jump_frz.lua

require "baka-fx.util"

--[[
[Description]
A rotation with a far away \org and a small \frz,
mimicking a straight vertical jump.

[Usage]
jump_frz(base_y, height, dur)
jump_frz(base_y, height, dur, a)
jump_frz(base_y, height, dur, t1, t2)
jump_frz(base_y, height, dur, t1, t2, a)

[Arguments]
base_y: vertical coordinate for the start and end of the jump
height: total height of the jump
dur: total duration of the jump
t1: duration between the start of the syl/line and the start of the jump
t2: duration between the end of the jump and dur
a: acceleration for the vertical movement (works the same as \t's)

[Notes]
A chart is worth a thousand words:

vertical
position
   ^
   |
 base_y
+ height -   x-----x
   |        /       \
 base_y  - x         x
   |       ' '     ' '
   +-------0-t1---t2-dur---> time
--]] 
function jump_frz(base_y, height, dur, ...)
    local radius = 100000
    local rot = height / radius * 180 / math.pi
    local a = 1
    local t1 = dur / 2
    local t2 = dur / 2
    local args = { ... }

    -- Checking arguments
    if #args == 1 then
        a = args[1] > 0 and args[1] or a
    end
    if #args >= 2 then
        t1 = clamp(args[1], 0, dur)
        t2 = clamp(args[2], 0, dur - t1)
    end
    if #args >= 3 then
        a = args[3] > 0 and args[3] or a
    end

    local org = tag("org", -radius, base_y)
    local up = tag("t", 0, t1, a, tag("frz", rot))
    local down = tag("t", dur - t2, dur, 1 / a, tag("frz", 0))

    if t1 == 0 and t2 == 0 then return org .. tag("frz", rot) end
    if t1 == 0 then return org .. tag("frz", rot) .. down end
    if t2 == 0 then return org .. tag("frz", 0) .. up end
    
    return org .. tag("frz", 0) .. up .. down
end