Using the following transform produces an unscrollable scrollbar if inside a self-sizing viewport:

[JSearUK]

transform HoverSpin:
    on selected_hover, hover:
        linear 1.0 rotate 359
        rotate 0
        repeat
    on selected_idle, idle:
        rotate 0

[JSearUK]

@KiloOscarSix This is one of the issues I ran into in my original mod. I'm pretty sure it'll take Tom/the Ren'Py team to officially fix this one, though you'll probably be able to find the problem and submit a patch to them

[JSearUK]

I'm going to try explicitly setting the size of the imagebuttons, to see if that cheers the viewport up..?

• Explicitly setting the imagebutton xysize (30, 30) had no effect
• Adding rotate_pad True to the transform had no effect
• Doing both of the above at once had no effect
• Note: defining enable_animation = True, thus setting at HoverSpin on the imagebutton, seems to expand horizontal spacing compared with enable_animation = False, which merely sets hover_background to Solid(gui.text_color) (instead of None). There is definitely something going wrong with calculated sizes somewhere.

[JSearUK]

I've found the problem, and applied a workaround. Issue has been forwarded to RenpyTom, who added it as an Issue, here: https://github.com/renpy/renpy/issues/2987 Closing this.