TASVideos

Tool-assisted game movies
When human skills are just not enough

Game Resources / NES / Ninja Gaiden

Address Description
0060
0061
Score, little endian. Game can only display 4 digits; "00" on the right of score display is static.
0062 Timer fractions. Cycles 60-0, normally decrementing once per frame during game play.
0063 Level Timer. Decrements when $0062 = 60.
0064 Ninpo (Points used for special attacks)
0065 Ryu's Hit Points
0066 Enemy HP Display (separate from actual enemy HP, stored at $0490-0497)
0067-006C Level Scrolling
006D
006E
Current Stage
006F Related to stage transitions
0075 TODO: explain this
0076 Ryu's Lives
0080-0083 Ryu's Animations
0084 Ryu's facing and state (standing/jumping/clinging to wall/etc.)
0085 Ryu's x position, fractions
0086 Ryu's x position, pixels
0087 Ryu's y speed, fractions
0089 Ryu's y speed, pixels
008A Ryu's y position
0092 0x00 until Ryu uses his sword, after which it is 0x10, meaning the first sword attack after the game starts is always ineffective. First jumping slash after having used Spin Slash also affected.
0095 Invulnerability timer, runs 60-0 starting when Ryu takes damage.
0096-009F pointers
00A2 Screen position, fractions
00A3 Screen position, pixels
00AC Ryu's x speed, fractions
00AD Ryu's x speed, pixels
00B5 Object spawn iterator (increments 8 times a frame)
00BF Global Timer
00C9 Current Special Weapon.
$00=None
$80=Art of the Fire Wheel
$81=Throwing Star
$82=Windmill Star
$84=Invincible Fire Wheel
$85=Jump and Slash
02xx Sprite Data
03xx Background Data
0400-0407 Enemy ID
0408-040F Frames until enemy action (changing direction, throwing/shooting stuff)
0438-043F Enemy movement
0440-0447 Enemy facing (left/right)
0448-044F Enemy x speed, fractions
0450-0457 Enemy x speed, pixels
0458-045F Enemy x position, fractions
0460-0467 Enemy x position, pixels
0468-046F Enemy y speed, fractions
0470-0477 Enemy y speed, pixels
0478-047F Enemy y position, fractions
0480-0487 Enemy y position, pixels
0490-0497 Enemy hit points (only non-zero for bosses and those grey disc-tossers)
04B8-04BA Boss Explosion Animations
04BB Spec. Weapon C x position
04BC Spec. Weapon B x position
04BD Spec. Weapon A x position
04BE Spec. Weapon C y position
04BF Spec. Weapon B y position
04C0 Spec. Weapon A y position
04C1-04C6 Spec. Weapon Speed (used differently for each weapon)
04C7 Spec. Weapon time-out, fractions (hourglass, invincible fire wheel)
04C8 Spec. Weapon time-out (hourglass, invincible fire wheel)
04D0-04D7 Lantern(or bug or bird)/Power-Up x position, fractions
04D8-04DF Lantern/PU x position, pixels
04E0-04E7 Lantern/PU y position, pixels (no fractions for this)
04E8-04EF Frames until power-up vanishes
05xx Unused
06xx Sound

