Shapes

Draw a shape and keep what is inside it — a garbage matte, a split screen, a window for a graphic. Drag the points on the picture, and keyframe one to make it follow.

Shape keeps what is inside a drawn outline and drops everything else. It is the effect you reach for when a key has left a light stand in shot, when two shots need to share the frame, or when a graphic needs a window to sit in.

Drawing one

Drop Shape on a shot from the Effect Palette, then press Drag the points on the picture.

• Drag on the picture and a rectangle comes out — which is what a garbage matte almost always is.
• Shift-drag to draw freehand: trace round whatever it is and let go. The outline is thinned to the corners you actually drew rather than every wobble of the mouse.
• Click to place a single point, for drawing a polygon one corner at a time.
• Drag a handle to move it.
• Click a side of the outline to add a point there — which is how you fix a corner you drew too early, without the outline crossing over itself.
• Double-click a handle to take it out.

Dragging out a new shape replaces the old one; clicking a side adds to it. So "this shape instead" and "one more point here" are different gestures and neither can be mistaken for the other.

A shape with fewer than three points does nothing at all — an effect you have just added and not drawn is never allowed to change the picture, and while it is under three the frame says how many more to place. Twenty-four points is the most one shape holds; a shape that wants more is two shapes.

Feather, and keeping the outside instead

Feather softens the edge. It is a ramp across the outline, half inside and half out, so a feathered shape does not shrink as you soften it.

Keep the outside instead inverts it: everything outside the outline stays and the inside goes. That is the setting for painting out a sign — put the shape on the sign and invert.

Making it follow

Every point is a number, and every number keyframes. So a shape follows a face the same way anything else in B/side moves: park on the frame where it is right, move it, and it keyframes.

Move X and Move Y shift the whole shape at once. Keyframe those two rather than seventeen points and a hand-drawn mask follows a moving shot for the price of two curves.

A shape in the master

The shape renders. The picture you see in the monitor and the picture in the deliverable are made from the same mask — not two implementations of one outline that agree most of the time — so an edge that looks right on screen is the edge that goes out (§12).

Shapes that come from Avid

An AniMatte imported from an Avid bin arrives as one of these, with its points already in place: B/side reads Avid's own shape data out of the bin rather than asking you to redraw it.

Two honest limits. The scale Avid stores a shape in is not yet calibrated against the frame, so an imported shape can arrive at the wrong size until that is settled — drag a point and it is yours. And B/side does not write Avid's shape format back out: going the other way, an AniMatte is a note telling the online house what to redraw, because generating a file that claims to be Avid's own is something B/side will not do.