Toxicidad del ácido sulfúrico y efectos en la salud

● Now select Modify  >  Mirroring  >  Instance Mirror Toggle .

You’ll notice a very similar eff ect to what we accomplished earlier, with the exception of being able to only edit the original side of the model ( Figure 3.3c ), and that the instanced side can be removed at any time by selecting the Instance Mirror Toggle again. Instance mirroring is often simpler and easier to work with than the symmetry mode described earlier.

Dividing up the Object

Box modeling commands can be roughly classed into two groups: those that help divide the object, and those that help to expand it out and modify it.

Both types of commands add new geometry to the model, which helps you more precisely defi ne its shape. In the next few sections, we cover the three main Silo tools in the box modelers’ arsenal for dividing: Split Loop, Cut , and Bevel .

Split Loop

Split Loop is the easiest and most powerful way to dissect a sequence of connected quads. To get an idea of how it works:

^● Create a cylinder ( Alt  Y ), enter edge selection mode, and select a single vertical edge ( Figure 3.4a ).

● Now select Modify  >  Split Loop or press Shift  X .

You will see a new edge has cut directly through the middle of the selected edge and through all of the quads arranged on a similar track to those on either side of the selected edge ( Figure 3.4b ).

The quads that have been split are known as a face loop (as discussed in Chapter 2), a sequence of quads laid end-to-end, which, as we’ll see later, frequently occur on cylindrical parts of a model (such as arms, legs, fi ngers, or a torso) and connect back on themselves, forming a loop. We will also be Instance Mirror; Modify 

referring frequently to edge loops, which are sequences of edges connected end-to-end that occur on either side of a face loop.

In cases like Figure 3.4 , the split has gone all the way around the object or the entire distance of the loop, but a split might also only travel a short distance.

The direction and length of a loop split can be manually adjusted by selecting the faces you would like to split fi rst. You can select these faces one at a time or automate the process using the Select Loop command ( Selection > Select Loop or Alt  E ) in the following ways:

● Selecting two consecutive faces or a single edge and calling Select Loop will select an entire loop, which can then be split ( Figure 3.5a–c ).

● Selecting two nonconsecutive faces along a loop will select any faces between the two faces, and then calling Split Loop will only split the selection ( Figure 3.5d–f ).

A split can also go along a manually selected group of faces whether they form a true loop or not as long as Silo can calculate a path through the faces ( Figure 3.5g–i ).

The Split Loop command will allow you to adjust the position of the new edges it creates by automatically opening the Slide tool for use on the new edges. This tool lets you slide a sequence of connected edges along the surface of your model as follows:

● If you use the keyboard shortcut to call Split Loop ( Shift  X ), the Slide tool will open and stay active only as long as you continue to hold these keys down.

^● You can adjust the new edges’ position by simply moving your mouse left or right and then releasing the keyboard keys when you are done.

● Otherwise, the Slide tool will open normally after you call Split Loop and you can use it by clicking and dragging on the yellow sphere that appears and pressing Enter or Esc when you are fi nished adjusting the edges.

Cut is a very simple-sounding tool that does many things, depending on what kind of selection you have, but essentially, it lets you divide polygons manually. The important thing to remember about Cut is that it always inserts new edges into the model based on your input and selection mode. Like many tools in Silo, if nothing is selected, Cut will enter an interactive tool mode. If something is already selected, it will act on that selection instead as a command. To get an idea of how it works:

● Go to the menu and select Create > Cube > opt , and in the options screen set all the values to 3. This will give you a cube with nine faces on each side.

FIG. 3.5 Three ways to select and

● Make sure no faces, edges, or vertices are selected, and select Modify >

Cut from the top menu or press X .

You will notice the cursor has changed to a two-tone arrow and, regardless of the selection mode you were in before, you are now in multi-select mode. This is the interactive tool we mentioned earlier. It has an entrance ( X ) and an exit ( Esc or Right Click ), and the program will function much diff erently while the

You will notice you can drag along the edge to place a new vertex. Release the mouse button to complete the placement of the new vertex.

● Now click on a face adjacent to the newly created vertex, and again you will see you can drag the new vertex anywhere within the face ( Figure 3.6c ).

● Finish the cut by clicking on a vertex at the edge of the selected face ( Figure 3.6d ). Press Enter to fi nalize this cut path and start a new one, or press Esc to exit the tool.

It is important to note that a cut cannot jump across an edge between two faces, so to make a continuous cut across multiple faces you must use the tool to cut a new vertex into each edge as you cross it.

As mentioned previously, when vertices, edges, or faces are selected and Cut is called, it will behave as a command rather than an interactive tool, with the following results:

● With two or more vertices selected, Cut will connect any selected vertices that share a face, splitting that face with a new edge.

● With an edge selection, Cut will divide each edge with a new vertex and split any polygons containing more than one of the selected edges by connecting the newly created vertices.

● With a face selection, if a face loop is selected, Cut will divide the face loop.

FIG. 3.6 The Cut tool can be used to cut a path across a model.

Bevel

Bevel is another key tool for dividing an object, particularly useful in working with hard surface objects. The tool is used for creating a bevel along selected edges or the edges connected to selected faces or vertices. It is akin to slicing off the corner where faces meet, revealing a new face and edges, and is frequently used to add a slight rounding eff ect along the corners of an object.

Bevel is also a handy way, as you will see throughout the book, to quickly add geometry to a mesh.

To get a feel for how Bevel works, let’s return to the cube with three subdivisions on each side. will appear that will allow you to adjust the size of the new polygon.

^● You can also press and hold B when performing the initial bevel to adjust the size with the mouse.

The result should look like Figure 3.7b . It is very important to adjust the Bevel in a noticeable way, or it has the potential to create invisible stacks of polygons that will dramatically change how the model looks when subdivided.

Bevel can also be used with faces and vertices, as seen in Figure 3.7a and c . You will notice one problem with using Bevel on faces within a mesh:

it creates triangles at each corner ( Figure 3.7c ). These can be eliminated using the Merge tool, which we discuss later in the chapter.

Bevel Tool; Modify  Bevel; B

FIG. 3.7 The Bevel tool is akin to slicing off a piece of an object and revealing new faces and edges. These screen shots show beveling a vertex, an edge, and a face.