Building Layouts - Unity 3D UI Essentials - page 50

Scaling the Rect Transform
A minor but important point to keep in mind with the new Rect Transform
component when scaling: when you scale the Rect Transform it is done
proportionally to the objects Pivot point.
With the Pivot point in the center, the scaling will happen proportionally across
the entire Rect Transform . Move the Pivot point to a corner and the scaling will
be apportioned from the corner where Pivot is.
Something to bear in mind if you're scaling is delivering some
weird results.
This is in effect the same with Rotation , as any Transform will rotate
around its Pivot point. The same is applied for Scaling an object, it gets
scaled by its Pivot point.
The Canvas
As we start to take our first steps with the new Unity UI system, we are welcomed
by one of the first cornerstones of Unity's new implementation, the Canvas .
Put simply, the Canvas (as the name suggests) is your drawing board for all new UI
elements. The legacy GUI system had the GUILayer component attached to a specific
camera. The new Canvas however, has a separate component in its own right that
can (by default) overlay the current rendering scene (as with the legacy GUI), It can
be attached to a specific camera with its own perspective, or even be embedded in
the 3D scene like any other 3D object.
As with many things, you can have more than one Canvas per scene
and can even nest Canvases within each other if you so wish.
Whenever you attempt to add any new UI control to a scene, Unity will
automatically add a base Canvas GameObject into the hierarchy and make your
new UI control a child of the new Canvas. Any new UI elements not parented to a
Canvas will not be drawn to the screen.