Greebles

Greebles are "small relief details used to give visual complexity to a model" (Wikipedia: Greeble): panels, pipes, vents, boxes and ribs added to a larger form. Adding them is called greebling. On a spaceship hull, a sci-fi corridor wall or a mech, greebles make a simple shape read as a complex, working machine.

#Where the word comes from

The term goes back to the model shop. Wikipedia credits George Lucas with coining "greeblies" in the 1970s "to describe details on model ships used in the production of Star Wars" (Wikipedia: Greeble). 99% Invisible explains the method: many of the ships "started out as relatively bland models" and were then covered in "ready-made pieces from store-bought toy model kits" (99% Invisible: Interstellar Illusions: 'Greebles' Lend Large…). That is kitbashing in its original, physical form.

Other names exist. Ron Thornton is credited with "nurnies" for the CGI detail his company Foundation Imaging made for Babylon 5, and the 2001: A Space Odyssey model makers reportedly called them "wiggets" (Wikipedia: Greeble).

#How greebles suggest scale

Greebles are, in 99% Invisible's words, "a trick to imply scale through complexity" (99% Invisible: Interstellar Illusions: 'Greebles' Lend Large…). "As humans, we use details as cues to estimate size", especially when there is nothing else to compare against (99% Invisible: Interstellar Illusions: 'Greebles' Lend Large…). A plain grey box could be any size; the same box covered in tiny vents and hatches reads as huge. Greebles also imply mechanical function "without necessarily having any real purpose" (Wikipedia: Greeble): the viewer assumes the pipes go somewhere.

This links greebles to scale and proportion and primary, secondary and tertiary forms. Greebles are tertiary detail: they only work on top of strong primary and secondary shapes.

#Building greebles for games

Greebles cost triangles, and in a game they repeat across large surfaces. Artists therefore build them in different ways depending on distance and budget. Each method has its own page:

• Modeled into the mesh, for silhouette-breaking detail the player sees up close. See hard-surface modeling and booleans.
• Baked into a normal map from a high poly, often as floaters that hover above the surface during the bake. See the high-to-low workflow.
• Kit pieces and kitbash libraries placed by hand: reusable vents, pipes and panels. See kitbashing.
• Mesh decals and trim sheets, which add panel lines and small parts on cheap geometry. See mesh decals and trim sheets.
• Procedural scattering, where a tool distributes detail over a surface by rules. See procedural modeling.

A common split: modeled greebles where they change the silhouette, baked or decal greebles where they only change the surface.

#Greebles in shipped games

In games, greebling is mostly done with shared libraries rather than one-off parts. On DOOM Eternal, environment artist Chase Long describes "springboarding and KitBashing off of each other's work", going through "the growing library of environmental assets", and says kitbashing helped "keep visual continuity, save time" (80 Level: Designing Environments for DOOM Eternal). A shared set of mechanical parts keeps the rooms visually consistent.

Star Citizen's Grim Hex is a pirate outpost inside a hollowed-out asteroid, deliberately rundown and cobbled together. Tom Radford's breakdown of its hangars says he reworked and kitbashed existing Grim Hex assets into larger, more optimised meshes (ArtStation: Star Citizen: Grim Hex - Hangars): greeble-heavy sci-fi detail, merged so it costs less to draw. Commercial libraries such as KitBash3D sell the same idea as themed kits for "environment artists" and others (ArtStation Magazine: Don't Wait to Create with KitBash3d).

#Related terms

kitbashing · floaters · mesh decals · hard-surface modeling · primary, secondary and tertiary forms · scale and proportion

#Further reading and watching