Building Objects from Objects

To apply a Pathfinder Panel Click Operation in Adobe Illustrator:

1. Select the overlapping component paths to which you want to apply the operation.
2. Open the Pathfinder Panel (Window > Pathfinder).
3. Click one of the 4 Shape Mode buttons in the top row, one of the 6 Pathfinder buttons in the bottom row, or click the panel's hamburger button to drop down the list of options and click the "Trap…" item to launch the Trap dialog box. Ai will apply the Combining rule to the components. The logic of the combining rules is described below.

Using the result:

• In the Layers panel, Ai will replace (and thereby destroy) the original paths with a single path or with a group of paths.  
• Editing the original Component Paths is impossible because the paths were destroyed.
• Modifying the result is impossible, because the result (the combined path) was not created with a dialog box that can be used to change the combining rule's parameters and because the original paths were not preserved. Therefore, to modify the result, you must recreate the original paths and reapply the effect.
• Reversing the result is also impossible because the original paths were replaced with the result paths.
• Editing the virtual features of the combined paths is unnecessary because the Pathfinder Click operations do not emulate or preview any features of the result. To edit any feature of the result, you simply select one of the resulting simple paths and edit it in the usual way.

To apply a Pathfinder panel Compound Shape (Alt + Click) operation in Adobe Illustrator:

1. Select the overlapping component paths to which you want to apply the operation.
2. Open the Pathfinder Panel (Window > Pathfinder).
3. Alt + click on one of the 4 Shape Mode buttons in the top row. Ai will create a special type of group that contains the original paths and the Shape Mode software will emulate (preview) an appearance that complies with the applicable combining rule. The logic of the combining rules is described below.

Using the result:

• In the Layers panel, you will see a (group-like container, labeled Compound Shape) that contains the original components, which are not destroyed in the process.
• To edit an original component of a Compound Shape, simply select the object in the Compound Shape container, move the object, change its color in the Appearance panel, or Direct Select the anchor points or control handles and edit them.
• Modifying the effect is not possible because there is no dialog box for any of the 4 Shape Mode operations.
• To reverse a Compound Shape operation: go to the Pathfinder panel, click its options menu (hamburger) button, and select "Release Compound Shape."
• To edit a virtual feature of a Compound Shape, you must select the Compound Shape container, and execute the Object > Expand Appearance command. Ai will replace the original paths in the Compound Shape container with equivalent looking simple paths and put them in a new Group. In the process, formerly virtual paths will be converted into real paths. The result will look like the result of clicking a Pathfinder panel button. To edit a path (including ones that were formerly virtual,, select a path in the Group and edit it in the usual way. Note, however, that since the original paths are replaced, they are no longer editable and the Expand Appearance command is not reversible.

To apply a Pathfinder Effect to several overlapping paths in Adobe Illustrator:

1. Select the overlapping component paths to which you want to apply the operation.
2. Group the component paths (Object > Group (Ctrl + g)).
3. Go to the Effects > Pathfinder menu and select an effect.  Ai will:
   1. Preserve the original paths in a group.
   2. Add a row to the Appearance panel representing the Effect, and
   3. Except for the Divide, Trim, Merge and Outline operations, Ai will emulate (preview) the result of applying the appropriate combining rule. The logic of the combining rules is described below.

Using the result:

• In the Layers panel you will see a Group containing the original component objects. When you select that group, you will see in the Appearance panel, a row that represents the Effect, which has a label with the name of the Effect on the left and an fx icon on the right.
• To edit the Component Objects of a Pathfinder Effect: in the Layers panel, simply select the object in the Group, move the object, change its color, in the Appearance panel, or Direct Select the anchor points or control handles and edit them.
• To modify a Pathfinder Effect: in the Layers panel, select the Effect's Group; then in the Appearance panel, click the label of the Effect's fx row. Ai will launch the Pathfinder Effect dialog box. Modify the parameters.
• To reverse a Pathfinder Effect, go to the Layers panel and select the Group to which you applied the Effect. In the Appearance panel, select the Effect's fx row and click the trash can icon at the bottom of the panel.
• To edit a Pathfinder Effect's virtual feature: Target the Effect's Group in the Layers panel. Execute the Object > Expand Appearance command. Ai will convert the Effect's emulated appearance to equivalent looking simple paths and in the Layers panel, will replace the original objects with the new paths. To edit a feature, select any path in the Group and edit it in the usual way. Note, however, that since the original paths are replaced, they are no longer editable, and the Expand Appearance command is not reversible.

