The pan behind tool in After Effects lives in the shadows of more used tools such as the select tool and the type tool. It’s not that it doesn’t get used that much, but the ambiguity of the tool with its parenthetical (anchor point) always feels like it’s an afterthought. On one hand, we can move an anchor point around which is helpful. On the other, we can use the tool to move the footage or image of a masked layer without affecting the mask. This is actually super helpful, but you’re not going to use it to do something cool, right? Wrong.
It’s Not the Tool’s Fault
Probably a big misunderstanding about the panning part of the tool is that it feels like you’re just changing the position of the layer while the mask remains unchanged. In reality, you’re actually moving the mask along with the position of the layer. It kind of works like the unified camera tool in the sense that it’s controlling two properties at once. So, if you’ve ever tried to keyframe the footage position and used the pan behind tool you probably became frustrated with the results.
“Why is the mask moving? I didn’t even touch the mask. This is ridiculous!”
After that, you probably figured out another way to do what you wanted or abandoned the idea altogether.
Sprite Sheets are Fun
A good example of using the pan behind tool to aid in animation is dealing with sprite sheets. A sprite sheet is an image that contains several frames of an intended animation. Perhaps you used an illustration program like Photoshop or Illustrator to do some frame-by-frame animations. Instead of trying to create layers to export frames, you could just put each frame next to the previous one in a grid or row.
Once you import the sprite sheet into After Effects, position the first sprite where you want the animation to take place in your composition. Next, draw a mask around your first sprite, thus hiding the rest. Now, it’s time for the pan behind tool to shine!
Let The Pan Behind Tool Do The Work Of Two Tools
Create a keyframe for the position of your layer and a keyframe for the mask path. Use the page down key on your keyboard to advance to the next frame in your timeline. Use the pan behind tool to position the next sprite within the mask. You’ll notice that when you do this a keyframe is created for both the position and the mask shape.
Continue adjusting the sprite sheet with the pan behind tool and advancing to the next frame until you reach the end of your animation. If you need to make any adjustments to your mask, use the pen tool or selection tool. You won’t mess anything up because you’re already making a keyframe for every frame. Now you can preview your animation and admire how wonderful the tool is.
Keep in mind that if you need to reposition your layer animation in your composition, you need to select all of the keyframes for the position property. They will all be yellow instead of gray. You can now adjust the position property values until you are happy with the new placement. Any adjustments will affect all of the keyframes instead of just one.