Editing Source (game engine) (section)

=== Source SDK ===
'''Source SDK''' is the [[software development kit]] for the Source engine, and contains many of the tools used by Valve to develop assets for their games. It comes with several command-line programs designed for special functions within the asset pipeline, as well as a few GUI-based programs designed for handling more complex functions. Source SDK was launched as a free standalone toolset through Steam, and required a Source game to be purchased on the same account. Since the release of ''Left 4 Dead'' in late 2008, Valve began releasing "Authoring Tools" for individual games, which constitute the same programs adapted for each game's engine build. After ''[[Team Fortress 2]]'' became free-to-play, Source SDK was effectively made open to all Steam users. When some Source games were updated to Source 2013, the older Source SDKs were phased out. The three applications mentioned below are now included in the install of each game.{{citation needed|date=October 2021}}

There are three applications packaged in the Source SDK: Hammer Editor, Model Viewer, and Face Poser. The Model Viewer is a program that allows users to view models and can be used for a variety of different purposes, including development. Developers may use the program to view models and their corresponding animations, attachment points, bones, and so on. Face Poser is the tool used to access facial animations and choreography systems.  This tool allows one to edit [[Computer facial animation|facial expressions]], gestures and movements for characters, [[Lip-syncing#In video games|lip sync]] speech, and sequence expressions and other acting cues and preview what the scene will look like in the game engine.<ref>{{cite web |title=Source Engine Licensing - Information Sheet |url=https://valvearchive.com/archive/Half-Life/Half-Life%202/Other/SOURCE_InfoSheet_Q%2101a.FINAL.pdf |publisher=Valve Corporation |access-date=October 12, 2021 |page=6}}</ref>   <!--this isn't the best source, but all the good ones are community wikis-->

==== Hammer Editor ====
{{Redirect|Valve Hammer|the repair tool|Valve hammer}}

The Hammer Editor, the engine's official [[level editor]], uses rendering and compiling tools included in the SDK to create maps using the [[binary space partitioning]] (BSP) method. Level geometry is created with 3D polygons called [[Brush (video games)|brushes]]; each face can be assigned a [[Texture mapping|texture]] which also defines the properties of the surface such as the sounds used for footsteps.<ref>{{cite magazine |title=Building Crown, part two: layout design, textures, and the Hammer editor |url=https://www.pcgamer.com/building-crown-part-two-layout-design-textures-and-the-hammer-editor/ |magazine=[[PC Gamer]] |access-date=September 24, 2021 |language=en |date=March 18, 2014}}</ref> Faces can also be converted into a displacement allowing for more natural shapes such as hills to be created.

Scenery objects or complex geometry can be imported as separate 3D models from the game directory. These models can also be used as physics objects or interactive props. The editor also features an in-depth logic [[Input/output|I/O]] system that can be used to create complex interactive elements. Signals to trigger different responses or change the state of an entity can be sent between entities such as buttons, [[Non-player character|NPCs]], intangible trigger brushes, and map props.