Zero Mission - Charlie Script

-- Charlie uses the following formula for calculating delays:
--     BaseDelay + [808C99C + [3000C77]]
-- BaseDelay = 120 for the first round and when Samus shoots too early
-- BaseDelay = 240 for the second, third, and fourth rounds
-- 3000C77 is a 1 byte frame counter, so its values range from 0-255
-- 808C99C is the location of a table containing the values 0-255 in a random order
-- Therefore, the best delay is 120 or 240, while the worst delay is 375 or 495

-- This script displays three different things:
--   The current timer value is in the top left corner
--   The first column shows what the new timer value will be if Charlie
--     is hit successfully within the first n frames it becomes vulnerable
--   The second column shows what the new timer value will be
--     if Samus hits Charlie too early within the next n frames

-- change this value to see a different number of frames
frameWindow = 18

while true do

    -- display timer
    local timer = memory.readword(0x3000814)
    gui.text(2, 2, timer)

    -- calculate delay if Charlie is successfully hit
    local frame = memory.readbyte(0x3000C77)
    -- calculation is done 3 frames after being hit
    local vulnerable = (timer + frame + 3) % 256
    for i=1,frameWindow do
        local delay = memory.readbyte(0x808C99C + vulnerable)
        color = { delay, 255 - delay, 32 }
        gui.text(18, -6 + i*8, 240 + delay, color)
        vulnerable = (vulnerable + 1) % 256
    end

    -- calculate delay if Samus shoots too early
    for i=1,frameWindow do
        local delay = memory.readbyte(0x808C99C + frame)
        color = { delay, 255 - delay, 32 }
        gui.text(34, -6 + i*8, 120 + delay, color)
        frame = (frame + 1) % 256
    end

    vba.frameadvance()

end