--Displays most of the RAM addresses relevant to making a TAS over or around the game's info display.
local function NGRAMview()
  yspd = memory.readbytesigned(0x89) + (memory.readbyte(0x87)/256)
  xpos = memory.readbyte(0x86) + (memory.readbyte(0x85)/256)
  ypos = memory.readbyte(0x8A)
  scrnpos = memory.readbyte(0xA3); scrnsub = memory.readbyte(0xA2)
  timerf = memory.readbyte(0x62); timer = memory.readbyte(0x63)
  rnga = memory.readbyte(0xB5); rngb = memory.readbyte(0xBF)
  ninpo = memory.readbyte(0x64)
  bosshp = memory.readbyte(0x497); abosshp = memory.readbyte(0x496)
  inv = memory.readbyte(0x95)
  gui.text(25,9,string.format("Y-Spd:%6.3f",yspd))
  gui.text(25,17,string.format("Position: %5.1f, %3d",scrnpos+xpos+(scrnsub/256),ypos))
  gui.text(129,17,string.format("[%05.1f+%02X,%02X]",xpos,scrnpos,scrnsub))
  gui.text(73,33,string.format("%3d:%02d",timer,timerf))
  if bosshp > 0 then
   if bosshp > 16 then gui.text(177,41,string.format("%02d",abosshp))
    else gui.text(177,41,string.format("%02d",bosshp)); end; end
  if inv > 0 then
   gui.text(229,33,string.format("%02d",inv));end
  gui.text(208,17,string.format("B5:%3d ",rnga))
  gui.text(208,25,string.format("BF:%3d ",rngb))
  gui.text(81,41,string.format("[%02d]",ninpo))
end
gui.register(NGRAMview)
emu.frameadvance()
--Accurately tracks the game's inaccurate conception of time, displaying how many "seconds" elapse over the course of a game session.
--Obviously, it is not smart enough to account for save states, but here it is in case somebody finds this interesting.
local minutes=0;seconds=0;frames=0
while true do
 prevt = memory.readbyte(0x62)
 emu.frameadvance()
 currt = memory.readbyte(0x62)
 if prevt ~= currt then
  frames=frames+1;end
 if frames == 61 then
  seconds=seconds+1;frames=0;end
 if seconds == 60 then
  minutes=minutes+1;seconds=0;end
 gui.text(199,9,string.format("%02d:%02d:%02d",minutes,seconds,frames))
end
curves = {}
function PredictBird()
	-- feos, 2014
	-- draws birds trajectories
	-- color marks direction
	for slot = 0, 7 do
		if (memory.readbyte(0x400 + slot) ~= 11) or (memory.readbyte(0x498 + slot) == 0) then
			curves.slot = nil
		else
			if (curves.slot == nil) then curves.slot = {} end
			local ryuY      = memory.readbyte(0x8A)
			local ryuX      = memory.readbyte(0x86)
			local birdY     = memory.readbyte(0x480 + slot)
			local birdX     = memory.readbyte(0x460 + slot)       + memory.readbyte(0x458 + slot)/256
			local birdSpeed = memory.readbytesigned(0x450 + slot) + memory.readbyte(0x448 + slot)/256
			local newY = 0
			local newX = 0
			local newSpeed = 0
			while (#curves.slot <= 200) do
				if (#curves.slot == 0) then
					if (birdY > ryuY)
					then newY = birdY - 1
					else newY = birdY + 1
					end
					if (birdX > ryuX)
					then newSpeed = birdSpeed - 16/256
					else newSpeed = birdSpeed + 16/256
					end
					newX = birdX + newSpeed
				else
					local index = #curves.slot
					local tempY = curves.slot[index].oldY
					local tempX = curves.slot[index].oldX
					local tempSpeed = curves.slot[index].oldSpeed
					if (tempY > ryuY)
					then newY = tempY - 1
					else newY = tempY + 1
					end
					if (tempX > ryuX)
					then newSpeed = tempSpeed - 16/256
					else newSpeed = tempSpeed + 16/256
					end
					newX = tempX + newSpeed
				end				
				table.insert(curves.slot, {oldY = newY, oldX = newX, oldSpeed = newSpeed})
			end
			if (#curves.slot == 200) then table.remove(curves.slot, 1) end			
			for index = 1, #curves.slot do
				local color = nil
				if (curves.slot[index].oldSpeed < 0) then color = "#008800" else color = "#0000ff" end
				gui.box  (curves.slot[index].oldX - 1, curves.slot[index].oldY - 1,
						  curves.slot[index].oldX + 1, curves.slot[index].oldY + 1, color)
			end
			for index = 1, #curves.slot do
				gui.pixel(curves.slot[index].oldX, curves.slot[index].oldY, "white")
			end
		end
	end
end
function GetCell(X,Y)
	local temp = memory.readbyte(0xE7CC+SHIFT(X,4))+memory.readbyte(0x5F)
	if (temp >= 0xC0) then temp = temp-0xC0 end
	Y = Y-0x40
	if (Y < 0) then Y = 0 end
	temp = SHIFT(Y,5)+temp
	return temp
end

