MTASA has some interesting caveats with NPC damage synchronization and processLineOfSight function

caveats.lua

SERVER_SIDE = guiGetScreenSize == nil
CLIENT_SIDE = guiGetScreenSize ~= nil


---------------
-- LIFECYCLE --
---------------

if SERVER_SIDE then
    addEventHandler('onResourceStart', resourceRoot, function()
        SERVER_PED_A = Ped(17, -1316, -59,15)
        SERVER_PED_C = Ped(19, -1320, -59,15)
        
        SERVER_PED_C:setRotation(0,0,270)
        SERVER_PED_C:giveWeapon(25, 9999, true)
    end)

    addEvent('syncPed', true)
    addEventHandler('syncPed', resourceRoot, function()
        triggerClientEvent(root, 'syncPed', resourceRoot, SERVER_PED_A, SERVER_PED_C)

        SYNCER_HOST = getPlayerFromName('toliak')
        SYNCER_HELPER = getPlayerFromName('toliak_helper')

        if SERVER_PED_A:getSyncer() ~= SYNCER_HOST then
            SERVER_PED_A:setSyncer(SYNCER_HOST)
        end
        -- 
        if SERVER_PED_C:getSyncer() ~= SYNCER_HELPER then
            SERVER_PED_C:setSyncer(SYNCER_HELPER)
        end
    end)
end

if CLIENT_SIDE then
    addEventHandler('onClientResourceStart', resourceRoot, function()
        triggerServerEvent('syncPed', resourceRoot)
    end)

    addEvent('syncPed', true)
    addEventHandler('syncPed', resourceRoot, function(b,c)
        CLIENT_PED_A = b
        CLIENT_PED_C = c

        local marker = Marker(0,0,0,'arrow',.5,0,255,0,200)
        marker:attach(CLIENT_PED_A, 0, 0, 1.6)
    end)
end


-------------------
-- LINE OF SIGHT --
-------------------

if CLIENT_SIDE then 
    LOS_POSITION = {}
    for i=1,10 do  --100 
        for j=1,5 do --50
            table.insert(LOS_POSITION, {
                Vector3(-1331 + i/10, 23 - j*1.01,14.3),
                Vector3(-1331 + i/10, 22 - j*1.01,14.3)
            })
        end
    end
    lineOfSightElement = nil

    addEventHandler('onClientPreRender', root, function()
        if localPlayer.name ~= 'toliak' then 
            return
        end
        
        local hitElemenAccum = nil
        for _,v in ipairs(LOS_POSITION) do
            -- or isLineOfSightClear
            local hit, x,y,z, hitElement = isLineOfSightClear(
                v[1], 
                v[2])
            -- `not hit`, if `isLineOfSightClear` selected
            hitElemenAccum = hitElemenAccum or not hit
        end
        lineOfSightElement = hitElemenAccum
    end)

    addEventHandler('onClientRender', root, function()
        for _,v in ipairs(LOS_POSITION) do
            dxDrawLine3D(v[1], v[2])
        end
    end)
end

---------------
-- STATISTIC --
---------------

if CLIENT_SIDE then
    SCREEN_W, SCREEN_H = guiGetScreenSize()

    addEventHandler('onClientPedDamage', root, function()
        if source ~= CLIENT_PED_A then
            return
        end

        outputChatBox(tostring(getRealTime().timestamp) .. ' damaged (client) ')
    end)


    addEventHandler('onClientRender', root, function()
        if localPlayer.name ~= 'toliak' then 
            return
        end

        if not CLIENT_PED_A then
            return
        end

        local syncerText = 'Not syncer'
        if CLIENT_PED_A:isSyncer() then
            syncerText = 'Syncer'
        end

        local streamedInText = 'Not streamed in'
        if CLIENT_PED_A:isStreamedIn() then
            streamedInText = 'Streamed in'
        end

        local streamableText = 'Always streamable'
        if CLIENT_PED_A:isStreamable() then
            streamableText = 'Streamable'
        end

        local position = ('%d %d %d'):format(
            CLIENT_PED_A.position.x,
            CLIENT_PED_A.position.y,
            CLIENT_PED_A.position.z
        )

        dxDrawText(
            tostring(math.floor(CLIENT_PED_A.health)) 
                .. '\n' .. syncerText 
                .. '\n'.. streamedInText 
                .. '\n' .. streamableText 
                .. '\n' .. position
                .. '\n', 
            SCREEN_W - 600, 
            SCREEN_H - 500, 
            SCREEN_W,
            SCREEN_H,
            0xFFFFFFFF, 
            3.5
        )
    end)
end


-----------
-- BINDS --
-----------

if CLIENT_SIDE then
    bindKey('num_2', 'down', function()
        CLIENT_PED_C:setAimTarget(CLIENT_PED_A.position)
        CLIENT_PED_C:setControlState('aim_weapon', true)
    end)

    bindKey('num_3', 'down', function()
        CLIENT_PED_C:setControlState('fire', true)
    end)

    bindKey('num_3', 'up', function()
        CLIENT_PED_C:setControlState('fire', false)
    end)
end