<cat>Dev.Lua</cat> <title>Concepts - Optimization Tips</title> # Knowing When to Optimize Optimization can improve performance, but it can also make code harder to understand and maintain. Correctness and readability should usually come first. Before optimizing, ask: - Is the code complete and working correctly? - Is this code executed frequently enough to matter? - Has profiling identified it as a bottleneck? - Does the improvement justify any loss of readability? - Will other developers need to modify this code later? Saving a few microseconds in code that runs once is rarely worthwhile. The same saving inside `Tick`, `Think`, `HUDPaint`, rendering hooks, or a large loop may be significant because it occurs many times per second. ## Measure Before Optimizing Do not assume that code is slow based only on how it looks. Measure it under realistic conditions. ⤶ <page>SysTime</page> provides sufficiently precise timing for basic benchmarks. Run a benchmark multiple times because LuaJIT compilation, current server load, and calls between Lua and the engine can affect the result. ⤶ <page>Global.SysTime</page> provides sufficiently precise timing for basic benchmarks. Run a benchmark multiple times because LuaJIT compilation, current server load, and calls between Lua and the engine can affect the result. Small benchmarks are useful, but improvements should ultimately be measured in the real system where the code is used. ```lua local iterations = 100000 local startedAt = SysTime() local result = 0 for i = 1, iterations do result = result + i end local elapsed = SysTime() - startedAt -- Using result prevents the benchmarked work from being treated as unused. print( "Result:", result ) print( "Total time:", elapsed ) print( "Average time:", elapsed / iterations ) ``` # The Most Important Tips ## Use Local Variables Lua variables are global unless declared with the `local` keyword. Local variables are scoped to the current scope or function. They prevent accidental conflicts between addons while also being cheaper for the Lua VM to access. Locals are stored in function registers or captured as upvalues. Globals are retrieved from the function's environment, normally _G, using a table lookup. Use a single global addon table when information genuinely needs to be shared between files. ```lua someCounter = 0 -- Global: stored in the current global environment. local someCounter = 0 -- Local: visible only within this scope. -- When files need to share data, expose one addon table rather than many globals. MyAddon = MyAddon or {} MyAddon.RoundState = 0 -- Keep file-internal implementation details local. local internalCounter = 0 ``` ## Avoid Repeated Work and Allocations If a value does not change, calculate or create it once and reuse it. Commonly missed cacheable tables - <page>Color</page>(-s) - <page>Vector</page>(-s) - <page>Angle</page>(-s) - <page>IMaterial</page>(-s) - <page>Entity</page>(-ies) - <page>Player</page>(-s) - <page>Weapon</page>(-s) - Results of expensive searches - Data indexed by a stable identifier Creating temporary tables such as, <page>Color</page>s, <page>Vector</page>s, or <page>Angle</page>s in frequently executed code increases allocation and garbage-collection work. <page>Color</page> and <page>Material</page>s should be cached outside rendering hooks. Do not manually cache the result of <page>player.GetAll</page> merely to iterate over players. Garry's Mod provides <page>player.Iterator</page>, which uses an internal Lua-side cache and avoids creating a new returned table. ```lua -- Unfavorable: creates objects or performs an expensive lookup every frame. hook.Add( "HUDPaint", "OptimizationExample.BadHUD", function() surface.SetMaterial( Material( "icon16/heart.png" ) ) draw.SimpleText( "Healthy", "DermaDefault", 32, 32, Color( 100, 255, 100 ), TEXT_ALIGN_LEFT, TEXT_ALIGN_TOP ) end ) -- Better: create stable objects once and reuse them. local heartMaterial = Material( "icon16/heart.png" ) local healthyColor = Color( 100, 255, 100 ) hook.Add( "HUDPaint", "OptimizationExample.GoodHUD", function() surface.SetMaterial( heartMaterial ) draw.SimpleText( "Healthy", "DermaDefault", 32, 32, healthyColor, TEXT_ALIGN_LEFT, TEXT_ALIGN_TOP ) end ) ``` ```lua -- Unfavorable in a frequently executed hook: -- player.GetAll returns a table for us to