {
		waitFrames(1)
		this.state()
	}

	if (this.collidedSpriteType != 0) {
		givePoints(this.collidedSpriteType & 0x8000, 200)
		martiansKilled += 1
		showAnimation(deathAnimation_TopOfScreen)
	}

	$7E:00DE -= 0x1E
	while ($7E:00DE < 0) { }
	deleteSprite(this.sprite)
}

deathAnimation_TopOfScreen = { // $81:9A8E
	{ 0xD998, 5}, { 0xD96F, 5 }, { 0xD946, 5 }, { 0xDA2B, 5 },
	{ 0, 0 }
}

tryToSpawnAtTopOfScreen() { // $81:9AA2
	args.Y = cameraY + 8
	return bgSolidToPlayers(args.x, args.y) || outsideOfLevel(args.x, args.y)
}

init() { // $81:9AC0
	this.sprite = createSprite()
	this.x = args.x
	this.sprite.x = args.x
	this.sprite.z = 0
	this.y = args.y
	this.sprite.y = args.y
	this.sprite.tileData = $90:D66D
	this.sprite.entity = currentEntity
	this.sprite.type = MONSTER
	this.sprite.visible = true
	this.sprite.alternatePalette = 6
	this.sprite.type = MONSTER

	this.shotThrottle = 0
	this.animationFrame = 0
	this.framesUntilAnimUpdate = 0
	this.shootHandler = null
	this.dead = false
	this.directionChangeTimer = 0
	this.freezeTimer = 0
	this.collidedSpriteType = 0
	this.health = 0

	this.setShootHandler(shootHandlerDefault)
	this.setSpriteTable(spriteTableDefault)
	showAnimation(spawnAnimation)
	setCollisionHandler(collisionHandler)
}

spawnAnimation = { // $81:9B3B
	{ 0xD8BA, 6 }, { 0xD8D3, 6 }, { 0xD8F4, 6 }, { 0xD91D, 6 }
	{ 0xD946, 6 }, { 0xD96F, 6 }, { 0xD998, 6 }, { 0xD9C9, 4 }
	{ 0xD9FA, 4 }, { 0xDA2B, 4 }, { 0xD66D, 1 }, { 0, 0 }
}

collisionHandler(spriteType) { // $81:9B6B
	if (spriteType < SQUIRT_GUN) {
		return false
	}
	this.collidedSpriteType = spriteType

	weaponType = spriteType & 0x7FFF
	if (weaponType == MARTIAN_BUBBLE_GUN) {
		martiansBubbled[playerForCharacter((spriteType & 0x8000) >> 15)] += 1
		return bubbleMonster()
	} else if (weaponType == FIRE_EXTINGUISHER) {
		return freezeMonster()
	} else {
		newHealth = this.health - weaponDamage[weaponType - SQUIRT_GUN]
		if (newHealth < 0) {
			this.dead = true
			this.health = newHealth
			this.freezeTimer = 0
			return true
		} else if (newHealth != this.health) {
			this.health = newHealth
			return showDamageAnimation()
		}
		return false
	}
}

setSpriteTable(spriteTable) { // $81:9B6B
	this.spriteTable = spriteTable
}

setShootHandler(shootHandler) { // $81:9BBD
	this.shootHandler = shootHandler
}

getDirectionToLineUpWithTarget() { // $81:9BC0
	this.targetXDistance = abs(this.targetXOffset)
	if (this.targetXDistance <= abs(this.targetYOffset)) {
		if (this.targetXOffset == 0) {
			return NONE
		} else if (this.targetXOffset < 0) {
			return LEFT
		} else {
			return RIGHT
		}
	} else {
		if (this.targetYOffset == 0) {
			return NONE
		} else if (this.targetYOffset < 0) {
			return UP
		} else {
			return DOWN
		}
	}
}

move(direction) { // $81:9BF3
	if (frameCounter % 4 == 0) {
		return
	}

	this.newX = this.x + moveAmount[direction][0]
	this.newY = this.y + moveAmount[direction][1]

	if (!bgSolidToMonsters(this.newX, this.y) &&
	    !outsideOfLevel(this.newX, this.y) &&
	    !touchingSpriteSolidToMonsters(this.sprite, this.newX, this.y)) {
		this.x = this.newX
	}
	if (!bgSolidToMonsters(this.x, this.newY) &&
	    !outsideOfLevel(this.x, this.newY) &&
	    !touchingSpriteSolidToMonsters(this.sprite, this.x, this.newY)) {
		this.y = this.newY
	}
	this.sprite.x = this.x
	this.sprite.y = this.y
}

moveAmount = { // $81:9C62
	{  0,  0 },
	{  0, -2 },
	{  2, -2 },
	{  2,  0 },
	{  2,  2 },
	{  0,  2 },
	{ -2,  2 },
	{ -2,  0 },
	{ -2, -2 }
}

oppositeDirection = { NONE, DOWN, DOWN_LEFT, LEFT, UP_LEFT, UP, UP_RIGHT, RIGHT, DOWN_RIGHT } // $81:9C86