function DrawBG(arg,offset,x,y)
	local color2 = "#00ff00ff"
	local function box(color,text)
		gui.box(x,y+offset,x+16,y+offset+16,color)
		if (text == 1) then
			gui.text(x+1,y+offset+1,string.format("%d",arg))
		end
	end
	local function line(up,down,left,right)
		if (up    == 1) then gui.line(x   ,y+offset   ,x+16,y+offset   ,color2) end
		if (down  == 1) then gui.line(x   ,y+offset+16,x+16,y+offset   ,color2) end
		if (left  == 1) then gui.line(x   ,y+offset   ,x   ,y+offset+16,color2) end
		if (right == 1) then gui.line(x+16,y+offset   ,x+16,y+offset+16,color2) end
	end
	if (arg ~= 0) then
		if     (arg == 1) then line(0,0,0,1) -- right wall
		elseif (arg == 2) then line(0,0,1,0) -- left wall
		elseif (arg == 3) then line(0,0,1,1) -- two-sided wall
		elseif (arg == 4) then line(1,0,0,1) -- right corner
		elseif (arg == 5) then line(1,0,1,0) -- left corner
		elseif (arg == 6) then line(1,0,1,1) -- two-sided corner
		elseif (arg == 7) then line(1,0,0,0) -- floor
		elseif (arg == 8) then box("#ff000066",0) -- ejecting block
		elseif (arg == 9) then box("#00ff0066",0) -- ladder
		elseif (arg >= 12) and (arg <= 15)
		then box("#ffffff66",0) -- exits
		else box("#00ff0066",1)
		end
	end
end

function ViewBG(style)
	-- feos, 2014
	-- style: 0=none, 1=new, 2=old, 3=both
	local base = 0x300
	local RyuX = memory.readbyte(0x86)
	local RyuY = memory.readbyte(0x8A)
	local RyuYspeed = memory.readbytesigned(0x89)
	local RyuXspeed = memory.readbytesigned(0xAD)+memory.readbyte(0xAC)/256
	if (AND(memory.readbyte(0x84),4) == 0) then RyuYspeed = 0 end
	local RyuCell = GetCell(RyuX, RyuY+RyuYspeed)
	local RyuRow = math.floor(RyuCell/6)
	local Screen = memory.readwordsigned(0x51)
	if (AND(style,1) == 1)
	and (memory.readbyte(0x1FC) == 0x87)
	or  (memory.readbyte(0x1F3) == 0xD8) then
		for tRow = RyuRow-14, RyuRow+14 do
			for tLine = 0,5 do
				local address = base+((tRow*6+tLine)%0xC0)
				local hi = SHIFT(memory.readbyte(address),  4)
				local lo =   AND(memory.readbyte(address),0xF)
				local x = (tRow-RyuRow)*16+RyuX-RyuX%0x10-Screen%0x10
				local y = tLine*32+64
				DrawBG(hi, 0,x,y)
				DrawBG(lo,16,x,y)
			end
		end
		gui.box(xpos-9,ypos+RyuYspeed-1,xpos+5,ypos+RyuYspeed-5,"#0000ff66")
	end
	if (AND(style,2) == 2) then
		for cell = 0,191 do
			local hi = SHIFT(memory.readbyte(base+cell),  4)
			local lo =   AND(memory.readbyte(base+cell),0xF)
			local bX = math.floor(cell/6)
			local bY = cell%6
			local rX = (RyuRow%32)*6-1
			local rY = math.floor(RyuY/16)*8-32
			if (hi == 0) then hi = " " else hi = string.format("%X",hi) end
			if (lo == 0) then lo = " " else lo = string.format("%X",lo) end
			gui.text(bX*6,bY*16+9,hi.."\n"..lo)
			gui.box(rX,rY,rX+6,rY+8,"#00ff0000")
		end
	end
end
function Spawns()
	-- feos, 2014
	-- uncovers which spawns will occur per frame
	local SubCur= memory.readbyte(0x50)/25.6
	local PosCur= AND(memory.readbyte(0x51),0xF)
	local BlCur = memory.readbyte(0x4E)
	local Blptr = memory.readword(0x96)
	local Yptr  = memory.readword(0x98)
	local IDptr = memory.readword(0x9A)
	local Count = memory.readbyte(0xB4)
	local Iterator = memory.readbyte(0xB5)-8
	local IteratorLast = memory.readbyte(0xB5)-1
	if (Blptr == 0) then return end
	while (Iterator < 0) do Iterator = Count+Iterator end
	if (IteratorLast < 0) then IteratorLast = Count+IteratorLast end	
	local Interrupt = AND(memory.readbyte(0x4C),0x40)
	local forward = memory.readbyte(0x3D)
	if (memory.readbyte(0x1FC) == 0x87)
	or (memory.readbyte(0x1F3) == 0xD8) then
		for i = 0,Count-1 do
			local color1 = "white"
			local block = memory.readbyte(Blptr+i)
			local ypos  = memory.readbyte(Yptr +i)
			local id    = memory.readbyte(IDptr+i)
			local x = i*16%256+1
			local y = 57+math.floor(i/16)*30
			if (block == BlCur) then gui.box(x-1,y-1,x+12,y+23,"#00ff0088") end
			if (forward == 0) then backspawn = -0xD else backspawn = 0xE end
			if (block == (BlCur+backspawn)) then gui.box(x-1,y-1,x+12,y+23,"#ff00ff88") end
			if (i+1 >= Iterator) and (i+1 < Iterator+8)
			or (i+1 < Iterator+8-Count) then color1 = "#ffccaaff" end
			if (Interrupt > 0) then color2 = "red" else color2 = "#44ffffff" end
			gui.text(x,y,string.format("%X\n%X\n%X",block,ypos,id),color1)
			gui.text(108,41,string.format("Block: %X.%02d.%d\nIterator: %02d-%02d/%d",
				BlCur,PosCur,SubCur,Iterator,IteratorLast,Count),color2,"#000000ff")
		end
	end
end

