Enchanting Trees

Without further delay. Lets get to it!
npc_abilities_custom.txt entry for our ability.

"enchant_tree_lua"

{

// These are required for this to work

"BaseClass" "ability_lua"

"ScriptFile" "lua_abilities/enchant_tree/ability.lua" //set your script file path in 'vscripts' folder

"AbilityBehavior" "DOTA_ABILITY_BEHAVIOR_UNIT_TARGET"

"AbilityUnitTargetTeam" "DOTA_UNIT_TARGET_TEAM_CUSTOM"

"AbilityUnitTargetType" "DOTA_UNIT_TARGET_TREE"

"AbilityDuration" "10.0" //well, technically optional.

// Optional stuff

"AbilityTextureName" "enchant_tree_lua"

"AbilityCastPoint" "0.1"

"AbilityCooldown" "5.0"

"AbilityManaCost" "100"

"AbilityCastRange" "400"

}

This is your basic start for lua ability.

if enchant_tree_lua == nil then

enchant_tree_lua = class({})

end

LinkLuaModifier( "enchant_tree_lua_mod", "lua_abilities/enchant_tree/modifier.lua", LUA_MODIFIER_MOTION_NONE )

The magic happens here. CreateModifierThinker creates sort of invisible unit with modifier attached to it.

function enchant_tree_lua:OnSpellStart()

CreateModifierThinker( self:GetCaster(), self, "enchant_tree_lua_mod", { duration = self:GetDuration() }, self:GetCursorPosition(), self:GetCaster():GetTeamNumber(), true )

end

Now for the next piece of magic we need to setup our cool modifier. In this example the file path would be "vscripts/lua_abilities/enchant_tree/modifier.lua".
There are two major parts for every 'tree enchantment'. First is making sure that we have tree nearby. Because of engine limitations the trees are difficult to interact with. For our solution we are simply requesting from gridnav every half a second if there is trees in very small area at our thinker unit's location.
The last part is minor optimization that may become redundant but was not at the time of developing this. There was issue where the thinker unit would remain on the map for some time after the modifier was destroyed.

if enchant_tree_lua_mod == nil then

enchant_tree_lua_mod = class({})

end

function enchant_tree_lua_mod:OnCreated( kv )

if IsServer() then

self:StartIntervalThink(0.5)

end

end

function enchant_tree_lua_mod:OnIntervalThink()

if IsServer() then

if not GridNav:IsNearbyTree(self:GetParent():GetAbsOrigin(), 10, false) then

self:Destroy()

end

end

end

function enchant_tree_lua_mod:OnDestroy()

if IsServer() then

UTIL_Remove( self:GetParent() )

end

end

Now comes the fun part. What do we want to do with this modifier.
I decided to go with soul collecting tree: if enemy hero is killed in radius(you need to add this to special values of your npc_abilities_custom.txt) the owner of the spell steal up to 2 of victim's primary stat.

function enchant_tree_lua_mod:DeclareFunctions()

local funcs = {

MODIFIER_EVENT_ON_HERO_KILLED

}

return funcs

end

function enchant_tree_lua_mod:OnHeroKilled(kv)

if IsServer() then

if kv.unit and kv.unit:GetTeam() ~= self:GetCaster():GetTeam() then

if (self:GetParent():GetAbsOrigin() - kv.unit:GetAbsOrigin()):Length2D() <= self:GetAbility():GetSpecialValueFor("radius") then

self:CollectSoul(kv.unit)

end

end

end

end

function enchant_tree_lua_mod:CollectSoul(hTarget)

local primary = hTarget:GetPrimaryAttribute()

local val = hTarget:GetPrimaryStatValue()

local n = math.max (0, math.min(2,val))

if primary == 0 then

self:GetCaster():ModifyStrength(n)

hTarget:ModifyStrength(n*-1)

elseif primary == 1 then

self:GetCaster():ModifyAgility(n)

hTarget:ModifyAgility(n*-1)

else

self:GetCaster():ModifyIntellect(n)

hTarget:ModifyIntellect(n*-1)

end

end

For those fancy effects that ironwood tree has you might want to add these lines

function enchant_tree_lua_mod:GetEffectName()

return "particles/items_fx/ironwood_tree.vpcf"

end

function enchant_tree_lua_mod:GetEffectAttachType()

return PATTACH_OVERHEAD_FOLLOW

end

Next Topic: Stacking Modifiers