setSprite(index) { // $81:9C8F
	this.sprite.tileData.lowBytes = this.spriteTable[index]
}

updateAnimation_Normal() { // $81:9C99
	index = walkingAnimations[this.direction][this.animationFrame]
	if (index >= 12) {
		index = 8
	}

	setSprite(index)
	if (this.direction < DOWN) {
		this.sprite.flipX = false
	} else {
		this.sprite.flipX = true
	}

	this.framesUntilAnimUpdate -= 1
	if (this.framesUntilAnimUpdate < 0) {
		this.framesUntilAnimUpdate = 4
		this.animationFrame = (this.animationFrame + 1) % 4
	}
}

walkingAnimations = { // $81:9CD7
	{ 4,  5,  6,  7  },
	{ 8,  9,  10, 11 },
	{ 0,  1,  2,  3  },
	{ 0,  1,  2,  3  },
	{ 0,  1,  2,  3  },
	{ 4,  5,  6,  7  },
	{ 0,  1,  2,  3  },
	{ 0,  1,  2,  3  },
	{ 0,  1,  2,  3  }
}

shoot(direction) { // $81:9D1F
	if (this.shootHandler != null) {
		this.shootHandler(direction)
	}
}

setStateToNormal() { // $81:9D2A
	this.state = normalState
}

normalState() { // $81:9D30
	direction = findShootDirection(this.x, this.y)
	if (direction != NONE) {
		shoot(direction)
	}

	this.directionChangeTimer -= 1
	if (this.directionChangeTimer < 0) {
		this.directionChangeTimer = 60

		this.targetDistance, this.targetSprite, this.targetXOffset, this.targetYOffset =
		    findTarget(this.x, this.y)
		if (this.targetDistance < 60) {
			snapToTarget(this.sprite, this.targetSprite)
			this.direction = oppositeDirection[getDirectionToTarget(this.sprite, this.targetSprite)]
		} else if (this.targetDistance < 80) {
			this.direction = getDirectionToLineUpWithTarget()
		} else if (this.targetDistance < 224) {
			snapToTarget(this.sprite, this.targetSprite)
			this.direction = getDirectionToTarget(this.sprite, this.targetSprite)
		} else {
			direction = findPlayerInRangeDirection(208, this.x, this.y)
			if (direction == NONE) {
				this.dead = true
			}
			return
		}
	}

	move(this.direction)
	updateAnimation_Normal()
}

setStateToTopOfScreen() { // $81:9DB1
	this.state = topOfScreenState
	this.framesUntilSideUpdate = 0
	this.targetSide = 0
}

topOfScreenState() { // $81:9DBB
	direction = findPlayerInRangeDirection(208, this.x, this.y)
	if (direction == NONE) {
		this.dead = true
	}

	if (anyPlayerAbove()) {
		this.animationFrame = 0
		this.framesUntilAnimUpdate = 0
		setStateToNormal()
		return
	}

	direction = findShootDirection(this.x, this.y)
	if (direction != NONE) {
		shoot(direction)
	} else if (getRandomByte() < 30) {
		shoot(DOWN)
	}

	this.framesUntilSideUpdate -= 1
	if (this.framesUntilSideUpdate < 0) {
		this.framesUntilSideUpdate = 32

		this.targetDistance, this.targetSprite = findTarget(this.x, this.y)
		if (this.targetDistance < 32) {
			snapToTarget(this.sprite, this.targetSprite)
			direction = oppositeDirection[getDirectionToTarget(this.sprite, this.targetSprite)]
		} else {
			snapToTarget(this.sprite, this.targetSprite)
			direction = getDirectionToTarget(this.sprite, this.targetSprite)
		}
		this.targetSide = direction < DOWN ? RIGHT : LEFT
	}

	this.direction = this.targetSide
	targetYDistance = abs(this.targetSprite.y - this.y)
	if (targetYDistance < 96) {
		this.direction = this.targetSide < DOWN ? UP_RIGHT : UP_LEFT
		moveTopOfScreen()
	} else if (targetYDistance >= 120) {
		this.direction = this.targetSide < DOWN ? DOWN_RIGHT : DOWN_LEFT
		moveTopOfScreen()
	}
	moveTopOfScreen()
}

moveTopOfScreen() { // $81:9E40 (this is in the middle of code that is part of the above subroutine)
	move(this.direction)
	updateAnimation_TopOfScreen()
}

updateAnimation_TopOfScreen() { // $81:9E8D
	this.framesUntilAnimUpdate -= 1
	if (this.framesUntilAnimUpdate < 0) {
		this.framesUntilAnimUpdate = 4

		this.animationFrame = (this.animationFrame + 1) % 4
		setSprite(topOfScreenAnimation[this.animationFrame])
	}
}

topOfScreenAnimation = { 4, 5, 6, 7 } // $81:9EA7

anyPlayerAbove() { // $81:9EAF
	if (playerSprites[0] != null && playerSprites[0].y < this.y) {
		return true
	}
	if (playerSprites[1] != null && playerSprites[1].y < this.y) {
		return true
	}
	return false
}