Ninja Gaiden (U) [!].nes.ram.nl

$003D#Whichwayisforward#
$004C#DrawingInterrupt#
$004E#CurrentSpawnBlock#
$0050#temp XposSub#
$0051#temp Xpos#
$0052#temp XposHi#
$005D#NewBlockLo#
$005E#NewBlockHi#
$0060#ScoreLo#
$0061#ScoreHi#
$0062#Timer_frames#
$0063#Timer_seconds#
$0064#ninpo#
$0065#RyuHP#
$0067#ScrollBlockSubS#
$0068#ScrollBlockS#
$0069#ScrollPosSub#
$006A#ScrollPos#
$006B#ScrollBlock#
$006C#ScrollArea#
$006D#Current_stage#
$006E#Current_room#
$0070#ProcLo#
$0071#ProcHi#
$0073#Busy Slots#
$0074#Current Slot#
$0079#temp State#
$007A#temp Facing#
$0084#Ryu state#
$0085#Ryu XposSub#
$0086#Ryu Xpos#
$0087#Ryu YspeedSub#
$0089#Ryu Yspeed#
$008A#Ryu Ypos#
$008C#Ryu BGcollision#
$008E#Ryu BGcollisionX#
$008F#Ryu BGcollisionY#
$0095#Inv. Timer#
$0098#YpointerLo#
$0099#YpointerHi#
$009A#IDpointerLo#
$009B#IDpointerHi#
$0096#BlockPtrLo#
$0097#BlockPtrHi#
$00A2#ScreenPosSub#
$00A3#ScreenPos#
$00AC#Ryu XspeedSub#
$00AD#Ryu Xspeed#
$00B4#SpawnCount#
$00B5#SpawnIterator#
$00BF#Global Timer#
$0300#LevelBlocks#
$0400#ID#
$0408#Timeout#
$0410#Action#
$0438#Movement#
$0440#Facing#
$0448#XspeedSub#
$0450#Xspeed#
$0458#XposSub#
$0460#Xpos#
$0468#YspeedSub#
$0470#Yspeed#
$0478#YposSub#
$0480#Ypos#
$0488#BGcollision#
$0490#HP#
$0498#State#
$0600#Sound#
Ninja Gaiden (U) [!].nes.7.nl

