|  |  | 7.2 Views

## 7.2 Views

When making a PDF presentation with Acrobat Reader, one would often like to present a page incrementally. For instance, I would first like to show a polygon, then add its triangulation, and finally color the vertices. Views make it possible to do this nicely.

An Ipe document consists of several pages, each of which can consist of an arbitrary number of views. When saving as PDF, each view generates a separate PDF page (if you only look at the result in, say, Acrobat reader, you cannot tell whether two pages are actually two views of the same Ipe page or two different Ipe pages).

An Ipe page consists of a number of objects, a number of layers, and a number of views. Each object belongs to exactly one layer. A layer can be shown by any number of views—a view is really just a list of layers to be presented. In addition, a view keeps a record of the current active layer—this makes it easy to move around your views and edit them. Finally, views can specify a graphic effect to be used by the PDF viewer when proceeding to the following PDF page.

To return to our polygon triangulation example, let's create an empty page. We draw a polygon into the default layer "alpha." Now use the New layer, new view function (in the Views menu), and draw the triangulation into the new layer "beta." Note that the function not only created a new layer, but also a second view showing both "alpha" and "beta". Try moving back and forth between the two views (using the PageUp and PageDown keys). You'll see changes in the layer list on the left: in view 1, layer "alpha" is selected and active, in view 2, both layers are selected and "beta" is active. Create a third layer and view, and mark the vertices.

Save in PDF format, and voila, you have a lovely little presentation. The result is available here.

In presentations, one often has slides with mostly text. The textbox object is convenient for this, as one doesn't need to use the mouse to create it. To create a slide where several text items appear one by one, one only needs to press F10 to create a textbox, then Shift+Ctrl+I to make a new view, F10 again for the next textbox, and so on. Finally, one moves the textboxes vertically for the most pleasing effect (Shift+Alt+Left Mouse does a constrained vertical translation, or Shift+Left Mouse in Translate mode).

Note that all views of a page receive the same bounding box, containing all objects visible on some view, plus all objects in a layer named "BBOX" (even if that layer is not visible). This can be used to force a larger bounding box without adding a white rectangle or the like.

If you need independent bounding boxes for each view, create a layer named "VIEWBBOX". Any view in which this layer is visible will receive a bounding box computed for the objects visible in this view only.