Box modeling

Box modeling means starting from a simple primitive, usually a cube or cylinder, and refining it step by step with extrudes, insets and loop cuts. You work from big shapes to small ones, so the proportions are right before you spend time on detail.

It is the method most people learn first, and it is still how many game props are built. It also pairs naturally with subdivision: you edit a light, blocky cage and let the computer show the smooth result.

#Why start from a box

Starting from a primitive keeps you thinking about volume and silhouette first. Experienced artists on Polycount describe the same order of work: block out without worrying about final topology, then clean up. FrankPolygon adds that "starting with clean, well organized topology on a base mesh will make additional modeling operations easier" (Polycount: Need opinion on what a good topology is).

A box is also already made of quads, and every operation below keeps it that way if you use them carefully. That matters because quads form continuous edge loops, which you need for loop cuts, loop selection and predictable subdivision (Blender Manual: Structure).

#The core operations

Box modeling uses a small toolkit. The names differ between programs, but the ideas are the same.

• Extrude: pull a face or edge out, creating new side faces. This is how a box grows arms, handles or legs.
• Inset: create a smaller face inside a face, joined by a ring of quads. Insets are how you start panels, recesses and buttons.
• Loop cut: add a new edge loop across an edge ring. Loop cuts add resolution exactly where you need it.
• Bevel: split an edge into several, rounding or chamfering it. See bevels and chamfers.
• Loop and ring selection: select whole loops or rings in one click so you can scale, slide or bevel them. In Blender, Alt-click selects an edge loop and Ctrl-Alt-click selects an edge ring (Blender Manual: Select Loops).

You will spend most of your time with these five. Booleans, deforms and sculpting tools can join later.

#A typical sequence

1. Block the main volume. Scale a cube to the object's bounding box at real-world scale.
2. Add major divisions. Loop-cut where the big shapes change: the lid of a crate, the neck of a bottle.
3. Extrude secondary forms. Handles, feet, spouts.
4. Inset and extrude details. Panels, recesses, rims.
5. Control the edges. Decide which corners are sharp and which are soft, using support loops, creases or bevels.
6. Check the smooth result. Turn subdivision on and look for pinching, wobbles and stretched faces.

The Blender Manual notes that a mesh with deliberate topology "has good placement of edge loops", which lets you add more loops where you want sharper edges and remove them where you want softer ones (Blender Manual: Subdivision Surface Modifier). This is the basis of step 5.

#Box modeling and subdivision

Box modeling is often used to build a subdivision cage. The cage stays light, but the subdivided surface is smooth.

Pixar's OpenSubdiv documentation describes the cage as what "is manipulated by a designer" while the smooth surface follows it (OpenSubdiv documentation: Subdivision Surfaces). It also warns that an arbitrary mesh "will often not make a good subdivision cage, regardless of how good that polygonal mesh appears" (OpenSubdiv documentation: Subdivision Surfaces). So a box-modeled cage needs more care than a mesh you will never subdivide:

• Keep it all quads where possible. Triangles "can pose problems when animating or subdividing" (BlenderWiki: Mesh topology appendix).
• Keep poles (vertices with three, five or more edges) away from curved, highly visible areas.
• Add support loops to control how tightly edges round off.

If the mesh will not be subdivided, these rules relax a lot. A low-poly game prop can use triangles and n-gons freely, as long as it is triangulated consistently before baking (Polycount: Need opinion on what a good topology is; Marmoset: The Toolbag Baking Tutorial).

#Worked examples

#Common mistakes

• Adding loops everywhere. Loop cuts run all the way around the mesh, so one careless cut can add resolution where you do not need it. Plan cuts, or end loops with a pole in a flat area.
• Ignoring scale. A box-modeled prop made at the wrong size will cause texel density and lighting problems later. Check units, scale and axes.
• Forgetting the low-poly. If the model is a high-poly for baking, plan which loops the low-poly will keep. See the high-to-low workflow.
• Triangles in a subdivision cage. Each one can create a small wobble or pinch. On a mesh you will never subdivide, they are fine.

#In different tools

• Blender: Alt-click and Ctrl-Alt-click select loops and rings, and a loop stops when it reaches a pole (Blender Manual: Select Loops). The Subdivision Surface modifier previews the smooth result non-destructively and uses OpenSubdiv as its backend (Blender Manual: Subdivision Surface Modifier).
• Maya and 3ds Max: both have equivalent extrude, inset, bevel and loop tools, plus smooth-mesh previews. The workflow on this page carries over directly.

#Further reading and watching