Racking my brain for a way to have the opacity on an object, say a rectangle, "fall off" from the top to the bottom of the rectangle. So, in other words, the top of the rectangle is at 100% opacity, and the bottom is at 20% opacity, with the areas in the middle falling off gradually like a gradient. Any ideas?
Sure - use an image mask. First, create a shape and fill it with a black and white gradient running vertically. The, select your rectangle, and choose Object > Add Image Mask. Drag the gradient to the well in the HUD (or even directly onto the image mask in the Layers tab). Set it to Luminance. Adjust the gradient to taste using the interactive gradient tool in the Canvas.
Apple-certified instructor, FCP, DVDSP and Motion
Author, Motion Visual Quickstart Guide from Peachpit Press http://www.applemotion.net