On a long script (~11k words in this case) is it normal to have a delay in response when attempting to adjust the font size slider?
That is the case for now, yes. QPrompt can handle a little over 36 hours of text without crashing, but the font size handle become slow long before because all glyph dimensions need to be recomputed for all text to be placed correctly.
If this is too much of an issue, there are a couple of ways in which the editor/prompter’s implementation could be improved for that not to happen. It’s one of those features that require a lot of work for small gains that go underappreciated, and the solution still wouldn’t fully eliminate the delay.
The solution that I have in mind is to re-implement Qt’s TextEditor component such that previous glyph sizes are cached instead of deleted when the text is re-sized. This wouldn’t prevent the initial delay, but it would prevent the delay from happening if you move the slider back to a previous position, reducing the total amount of delay when trying to make a precise font size adjustment, as each size would only have to be processed once.
An ideal solution would be to resize only the elements on screen first, and compute the rest after the user lets go of the slider. Unfortunately I have no idea of how to implement that at the time. I would likely have to develop the character engine from scratch.