1-- can be overriden by mods
2function core.calculate_knockback(player, hitter, time_from_last_punch, tool_capabilities, dir, distance, damage)
3	if damage == 0 or player:get_armor_groups().immortal then
4		return 0.0
5	end
6
7	local m = 8
8	-- solve m - m*e^(k*4) = 4 for k
9	local k = -0.17328
10	local res = m - m * math.exp(k * damage)
11
12	if distance < 2.0 then
13		res = res * 1.1 -- more knockback when closer
14	elseif distance > 4.0 then
15		res = res * 0.9 -- less when far away
16	end
17	return res
18end
19
20local function vector_absmax(v)
21	local max, abs = math.max, math.abs
22	return max(max(abs(v.x), abs(v.y)), abs(v.z))
23end
24
25core.register_on_punchplayer(function(player, hitter, time_from_last_punch, tool_capabilities, unused_dir, damage)
26	if player:get_hp() == 0 then
27		return -- RIP
28	end
29
30	-- Server::handleCommand_Interact() adds eye offset to one but not the other
31	-- so the direction is slightly off, calculate it ourselves
32	local dir = vector.subtract(player:get_pos(), hitter:get_pos())
33	local d = vector.length(dir)
34	if d ~= 0.0 then
35		dir = vector.divide(dir, d)
36	end
37
38	local k = core.calculate_knockback(player, hitter, time_from_last_punch, tool_capabilities, dir, d, damage)
39
40	local kdir = vector.multiply(dir, k)
41	if vector_absmax(kdir) < 1.0 then
42		return -- barely noticeable, so don't even send
43	end
44
45	player:add_velocity(kdir)
46end)
47