iterate. hook.Add( "Tick", "OptimizationExample.BadPlayerIteration", function() local alivePlayers = 0 for _, ply in ipairs( player.GetAll() ) do if ply:Alive() then alivePlayers = alivePlayers + 1 end end DoSomethingWithCount( alivePlayers ) end ) -- Better: -- player.Iterator uses Garry's Mod's internally maintained player cache. hook.Add( "Tick", "OptimizationExample.GoodPlayerIteration", function() local alivePlayers = 0 for _, ply in player.Iterator() do if ply:Alive() then alivePlayers = alivePlayers + 1 end end DoSomethingWithCount( alivePlayers ) end ) ``` ```lua -- This anonymous callback is fine. It is created once when hook.Add runs. hook.Add( "Think", "OptimizationExample.NormalClosure", function() UpdateGameState() end ) -- Unfavorable: creates a table and multiple closures every tick. hook.Add( "Tick", "OptimizationExample.BadTemporaryClosures", function() local actions = {} for _, ply in player.Iterator() do actions[#actions + 1] = function() UpdatePlayer( ply ) end end for i = 1, #actions do actions[i]() end end ) -- Better: perform the work directly when delayed callbacks are unnecessary. hook.Add( "Tick", "OptimizationExample.GoodDirectWork", function() for _, ply in player.Iterator() do UpdatePlayer( ply ) end end ) ``` ## Reuse Mutable Objects Vector arithmetic operators generally return a new Vector. When working with a Vector you own, mutating methods such as <page>Vector:Add</page>, <page>Vector:Mul</page>, and <page>Vector:Set</page> can avoid additional temporary objects. ```lua local basePosition = Vector( 100, 200, 300 ) local labelOffset = Vector( 0, 0, 64 ) -- Creates a copy and then another Vector for the addition result. local positionWithExtraAllocation = Vector( basePosition ) + labelOffset -- Creates one copy, then modifies that copy without another addition result. local positionWithFewerAllocations = Vector( basePosition ) positionWithFewerAllocations:Add( labelOffset ) -- Do not do this unless you intend to permanently change basePosition: -- basePosition:Add( labelOffset ) ``` ## Use Lookup Tables Instead of Searching Covered more in depth on [List-Styled Tables](/gmod/List-Styled_Tables). When a value has a known key, store it under that key. A table lookup is approximately constant-time on average. Searching an array requires checking entries until a match is found and therefore grows linearly with the number of entries. ```lua local actionList = { { Name = "heal", Handler = HealPlayer }, { Name = "armor", Handler = GiveArmor }, { Name = "respawn", Handler = RespawnPlayer } } -- Unfavorable: scans the array until it finds the requested action. local function RunActionBySearching( actionName, ply ) for i = 1, #actionList do local action = actionList[i] if action.Name == actionName then action.Handler( ply ) return true end end return false end -- Better: index handlers by the value used to find them. local actionHandlers = { heal = HealPlayer, armor = GiveArmor, respawn = RespawnPlayer } local function RunActionByLookup( actionName, ply ) local handler = actionHandlers[actionName] if not handler then return false end handler( ply ) return true end ``` ## Localize Frequently Used Functions Repeated table and global lookups can be removed by storing a frequently called function in a local variable. This is most useful when the same stable function is called many times inside a hot path. There is a balance however, Localizing every function makes code harder to read and may provide no meaningful improvement. ```lua local setDrawColor = surface.SetDrawColor local drawRect = surface.DrawRect hook.Add( "HUDPaint", "OptimizationExample.LocalizedFunctions", function() for i = 1, 100 do setDrawColor( 20, 20, 20, 200 ) drawRect( i * 4, 20, 3, 20 ) end end ) -- Avoid localizing every function without evidence that it helps. -- Direct calls are clearer and normally fine: hook.Add( "HUDPaint", "OptimizationExample.DirectFunctions", function() surface.SetDrawColor( 20, 20, 20, 200 ) surface.DrawRect( 20, 50, 200, 20 ) end ) ``` ## Reduce Nested Loops Loops are essential to programming. however two loops over a collection of size n perform approximately n² operations. This is quadratic growth For example: - 3 players compared with every player: 9 comparisons - 20 players compared with every player: 400 comparisons - 100 players compared with every player: 10,000 comparisons Nested loops are