With the kind permission from Hyperion, I recently uploaded the V45 version of layers.library to aminet.
Layers.library is responsible for the "slice & dice" operations required for window re-arrangements, computes cliprects, damage regions and provides the backing-store for "smart-refresh windows".
Layers (up to v40, Os 3.1) was considerably ill-designed for rtg (regargetable graphics, graphics cards) and thus was heavily patched to avoid performance degrations.
The V45 release is an old code that collected dust here on my harddisk which was created as input for Os 4 - and in fact, is the Os 4 version is based on the V45 release.
Besides a major cleanup of the Os 3.1 version of layers (v40), the optimizations for graphic cards and the improvements in memory management, this release also provides new functionalities to hide and show layers, for example to allow window iconification with little or no extra efford from software. The uploaded archive contains a "tech demo" (amisnip) that demonstrates the functionality. Note that Amisnip is a technology demo, not a "good program". Sources are included to inspire authors.
V45 layers also includes support to automatically clip layers at layer_info boundaries, another new functionality. With a proper modification of intuition (which is of course not available), this would allow to easily drag out windows from the screen - something that was not possible before either. There is another technology demo in the archive that shows how to enable the feature (without enabling the drag-out of windows, which is as said something to be done in intuition).
Note well: This is all for classic Amigas. Os 4 has the features anyhow, and (partially) by the same author, and is based on the same code basis. Thus, you loose nothing with Os 4 - you already have it.