Contrary to popular belief, the docs in the MUGEN folder are very helpful. It breaks it down step by step so you understand what each part of the sctrl is for. Here is what it says about AfterImage:
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AfterImage
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Enables player afterimage effects. The character's frames are stored in a history buffer, and are displayed after a delay as afterimages.
Required parameters:
none
Optional parameters:
time = duration (int)
Specifies the number of ticks that the afterimages should be
displayed for. Set to -1 to display indefinitely. Defaults to 1.
length = no_of_frames (int)
Sets the capacity of the frame history buffer. The history will
hold up to no_of_frames of the character's most recently saved
frames. Assuming constant values for timegap and framegap,
increasing the length can increase the number and "age" (for lack
of a better term) of afterimages displayed at one time. The
maximum length is 60, and the default is 20.
palcolor = col (int)
palinvertall = invertall (bool)
palbright = add_r, add_g, add_b (int)
palcontrast = mul_r,mul_g, mul_b (int)
palpostbright = add2_r,add2_g, add2_b (int)
These parameters determine palette effects to be applied to all afterimages. First the color level is adjusted according to the palcolor value, then if invertall is non-zero the colors are inverted. Afterwards, the palbright components are added to the corresponding component of the player's palette, then each component is multiplied by the corresponding palcontrast component divided by 256, then the palpostbright components are added to the result. The value of palcolor ranges from 0 (greyscale) to 256 (normal color). For instance, if the red component of the character's palette is denoted pal_r, then the red component of the afterimage palette is given by (pal_r+add_r)*mul_r/256 + add2_r, assuming palcolor and palinvert are left at their default values. Valid values are 0-256 for palcolor, 0-255 for palbright and palpostbright components, and any non-negative integer for palcontrast components. The defaults are:
palcolor = 256
palinvertall = 0
palbright = 30,30,30
palcontrast = 120,120,220
palpostbright = 0,0,0
paladd = add_r, add_g, add_b (int)
palmul = mul_r,mul_g, mul_b (float)
These parameters specify palette effects that are applied repeatedly to successive frames in the afterimage. In one application of these palette effects, first the paladd components are added to the afterimage palette, then the components are multiplied by the palmul multipliers. These effects are applied zero times to the most recent afterimage frame, once to the second-newest afterimage frame, twice in succession to the third-newest afterimage frame, etc. Valid values are 0-255 for the paladd components, and any non-negative float value for the palmul multipliers. The defaults are:
paladd = 10,10,25
palmul = .65,.65,.75
timegap = value (int)
This parameter controls how many frames to skip between saving
player frames to the history buffer for afterimage display. The
default is 1 (skip no frames). To save every third frame (for
example), you would use timegap = 3.
framegap = value (int)
Every value'th frame in the history buffer will be displayed as an
afterimage. For instance, if framegap = 4 (the default), then the
first, fifth, ninth, ... frames of the history buffer will be
displayed as afterimages.
trans = type (string)
Specifies the transparency type for the afterimages. Valid types
are "none" for an opaque afterimage, "add", "add1", and "sub".
Example:
(This is my own example. This is what I am using for Iceman's "thrust" kick which shows an After Image of Iceman for a short period of time. Play with the settings to see if you get the desired results)
[State 225, Afterimage]
type = AfterImage
trigger1 = Time = 0
length = 13
PalBright = 30, 30, 0
PalContrast = 70, 70, 20
PalAdd = -10,-10,-10
PalMul = .85,.85,.50
TimeGap = 1
FrameGap = 2
Trans = Add
time = 2
April Fools