not always wrong. Pairwise comparisons genuinely require them in some systems. Before using one, check whether the same work can be done through: - A lookup table - A single pass - Filtering the data first - Spatial partitioning - Processing only changed objects Example: ```lua -- Unfavorable: -- For P players and E entities, this performs approximately P * E iterations. local function UpdateOwnedEntitiesNested() for _, ply in player.Iterator() do for _, ent in ents.Iterator() do if ent:GetOwner() == ply then UpdateOwnedEntity( ply, ent ) end end end end -- Better: -- Visit each entity once and retrieve its owner directly. local function UpdateOwnedEntitiesSinglePass() for _, ent in ents.Iterator() do local owner = ent:GetOwner() if IsValid( owner ) and owner:IsPlayer() then UpdateOwnedEntity( owner, ent ) end end end ``` ## Minimize Networking Network only the information that clients need, and send it only when necessary. Prefer: - Sending changes when they occur instead of every tick - Sending to relevant recipients instead of broadcasting - Sending compact identifiers instead of entire structures - Using exact functions such as net.WriteBool, net.WriteUInt, or net.WriteEntity - Allowing clients to derive values they already have enough information to calculate <page>net.WriteTable</page> adds type and key information for each value. Writing known fields using their exact types is generally smaller and easier to validate. See <page>net.WriteTable</page> and <page>net.WriteUInt</page>. Performance is not the only networking concern. Never trust values received from a client without validating them server-side. Consider reading <page text="Net Library Usage, the Improving part in particular">Net_Library_Usage#improving</page>. ```lua if SERVER then util.AddNetworkString( "OptimizationExample.RoundStateChanged" ) local currentRoundState = 0 local function SetRoundState( newState ) -- Valid values in this example are 0 through 7. newState = math.Clamp( math.floor( newState ), 0, 7 ) -- Do not send an update if nothing changed. if newState == currentRoundState then return end currentRoundState = newState net.Start( "OptimizationExample.RoundStateChanged" ) net.WriteUInt( currentRoundState, 3 ) net.Broadcast() end -- Call SetRoundState only when a game event changes the state. -- Do not call it from Tick merely to resend the current value. end if CLIENT then net.Receive( "OptimizationExample.RoundStateChanged", function() local newRoundState = net.ReadUInt( 3 ) UpdateRoundInterface( newRoundState ) end ) end ``` # Micro-Optimizations Micro-optimizations should come after the larger issues have been addressed. They are most appropriate when: - The system is already correct and complete - Profiling identifies the code as significant - The code runs extremely frequently - The optimized version remains maintainable ### Append Directly to Sequential Arrays Assigning to `#tbl + 1` may be faster than calling <page>table.insert</page> when appending to a dense sequential array. This is only equivalent to appending. Continue using <page>table.insert</page> when inserting at a particular position or when its intent is clearer. ```lua local values = {} local value = 7 -- Clear and readable: table.insert( values, value ) -- Potentially faster for append-only dense arrays: values[#values + 1] = value -- These are not equivalent when inserting at a specific position: table.insert( values, 1, value ) ``` ### Simplify Repeated Mathematics Some mathematically equivalent expressions require fewer operations: - Multiplication by a reciprocal may replace division. - x * x may replace exponentiation by two. - Factoring can remove repeated multiplication. ```lua local x = 10 local y = 20 local z = 30 -- Division by a constant: local halfA = x / 2 local halfB = x * 0.5 -- Squaring: local squaredA = x ^ 2 local squaredB = x * x -- Factoring removes one multiplication: local resultA = x * y + x * z + y * z local resultB = x * ( y + z ) + y * z -- Prefer the clearest version unless profiling demonstrates that the -- alternative provides a meaningful improvement in this exact hot path. ``` # Notable Related Resources - https://gitspartv.github.io/LuaJIT-Benchmarks/ * Focuses on the "Micro-Pico-Optimizations" thing - https://github.com/FPtje/FProfiler * A profiler that will help you find bottlenecks in your code