Motion Tweening a Mask
In this lesson, we’re going to learn how to animate a mask using a motion tween to change the position of the mask, thus changing the area revealed.
Start off with a new Cool Motion file, and set your scene by drawing something or importing an image to use as the background (or you can easily import the artword from you local computer). On a layer above the layer that will be concealed/revealed by the mask, draw the shape that will delineate the revealed area.
Right-click on the layer set Mask and Masked.
The layers will automatically lock, and you’ll see a portion of your scene through the mask cutout, while the rest is replaced by the stage color.
Unlock the layers so that you can view them normally, then click on the mask shape and convert it to a symbol (F8). Any type will do, but I prefer to use Movie Clips in case later I need to add Action Scripts to them.
Insert keyframes on frame10 and frame20 seperately on both layer.On layer2 frame10, move the mask symbol from its starting to its ending position.
Then, between the first and second keyframe, right-click and select Create Motion Tween (or use the dropdown in the Properties panel) to tween the frames between the starting and ending positions of the motion tween. You can scroll the timeline to watch it move, just like an ordinary movie clip; in truth animating a mask layer is no different from animating a normal layer, because the same rules apply to the shapes used regardless of how Cool Motion is told to interpret their display.
