I’ll see if I can make a diagram which explains how it’s constructed. In the mean time these are the basics:

For the Cylinder:

• Per scanline Y scroll adjustments from a pre-computed table (made in a spreadsheet) that create the cylinder distortion.
• There is a matching set of per scanline GB palette adjustments which darken the colors toward the top and bottom of the cylinder.

For the bounce:

• There’s a per-frame sine wave table that adjusts where the cylinder is located (by setting an initial Y scroll offset which the cylinder code factors in).

For the Text:

• The entire cylinder only uses Background (BG) colors 1-3, and the area outside of it is all scrolled to a single line which only uses BG color 0. This is important for the next part:
• For hiding the text that goes “behind” the cylinder the sprites on the left 1/4 and right 1/4 of the screen have their BG priority set so that they only show up over BG color 0 (above and below cylinder area) and are hidden by anything with BG color 1-3 (inside cylinder area).
• Then there is a second sine wave table which is used for the text Y position, this is just indexed based on the sprite X position