Version:           unspecified (using KDE 4.5.0) 
OS:                Linux

Currently shadows are drawn around a window without respect to their Z-Index. That this calls for is using successively deeper shadows as a window is "higher up". It can easily be accomplished with basic masking, and adds depth and dimension.

Diagram attached:
Top: Z-Indexing
Bottom: Current Method

Reproducible: Always

Steps to Reproduce:
Use composting with shadows.

Actual Results:  
Shadows are not drawn with respect to Z-index

Expected Results:  
Addition of feature would darken and shrink shadows overtop higher windows, getting deeper and fuzzier for lower windows and the desktop, creating a height effect based on Z-index.

This idea moves window shadows from the realm of statically drawn and relatively flat to dynamically drawn.

The Kwin shadow effect plugin would require some additional settings changes to implement this effect.

 - 2 shadow settings would be given, one for shallow and the other for deep shadows. Kwin could have an autoguess setting for the second shadow.
 - If the top window is to be given a glow effect though this plugin still, a third shadow option ("active glow") might need to be considered.
 - Autoguess for deep shadows would likely double the size of the shallow shadow and cut it to 2/3rds intensity.

The actual implementation would likely use the following process to draw shadows;

 1) Bottom window would cast the 'shallow' shadow on the desktop.

 2) The next window up would cast the 'shallow' shadow on the bottom window. The plugin would mix the two depth settings for deep and shallow to create a slightly deeper shadow to cast on the desktop; calculating this by its z-index and the number of windows in total.

 3) Then, repeating step 2, each window would cast the most shallow shadow on the window directly below, using successively deeper shadows as they are cast towards the desktop.

 4) The top window would always cast the deepest setting of shadow on the desktop, still casting the most shallow shadow on the window directly underneath.

 #) If only one window is on the desktop, it would cast a shallow shadow.
 #) When new windows are opened shadows would need to be re-calculated
 #) Some shadows might be kept "dumb" (or have the option) to prevent constant re-rendering. Ie tooltip shadows.
 #) Because the addition of a new window means re-sizing shadows, an option to smoothly re-size shadows should be present to make the change less noticeable.