Add transient visibility mode for empty containers

When you add a new container, such as a LinearLayout, it is usually
invisible. The reason for this is that an empty layout has 0 width and
0 height. There are two existing features in the layout editor to deal
with this: (1) Outline mode, which renders rectangles around all
views, and (2) Padding mode, which adds 10 pixels of padding to all
views. In combination, these two modes will create a rectangle for
empty layouts making them visible and user-manipulatable -- you can
for example select or drop into them.

This changeset attempts to make dealing with these types of containers
easier and more discoverable. It adds a new temporary mode where empty
containers (and only empty containers) are automatically padded and
have their outlines painted. And more importantly, this is only done
in some limited scenarios: When you drag into, or drag within, the
layout canvas. As soon as you finish the drag, empty containers
disappear again.

Unlike padding mode, we don't enlarge the design surface itself, since
this mode comes and goes easily and frequently.

In addition to this, there is special handling for selection. If you
select a zero-sized element (which for example is automatically done
when you drop a new layout, and which can also be done by clicking in
the outline), then the element is also revealed similar to the
show-empty mode, but in this case only the selected item and not any
other invisible containers are shown.

Change-Id: Ibf3ec6a080a50a8f0f55919c3d3e6c4d2890468d

1 files changed, 7 insertions, 1 deletions

diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/common/api/DrawingStyle.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/common/api/DrawingStyle.java
index 335e565..0938afa 100644
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/common/api/DrawingStyle.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/common/api/DrawingStyle.java
@@ -91,11 +91,17 @@ public enum DrawingStyle {
     HELP,
 
     /**
-     * The style used to raw illegal/error/invalid markers
+     * The style used to draw illegal/error/invalid markers
      */
     INVALID,
 
     /**
+     * The style used to draw empty containers of zero bounds (which are padded
+     * a bit to make them visible during a drag or selection).
+     */
+    EMPTY,
+
+    /**
      * A style used for unspecified purposes; can be used by a client to have
      * yet another color that is domain specific; using this color constant
      * rather than your own hardcoded value means that you will be guaranteed to