I've written a Shell Icon Overlay handler that contains a multi-image icon with 256, 48, 32 and 16 bit icons. The overlay bits are in the lower left corner, and respectively are 32, 15, 10 and 6 bits.
In Windows Explorer, with the View set to Small, the icons are 16 bits and the overlay selected consumes 6 bits. Medium icons: 48 bits overlaid with 10. All as I expected.
When the View is set to Large, a 96 bit icon is used, which is overlaid with 15 bits. Whether this is the 15 bits from the 48 bit overlay, or downsampled from the 256 bit, I can't tell. If I add a 96 bit overlay to the multi-image, using 32 bits for the overlay (just as a test), the overlay used still appears as 15 bits.
When the View is set to Extra Large, the overlay used is still just 15 bits. Just a splotch on a very big icon.
All of the above is on Windows 7. On Windows 8 desktop, the same results are seen, EXCEPT that the Extra Large icon is now only overlaid with a 12*12 bitmap, clearly downsampled from a larger size (15? 32?)
Can anyone help with a definitive answer for what size overlays I should be providing for maximizing the viewing experience?