To erase faces from selected overlapping paths using Shape Builder in Adobe Illustrator:

1. Select the overlapping paths.
2. Get the Shape Builder tool.
3. Alt + Click or Alt +click + drag through the faces that you want to remove. Ai will remove them and then unite the other faces so that they look like the original overlapping paths, but with the isolated face cut out.

The accompanying illustration shows an example with 3 overlapping paths. In the Before figure, in order to show all the overlapping regions, each circle's Opacity is set to 60% and its blending mode set to Multiply. Ai will analyze these overlapping regions into faces. When one face is deleted, not only does Ai delete that face, but it also reconstructs the original overlapping circles with the deleted face cut out.  The Exploded View shows the structure of the reconstructed circles by moving them apart from one another so that the Multiply blend mode does not show the overlapping regions and thereby hide the form of the reconstructed areas.

Alt +click + dragging or Alt + clicking several times with the Shape Builder is equivalent to the Pathfinder Subtract (Minus Front) operation, which may still be a useful alternative to the Shape Builder when there are many components.

To isolate a face from a set of overlapping paths using Shape Builder in Adobe Illustrator:

1. Select the overlapping component paths.
2. Get the Shape Builder tool.  Ai will analyze the shape into its component faces and edges. As you hover over the faces with the mouse, Ai will highlight them with a gray mesh.
3. Click the face that you want to isolate. Ai will add the anchor points necessary to make the face into an isolated closed path, and them reconstruct the other faces around it, so that the result looks like the original overlapping paths but with the isolated face cut away from them.

The accompanying illustration shows an example with 3 overlapping paths. In the Before figure, in order to show all the overlapping regions, each circle's Opacity is set to 60% and its blending mode set to Multiply. Ai will analyze these overlapping regions into faces. When you click on a face (marked with a X in this example) to isolate it, not only does Ai make the face into a standalone closed path, but it also reconstructs the original overlapping circles with the deleted face cut out. In the After figure, Ai has made the isolated face blue, because you clicked on the blue circle, which was on top of the orange circle. The Exploded View shows the structure of the reconstructed circles by moving them apart from one another so that the Multiply blend mode does not show the overlapping regions and thereby hide the form of the reconstructed areas.

Clicking on faces to isolate them is equivalent to the Pathfinder Divide operation, which may still be a useful alternative to the Shape Builder when there are many components.

To merge faces of overlapping paths using Shape Builder in Adobe Illustrator:

1. Select the original overlapping paths.
2. Get the Shape Builder tool. Ai will analyze the overlapping paths into their component faces and edges. As you hover over the faces with the mouse, Ai will highlight them with a gray mesh.
3. To unite two or more faces, first identify them to the Shape Builder). Either: (A) Click + drag across their boundaries (but do not release the mouse button), or (B) Shift + drag to create a marquee that covers the faces. As you identify the faces, Ai will extend the gray mesh highlight to cover all of them.
4. Release the mouse button. Ai will merge the highlighted faces. That is, it will convert the highlighted faces into a closed path and if necessary, create additional anchor points to create closed paths to represent the remaining, unmerged faces. The Layers panel shows the remaining paths. Some of the new closed paths may contain nested paths. To edit the nested paths, you must double-click them to enter Isolation Mode.

Ordinarily Ai takes the style (fill and stroke) of the merged path from the face where you started the Click + drag operation. You can override Ai's choice of the fill color by using the Pick Color From option in the Shape Builder Options dialog box, which you access by double-clicking the Shape Builder Tool.

Merge is equivalent to the Pathfinder Add (Unite) operation, which may still be a useful alternative to the Shape Builder when there are many components.

