Castlevania II simon's quest collision box viewer (FCEUX)

--Toggles
local show_hud = true
local show_elife = true -- enemy life

-- Player
local px = 0x348
local py = 0x324
local pl = 0x80
local ph = 0x48
local pe = 0x46
local pt = 0x85

-- Enemy
local el = 0x4C2
local ex = 0x348
local ey = 0x324
local oob = 0x3C6
local point = 0x3FC

local function hex(val)
    val = string.format("%X",val)
    return val
end

function findbit(p)
    return 2 ^ (p - 1)
end

function hasbit(x, p)
    return x % (p + p) >= p
end

local function formatstring(adr)
    local str
    if string.len(string.format("%X",memory.readbyte(adr+1))) == 1 then
        str = "0" .. string.format("%X", memory.readbyte(adr+1))
    else
        str = string.format("%X", memory.readbyte(adr+1))
    end
    if adr == pt then
        str = str .. ":"
    end
    if string.len(string.format("%X",memory.readbyte(adr))) == 1 then
        str = str .. "0" .. string.format("%X",memory.readbyte(adr))
    else
        str = str .. string.format("%X", memory.readbyte(adr))
    end
    return str
end

local function buildbox(i)
    local offset1 = memory.readbyte(0x3B4 + i) * 2
    local pointer1 = rom.readbyte(0x4AD0 + offset1) + (rom.readbyte(0x4AD1 + offset1) * 0x100)
    local offset2 = memory.readbyte(0x3FC + i)

    if offset2 > 0 then
        offset2 = offset2 - 1
    end

    local offset3 = rom.readbyte(pointer1 + offset2 - 0x3FF0)
    local offset3 = ((offset3 * 2) + offset3) % 0x100
    local box = { rom.readbytesigned(0x4B8E + offset3), rom.readbyte(0x4B8F + offset3),rom.readbyte(0x4B90 + offset3) } -- yoff/yrad/xrad

    return box
end

local function player()
    local x = memory.readbyte(px)
    local y = memory.readbyte(py)

    gui.box(x - 6,y + 3 - 0x0A,x + 6,y + 3 + 0x0A,"#0000FF40","#0000FFFF")

    -- Whip
    if memory.readbyte(0x445) == 3 then
        local wxoff = 0x16
        local wyoff = -4
        local wxrad
        local wyrad = 4
        local woff = memory.readbyte(0x434)
        if memory.readbyte(0x420) == 0 then
            wxoff = wxoff * -1
        end
        wxrad = rom.readbyte(0x4BED + woff)
        gui.box(x+wxoff-wxrad,y+wyoff-wyrad,x+wxoff+wxrad,y+wyoff+wyrad,"#FFFFFF40","#FFFFFFFF")

    end
end

local function objects()
    local x
    local y
    local l
    local box
    local active
    local fill
    local outl
    local isoob
    local etype
    for i = 2,19,1 do
        active = memory.readbyte(0x3D8 + i)
        isoob = memory.readbyte(oob + i)
        etype = memory.readbyte(0x3B4 +i)
        if etype > 0 and etype ~= 0x43 and etype ~= 0x1E and etype ~= 0x2A then
            box = buildbox(i)
            x = memory.readbyte(ex + i)
            y = memory.readbyte(ey + i)
            l = memory.readbyte(el + i)
            if hasbit(active,findbit(1)) and not hasbit(active,findbit(8)) then  -- Enemy

                if bit.rshift(bit.band(isoob,0xF0),4) ~= 8 and bit.rshift(bit.band(isoob,0xF0),4) ~= 4 then  -- If not offscreen
                    if show_elife == true then
                        gui.text(x-8,y-28,"HP: " .. l)
                    end
                end
                fill = "#FF000040"
                outl = "#FF0000FF"
            elseif hasbit(active,findbit(8)) and hasbit(active,findbit(1)) then -- Hidden enemy, no active box
                outl = "#FF000040"
                fill = "#FF000000"

                if bit.rshift(bit.band(isoob,0xF0),4) ~= 8 and bit.rshift(bit.band(isoob,0xF0),4) ~= 4 then  -- If not offscreen
                    if show_elife == true then
                        gui.text(x-8,y-28,"HP: " .. l)
                    end
                end
            elseif hasbit(active,findbit(8)) and hasbit(active,findbit(2)) then  -- Simon's projectiles
                outl = "#00FFFFFF"
                fill = "#00FFFF40"
            elseif not hasbit(active,findbit(8)) and hasbit(active,(2)) then -- Enemy projectile
                outl = "#FFFF00FF"
                fill = "#FFFF0040"
            elseif hasbit(active,findbit(8)) and not hasbit(active,findbit(2)) then  -- Inactive box
                outl = 0
                fill = 0
            elseif hasbit(active,findbit(7)) then -- NPC
                outl = "#FF00FFFF"
                fill = "#FF00FF40"
            elseif hasbit(active,findbit(3)) then -- Item pickups
                outl = "#FFA500FF"
                fill = "#FFA50040"
            end
            if bit.rshift(bit.band(isoob,0xF0),4) ~= 8 and bit.rshift(bit.band(isoob,0xF0),4) ~= 4 then  -- If not offscreen
                gui.box(x - box[3],y+box[1]+box[2],x+box[3],y+box[1]-box[2],fill,outl)
            end

        end

    end

end


local function HUD()
    local l = memory.readbyte(pl)
    local h = 0
    local e = 0
    local t = 0

    -- Hearts
    h = formatstring(ph)
    -- Experience
    e = formatstring(pe)
    -- Time
    t = formatstring(pt)

    gui.text(14, 9, l)
    gui.text(256 - 40, 09,"H: " .. h)
    gui.text(256 - 40, 17,"E: " .. e)
    gui.text(256 - 85, 09, "T: " .. t)
end

emu.registerafter(function()
    if show_hud == true then
        HUD()
    end
    player()
    objects()
    -- emu.frameadvance()
end)