Animation System

Overview

The animation system in IKEMEN Go / MUGEN connects sprites to gameplay through .air (Animation) files. Each animation is an "Action" consisting of frames that display sprites with timing, position offsets, and collision boxes.

.air File Format

Action Header

[Begin Action 0]    ; Action number (matches anim= in Statedef or ChangeAnim)

Frame Format

Each line after the header defines one frame:

Group, Image, OffsetX, OffsetY, DisplayTime[, Flip][, Color]

• •Group: Sprite group number in .sff (e.g., 0 for idle sprites)
• •Image: Sprite image index within group (e.g., 0, 1, 2...)
• •OffsetX: Horizontal offset from character axis (positive = forward)
• •OffsetY: Vertical offset from character axis (negative = up from ground)
• •DisplayTime: Ticks to display this frame
  • •Positive: display for N ticks
  • •-1: Hold indefinitely (last frame of non-looping animation)
  • •0: Display for 0 ticks (skip frame, used for collision-only frames)
• •Flip: Optional. H = horizontal flip, V = vertical flip, VH = both
• •Color: Optional. Blend mode: A = add, A1 = add1, S = subtract, AS???D??? = custom alpha

Special Directives

Loopstart: Marks where looping animations restart from

[Begin Action 0]  ; Idle - loops forever
0,0, 0,0, 7
0,1, 0,0, 7
Loopstart          ; Loop restarts from next frame
0,2, 0,0, 7
0,3, 0,0, 7
0,4, 0,0, 7

Interpolation (IKEMEN Go only):

[Begin Action 100]
Interpolate Offset  ; Smooth position transitions between frames
Interpolate Angle   ; Smooth angle transitions
Interpolate Scale   ; Smooth scale transitions
Interpolate Blend   ; Smooth blend transitions
100,0, 0,0, 5
100,1, 10,0, 5     ; Position smoothly interpolates from (0,0) to (10,0)

Collision Boxes (Clsn)

Collision boxes define where a character can be hit and where attacks connect.

Clsn Types

• •Clsn1: Attack box (hitbox) -- where your attack hits
• •Clsn2: Vulnerable box (hurtbox) -- where you can be hit

Clsn Syntax

; Per-frame collision boxes
Clsn1: 1                    ; 1 attack box for next frame only
Clsn1[0] = x1, y1, x2, y2  ; Left, Top, Right, Bottom

Clsn2: 2                    ; 2 hurt boxes for next frame only
Clsn2[0] = -15, -90, 15, 0  ; Body hurtbox
Clsn2[1] = -10, -100, 10, -90 ; Head hurtbox

Clsn Defaults (apply to all subsequent frames until overridden)

Clsn2Default: 2             ; Default hurtboxes for ALL frames in this action
Clsn2[0] = -15, -80, 15, 0
Clsn2[1] = -10, -95, 10, -80

Coordinate System for Boxes

• •Origin (0,0) = character's axis point (feet center)
• •X: negative = behind character, positive = in front
• •Y: negative = above ground, positive = below ground (rarely used)
• •Box: x1,y1 = top-left corner, x2,y2 = bottom-right corner
• •Example: -15, -90, 15, 0 = box from 15 pixels behind to 15 front, ground to 90 up

Standard Sprite Groups

Animation Timing Guide

For a 60fps engine:

• •1 tick = 1/60th of a second (approx 16.67ms)
• •7 ticks (approx 0.117s) = common idle frame time
• •3 ticks = startup frame (fast attack)
• •4-5 ticks = active frame
• •6-8 ticks = recovery frame

Frame Data Convention

• •Startup: Frames before the hitbox appears
• •Active: Frames where the hitbox exists (Clsn1 present)
• •Recovery: Frames after hitbox disappears until control returns
• •Example: Light punch = 3 startup + 3 active + 6 recovery = 12 frames total

Tips

1. •Always set Clsn2Default for hurtboxes that stay consistent
2. •Only add Clsn1 (hitbox) on active attack frames
3. •Use Loopstart for idle, walk, and run animations
4. •Use -1 display time for the last frame of attack animations (held until state changes)
5. •Keep sprite offsets at 0,0 unless the character needs to shift position during animation
6. •Match animation action numbers to statedef numbers (Action 200 = State 200) for clarity
7. •IKEMEN Go interpolation directives can smooth movement without extra sprites
8. •Test collision boxes in debug mode (Ctrl+C in IKEMEN Go) to visualize them in-game