To set the Shape Builder tool's options in Adobe Illustrator:

1. In the Tools panel, double click the Shape Builder tool icon . Ai displays the Shape Builder Tool Options panel.
2. In the panel, select an option.

To create a Compound Path from two or more overlapping closed paths in Adobe Illustrator:

1. Select the component paths.
2. Execute the Object > Compound Path > Make command.  Ai will combine the component paths into a single object (as opposed to a Group), and in the Layers panel give it the default label "<Compound Path>".

Illustrator's Object > Compound Path > Make facility does two things:

• If the command is applied to two or more paths that overlap, it excludes the overlapping region from the resulting Compound Path.
• Combines several of the component paths together to create a single path in which the positions of the component paths relative to one another remain fixed.

In fact, you can use Illustrator's Object > Compound Path > Make command to combine several paths into a single rigid object even if they do not overlap, much less define a hole. Thus, while all paths with a hole are represented with Compound Paths, perversely, not all Compound Paths must have a hole.

When two overlapping paths are converted into a Compound Path the result is similar to the result of clicking the Pathfinder panel > Shape Mode area > Exclude button. However, there are two differences:

• The Make method uses the fill of the bottom object, whereas the Exclude method uses the fill of the topmost object to determine the Compound Path's fill.
• The Make method uses the non-zero winding rule, but Exclude uses the odd-even rule to determine the distribution of fills in the areas where the components overlap.

Once you make the original component paths into a Compound Path, you no longer have direct access to them. However, you can enter the Compound Path object by clicking repeatedly on it. This will cause Ai to enter Isolation Mode, as though the Compound Path were a Group. In addition, you can release the components from the Compound Path object.

Fill Rules for Paths that Intersects Themselves

Fill Rules come into play when a path twists around so that it intersects itself. Then the software module that is drawing, or combining objects to create a path needs to know how it should fill the path, i.e., what points it should consider inside or outside of the path.

Illustrator's software modules may use either of two different Fill Rules: the non-zero winding rule and the odd-even rule. The rules are different ways of determining whether a given point on a self-intersecting path, should be considered inside of the path (and should therefore be filled) or outside of a path (and therefore should not be filled).

The Odd-Even Fill Rule tests if a given point is inside or outside of a twisting path as follows. It draws a straight line from the test point to a distant point that is definitely outside of the path and counts the number of times that the line crosses the path. If the number is odd, the point is inside; if the number is even, the point is outside.

The Non-Zero Winding Fill Rule tests if a given point is inside or outside of a twisting path as follows. First it draws a straight line from the test point to a distant point that is definitely outside of the path. Then it counts the number of times the path crosses the line in the clockwise and counter clockwise direction. Each time the path traverses the line in the clockwise direction, it gives point a counts a plus 1. Each time the path crosses the point in a counterclockwise direction, it gives the point a count if negative 1. If the count is zero, the test point is inside the path; if the count is positive or negative, the point is outside the path. The rationale is that if the number of clockwise and counter clockwise turns exactly undo one another other, it makes sense to consider the point outside the path.

 

You can check which fill rule Ai is applying to a particular object by selecting the object and if necessary change the rule by using the Attributes panel.

Releasing a Compound Path is an approximate inverse of creating a compound path, and it works even if the Compound path was not created with the Make command.  

The inverse is only approximate, because while creating a Compound path does not completely destroy the original component paths, neither are they completely preserved and so, they can only be approximately recovered. For example, the original colors are nearly always lost.

Nonetheless, except for paths with holes that were created by a Unite operation, the Release command will recover much of the original paths. Consequently, to edit the original components of a Compound path, you must release the path, reconstruct (e.g. recolor) the original components from the recovered bits, edit the reconstructed components, and then recreate the compound path. 

To release a Compound Path in Adobe Illustrator:

1. Select the Compound Path.
2. Object > Compound Path > Release.  Ai will return the original component objects. For example, if you started with two Ellipses (i.e., Live Shapes), after releasing the Compound Path, you will have two Ellipses, not two normal paths. However, the fills will not return to their former color.