I know the principles of masking a layer so thats covered. However i'm having issues with the following:
I have three layers....
Layer 1 - BOTTOM) a Red line draws upwards towards a Blue box and disappears behind it
Layer 2 - MIDDLE) a static Blue box
Layer 3 - TOP) As if continuing from layer (1) the line now appears inside the Blue box and continues to draw upward only now the line has magically changed colour to Black.
I thought I could apply a mask on layer (3) - the inner Black line which would be masked in the shape of the box, The aim was to crop the animating Black line to ensure it remains within the confines of the box. However, as im moving the line inside the box the mask insists on moving with the animation instead of remaining static.
How do I create a static mask that can 'isolate' content thats animating in and out of the mask
PS - Im using AE CC 2014 on a Mac
Read up on how to use matte layers.
You may be approaching the problem in the wrong way to start with. I'm in the middle of producing a tutorial but I'll share the project file and a screenshot. See if these techniques will help. (Note: Some browsers add a .txt extension to the AE file name. Just remove the extension and keep the .aep and the file should open)
I think I was along the right track but I had a few things back-to-front. However, your files were really helpful. Thank you.