$DD4D#Slot: BusyCheck#
$DD57#Object: Next#
$DD5A#Slot: ScanLoop#
$DD63#Slot: First#
$DD6C#Object: Handle#
$E024#Object: Positioning#
$E243#Object: Common#
$E2E5#Object: Init#
$E66F#Slot: BusyMask#
$F1AC#Object: HandleTemp#
$E677#Collisions: DoAll#
$E67E#Collisions: LowEnough#
$E691#Collisions: UpperRight#
$E6B0#Collisions: LowerRight#
$E6C3#Collisions: UpperLeft#
$E6DD#Collisions: LowerLeft#
$E782#Collisions: Flags#
$E792#Collisions: FindBlockType#
$E7BA#Collisions: CheckBlockHalf#
$E7C0#Collisions: ReadHighNibble#
$E7C7#Collisions: ReadLowNibble#
$EB81#InAir#
$F603#Load New Block#
$F5FB#Six Blocks#
$C195#ProcsLo#
$C196#ProcsHi#
$C21D#Object: Tyson#
$C75D#Object: Bird#
$DFBD#IsRyuAround?#
$C227#Walk (sleep)#
$C29D#Attack!!!#
$C253#Jump (seek)#
$C232#Midair#
$C234#OnGround#
$C264#Aim#
$C276#GetReady#
$DFAB#CheckDistance#
$C259#RyuIsHere!#
$C22D#Act#
$E5D3#ReadPos#
$E5D5#Spawns: GetX#
$E5D9#Spawns: GetSide#
$E5E7#Spawns: GetY#
$E5EE#Spawns: GetID#
$E595#Spawns: CheckNewSpawn#
$E5A6#Spawns: NextUnit#
$E5A7#Spawns: CapTheIterator#
$E144#DmgCollisions#
$E122#CollisionMasks#
$E578#BackSpawn: LeftScroller#
$E581#BackSpawn: RightScroller#
$DDEB#slashing?#
$DDEF#or duckslashing?#
$DECF#SlashCollision#
$DF1F#Damage enemy#
$DF3A#Enemy dead#
$DF3D#Branch if not a boss#
Ninja Gaiden (U) [!].nes.0.nl

$B300#Xhitboxes#
$B400#Yhitboxes#
$B500#Points table#
$B530#HP table#
$B560#Damage table#

Movement

Horizontal Movement

Ryu has only three possible horizontal speeds: 1.5, 1, and 0.5 pixels per frame.
  • 1.5 p/f: when running either direction or pressing forward while airborne.
  • 0.5 p/f: when pressing back while airborne.
  • 1 p/f: when bouncing after taking damage from an enemy, until contact with a wall or platform. (the player has no control over Ryu's movement during this)

Preserving speed

Use of ↔, ← + ↕ or ← or → + B or A (←/→ + B/A only applicable when airborne, and if used for more than one from B and A must alternate every frame) serves to prevent a new speed value from being written, thereby preserving speed when transitioning from one type of movement to another. This is primarily useful for full-speed backwards air movement, but can alsobe used for more precise adjustments to Ryu's position.

Example: ↔ on the frame control is regained after taking damage, then releasing ← and continuing on holding → puts Ryu a half-pixel behind where he'd be if only → had been held, which can actually be favorable in some instances. Care must also be taken to avoid this happening where it would be undesirable, such as pressing ← for one frame mid-jump to trigger an enemy spawn, then pressing →+B on the following frame. This would leave Ryu one pixel behind where he would have been if the attack had come one frame later, after resuming normal forward movement.

Sticky Floors

Landing on certain tiles (mostly found at platform edges, but not always or exclusively) will stop Ryu's forward movement for one frame. Usually this is avoidable, but in cases where it is not, and it is possible to jump on the following frame, it provides an opportunity to execute a special attack without losing time.

