TNT: Add explode_center flag

Add 'explode_centre' flag which when false explodes as normal and when true runs on_blast on centre node as well as dropping items.

game_api.txt

@@ -363,7 +363,8 @@ TNT API
^ Create an explosion.

* `position` The center of explosion.
* `definition` The TNT definion as passed to `tnt.register`
* `definition` The TNT definion as passed to `tnt.register` with the following addition:
 * `explode_center` false by default which removes TNT node on blast, when true will explode center node.

`tnt.burn(position, [nodename])`

mods/tnt/init.lua

@@ -208,6 +208,7 @@ local function add_effects(pos, radius, drops)
		collisiondetection = false,
		vertical = false,
		texture = "tnt_boom.png",
		glow = 15,
	})
	minetest.add_particlespawner({
		amount = 64,
@@ -272,7 +273,7 @@ function tnt.burn(pos, nodename)
	end
end

local function tnt_explode(pos, radius, ignore_protection, ignore_on_blast, owner)
local function tnt_explode(pos, radius, ignore_protection, ignore_on_blast, owner, explode_center)
	pos = vector.round(pos)
	-- scan for adjacent TNT nodes first, and enlarge the explosion
	local vm1 = VoxelManip()
@@ -286,6 +287,10 @@ local function tnt_explode(pos, radius, ignore_protection, ignore_on_blast, owne
	local c_tnt_burning = minetest.get_content_id("tnt:tnt_burning")
	local c_tnt_boom = minetest.get_content_id("tnt:boom")
	local c_air = minetest.get_content_id("air")
	-- make sure we still have explosion even when centre node isnt tnt related
	if explode_center then
		count = 1
	end

	for z = pos.z - 2, pos.z + 2 do
	for y = pos.y - 2, pos.y + 2 do
@@ -384,12 +389,14 @@ end
function tnt.boom(pos, def)
	local meta = minetest.get_meta(pos)
	local owner = meta:get_string("owner")
	if not def.explode_center then
		minetest.set_node(pos, {name = "tnt:boom"})
	end
	local sound = def.sound or "tnt_explode"
	minetest.sound_play(sound, {pos = pos, gain = 1.5,
			max_hear_distance = math.min(def.radius * 20, 128)})
	minetest.set_node(pos, {name = "tnt:boom"})
	local drops, radius = tnt_explode(pos, def.radius, def.ignore_protection,
			def.ignore_on_blast, owner)
			def.ignore_on_blast, owner, def.explode_center)
	-- append entity drops
	local damage_radius = (radius / def.radius) * def.damage_radius
	entity_physics(pos, damage_radius, drops)