Help, I’m reading through the following Blender documentation and get totally lost on the very first page of the section about “extrude” (in Chapter 6): I’ve understood everything else up to chapter 6, including the definitions of vertices, edges, and 3- and 4-point faces:
When I tried to do the “gus” gingerbread man extrusion example in the documentation, he came out pretty messed up looking, and I’m sure it’s because I don’t understand this section. When I finished with Gus, he looked ok from a distance, but in a zoom-in, had strange places where he seemed to “turn inside out”, parts that were “twisted”, multiple faces where there should’ve just been one, strange “folds” in his body, arms and legs that weren’t closed off properly that you could “look up inside of”, etc.
QUESTIONS ON EXTRUDE FUNCTION IN GENERAL
First can someone tell me if I even understand what “extrude” means?:
Webster’s defines “extrude” as, in the field of metals & plastics: To shape or form an object by forcing it through a die. I get a visual of the old Play-Dough toys where you put a flat plastic “die” with a cut-out shape of a circle, square, or star, turn the crank, and it forces the dough through that cutout hole into a 3-d object with that cross-sectional shape.
So, I’d assume the purpose of the Extrude function in Blender is to allow you to take any arbitrary-shaped 2-dimensional object (circle, square, star), and “push the dough through” to make a 3-d version which can be along a straight or curved path. I.e., a circle gets “extruded” into a cylinder or a curved garden hose.
So I’d assume there’s 2 things needed: One set of edges that describes an enclosed 2-D shape, and one path (curved or straight) going out (perpendicular) from that 2-D shape to extrude the final 3-D object along.
Are my assumptions right so far?
QUESTIONS ON “EXTRUDE” SECTION OF THE DOCUMENTATION
The first paragraph is followed by 6 bulleted items. I understand the first 2 of the bulleted items. The first describes how the Outside Edge-Loop is selected (i.e., your 2-D shape to extrude). The second bullet seems to describe the “side walls” getting created as you “pull” out the 2-D object into an extruded 3-D object.
Bullets 3 through 6, I totally don’t understand at all. Can anyone explain any or all of them? Maybe re-phrase them? Here are the text of the bullets, followed by my questions:
BULLET (3) TEXT: If the edges in the edge-loop belong to only one face in the complete mesh, then all of the selected faces are duplicated and linked to the newly created faces. For example, rectangles will result in cubes during this stage.
BULLET (3) QUESTIONS: Based on what was stated in Bullet (2), the “side walls” of the selected Outer Edge-Loop have already been created, so we’ve already started the extrusion. So wouldn’t it be Impossible for Any of the edges in the Outer Edge-Loop to belong to only one face? Doesn’t EVERY edge in the outer edge loop now belong to both a face in the flat 2-D surface we’re extruding, AND a “side-wall” of the 3-D extruded object mesh?
BULLET (4) TEXT: In other cases, the selected faces are linked to the newly created faces but not duplicated. This prevents undesired faces from being retained ‘inside’ the resulting mesh. This distinction is extremely important since it ensures the construction of consistently coherent, closed volumes at all times when using Extrude.
BULLET (4) QUESTIONS: What are “the selected faces” referred to in the first sentance? Are those still just the faces that make up the 2-D shape being extruded, or are those all the faces in the entire extruded 3-D object, including the “side-walls”? It says, “the selected faces are linked to the newly created faces…” What does it mean for faces to be “linked”? Does that refer to two or more faces which share one common edge, like the fold in a greeting card is the edge which “links” the front and back rectangular faces of the greeting card? It says, “…but not duplicated.” What does it mean for faces to be “duplicated”? Is that like when you select a mesh object such as a cube and make another copy of that mesh object, so you have two cubes in your scene? That doesn’t seem to make sense here…
BULLET (5) TEXT: Edges not belonging to selected faces, which form an ‘open’ edge-loop, are duplicated and a new face is created between the new edge and the original one.
BULLET (5) QUESTIONS: At this point, I’m totally lost. “Open Edge-Loop”? If it’s “open”, it’s not a “loop”, is it? So lost…
BULLET (6) TEXT: Single selected vertices which do not belong to selected edges are duplicated and a new edge is created between the two.
BULLET (6) QUESTIONS: Ditto.