Vertical Movement

Ryu move upwards in four ways: jumping from a floor or platform, jumping from a wall, being hit by an enemy, or climbing ladders. Each of these has its own rules, detailed below.
  • standing jump: rises 48 pixels, peaks 19-24 frames after jumping.
  pattern: -4,-4,-4,-4,-4,-3,-3,-3,-3,-3,-2,-2,-2,-2,-1,-1,-1,-1,0,0,0,0,0,0,1...
  • wall jump: rises 15 pixels, peaks 10-14 frames after jumping.
  pattern: -2,-2,-2,-2,-2,-1,-1,-1,-1,-1,0,0,0,0,0,1...
  • damage boost: rises 29 pixels, peaks 14-19 frames after hit.
  pattern: -3,-3,-3,-3,-3,-2,-2,-2,-2,-2,-1,-1,-1,-1,0,0,0,0,0,0,1...
  • climbing a ladder moves Ryu 1 pixel per frame.

Recovery Walljump

When you hit by an enemy, you have no control until Ryu contact with a wall. So the fastest way to reduce 1.0px/f speed and "uncontrollness" length, is jumping into an enemy next to a wall while staying "between" the wall's climbable part and the enemy. This obviously requires enemy position manipulation and Ryu's X and Y positioning.

A perfect Recovery Walljump is possible to carry out with only 1 frame of negative direction (for example a wall-Ryu-enemy situation in 3 frames: →, being hit (-0.5px ~ -1.5px), → + A)

Wall-Climbing

TODO: what do we need to document about this?

Attacking

If you want to know the first frame a given enemy can be hit with the sword from a given jump without many tedious re-records, toggling a cheat that sets $82=2 will keep the sword in the attack state for the rest of a jump after B is pressed. Additionally you can poke some greater value to the enemy's HP to see a range of frames Ryu can attack it. Adjust by one frame for down+B if necessary.

Randomness and manipulation

Knife tossers

From power on, $BF (Global Timer) increments once every frame, from 0 to 255. It is used to determine the delay (in frames) between tosses and the speed of the tossed objects for the four different object-tossing enemies (actually all the same enemy, just with variant sprites). A logical shift right is performed on the value of $BF for the toss-delay (so, 128 possible values). $BF is directly copied to the X and Y sub-pixel speeds and an AND #$01 sets the x speed. The Y speed is simply set to -3.

$BF is also used similarly for the final boss and the 'shrimp' it spews, but with two shift-rights for the spew-timer and a few more steps for the X speed to get possible values between -3 and 3.

Tysons

Tysons constantly do 10-frame jumps, checking if Ryu is around each time they touch the ground. When Ryu is within 32 pixels, they change their action ($410) to "ready" as they land, after the next jump they go "steady", the next jump they attack. It sounds consistent, but in fact it has a lot of randomness.
  • Inherited Y sub-pixels (see below) make them land sooner or later by 1 frame
  • Graphical interrupts (occuring every 10 frames as you run) freeze them for 1 frame.
  • If those interrupts occur right when Tyson is on the ground and is about to change his action, he will fail to do it this time, which means his attack may be delayed by ~10 frames, allowing you to pass.

Birds

Birds look so smart only because their AI is so simple. Each frame they are below Ryu, their Y pos increments, otherwise it decrements. Each frame they are to the right from Ryu, their X speed fractions decrease, otherwise they increase. Use the trajectory script to predict them.

Bats

They spawn at certain Y position which is read from configs, but then gets overwritten. BatSpawnYpos = RyuYpos - 0x10. You would want to manipulate their height if you are going to damage boost from them and land as soon as possible.

Cheetahs

They use to run in one direction all the time, but sometimes they turn around. It happens when they touch the ground and hit the red (sticky) block, first half, that thing that freezes Ryu too if he does it.

Inherited Sub-Pixels (and manipulation)

New enemy sub-pixel position gets added to the subpixel of the previous enemy in this slot that he had while disappearing. If the previous enemy disappeared at 0x07.00, the new one will have position 0xEF.80 (previous 0x08.80 => new 0xF0.00).

There's also a 1 frame window to manipulate this: 1 frame before they would spawn, you remove the direction frame. Obviously this only saves time, if you already need to sacrifice 1.5px.

Spawns, their delays and cancellations

The game divides levels into blocks of ~16 pixels. For each block, level configs are read on which object must spawn. The object limit per room is stored in $B4. $B5 iterates through all possible spawns for a given room, and picks up those whose block matches the current level block. It iterates by 8 units per frame, and the game can spawn up to 30 units per room. The game can't read through all units every frame, if there are more of them than 8, so some spawns get delayed, if the block already requires the spawn, but the iterator isn't at that unit yet.

Objects configs consist of 4 things: target level block, X position, Y position, and ID. X position can only be either 0x10, or 0xF0, putting it on one of the two screen sides. This way, by delaying the spawn of the object relatively to your own progression, you can affect their positions in the level. Screen-wise, it will spawn at the same place, but in the level it will be different. Just track which bunch of units was iterated through this frame, and delay the moment when it matches the current block. Use the Spawns lua function for that.

Another trick is delaying and even cancelling spawns by moving backwards for 1 frame when the iterator runs through the particular spawn unit. If there are many enemies to spawn in the room, it will read that unit only once per 3-4 frames. So during a jump, you can press the opposite direction during these few frames, moving back only by half a pixel, and then again moving forward by 1.5 pixel per frame. But the fewer enemies the room has, the more frames you need to press backward, because iterator would hit the unit in question more often. Sometimes it doesn't even work because of that.

Interrupts

Every ~16 pixels (10-11 frames as you run) occurs and interrupt that loads the new graphics block into video memory. It takes s much time that the frame it occurs most calculations except for Ryu positioning are omitted. If you catch that frame and twitch left-right at 1.5 speed (or just a half pixel, depending on your position), the enemies will freeze. Interrupt is detected by looking at address $4C, which is 0xC1 or 0x80 during those frames.

Level Timer

Every second remaining on the level timer will take three frames to be converted to points and added to the score after a boss is killed—a fact that would seem to be at odds with doing things as fast as possible. But since the timer fractions, the "subtimer", carry over between stage transitions, there will be an optimal range of initial values for the subtimer to have when entering the boss stage so that a second that would otherwise remain on the clock will tick off during the boss fight. A way to find the maximum (the minimum is 0) desired subtimer value for a given, otherwise optimized, boss fight is to compare the 61 frames it takes the subtimer to tick a second off with (F) how many frames it will decrement during the fight (starting at either the first frame of input or the frame after and ending on the frame the boss dies or the frame after). F modulo 61 = max desired subtimer value. With that it can then be determined if the existing subtimer value is optimal or if it will be feasible to manipulate a value within that range.

Glitches with no known application

Taking damage at the same time a boss is killed

TODO: haha, 3-3 actually does this

Vertical screen-wrapping

That happens when taking a hit from a vertical position of 4, 5, 14, 15, 16, 25, 26, 35, 36, 45, 46, 55, 56, 65, 66, 75, 84, 93, 102, or 111 or jumping from a wall with a vertical position of 73, 82, or 91, because there is no cap on falling speed and because the game only checks if Ryu is in the eight pixel death zone at the bottom of the screen, but doesn't care if he passes it, so falling from the right position will just make him wrap around to the top of the screen.

Making Enemies Fall from Platforms

TODO: Spawn position dependent. Anything need to say?

that one thing where you pass through an enemy or grab a power-up and graphics glitch out for a frame

That's a lag frame. The only place where it's not a lag frame is the end of 4-1.

TODO: The block config iterator is not a constant number. 8 for 1-1, 1 for 1-2, 3 for 2-1 etc. It's probably $C1-10 (18 == 8, 13 == 3, 1 == 1 <-- yeah... probably)
TODO: reword prespawn manipulation
TODO: write down enemy slot system ("It's the highest spare slot. Which means if you make it busy yourself, the object will just spawn in the next "highest spare slot".)
TODO: solve the "how to monitor birdy" problem, I think using the speed as a counter MIGHT be enough
TODO: fill in all the gaps


See also



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GameResources/NES/NinjaGaiden last edited by Scumtron on 2016-09-05 16:27:15
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