Re: Saving selection into undo history

I’m looking at this to replace our application level selection undo history and it seems to work, but we save the scroll position (the first visible line). Any chance the scroll position could be added? If not, we might track this in the application or continue using our implementation.

Could there be an option to delete the ModelState for a view? We create more that one view if the document is visible in more that one widget and then destroy the extra views when the widgets are destroyed.

Thanks,

John

> On Feb 2, 2025, at 12:31 AM, Neil Hodgson <[email protected]> wrote:
> 
>    There's an updated version of this feature that fixes some bugs and uses less memory.
> 
>    Instead of an 80-byte (plus at least 40 bytes of linked data) SelectionSimple structure based on the Selection structure used for the active selection, selections are saved in a text form that often takes 24 bytes. A single selection from positions 12 to 34 with 5 virtual spaces may look like "12-34v5". There's provision for multiple selections and rectangular selections and some other details.
> 
>    This string format is also an easy way of storing the shape and ranges of selections when switching documents so there are new APIs SCI_GETSELECTIONSERIALIZED and SCI_SETSELECTIONSERIALIZED and SciTE now uses them. I'm a bit conflicted on these APIs as they are convenient but not strictly necessary which is something I've tried to avoid in Scintilla since expanding the API scope adds to maintenance costs. Exposing a 'little language' for selections raises concerns with maintaining compatibility so, for now, they are documented for use within a session but the format may change between Scintilla releases. Search SciTE for "SelectionSerialized" for some example code.
> 
>    One of the issues that scared me off implementing undo selection history earlier was that selections are view state and there may be multiple views on a document. The implementation places this data in the Document indexed by the view (EditModel object). This works by adding a ViewState base class to Document.h then each Document holds a map of void* to shared_ptr<ViewState> where the void* is actually the address of the view object. The EditModel then defines a ModelState subclass of ViewState to hold any data (currently just the undo selection history) that the view needs to associate with a Document. That allows the view to retrieve the history whenever a Document is attached to that view.
> 
>    There is a TruncateUndo method on ViewState that allows the Document to tell the ViewState/ModelState that undo steps have been deleted so it can delete any selections associated with the steps. That was a problem during development as I initially wanted a mechanism that could be implemented in the application if the application had more needs (like associating explanations with undo steps) but that was more difficult. Because shared_ptr is used, the ModelState will be freed when the Document is freed. However, if a Document is still live but a view is deleted then the ModelState for the view is not freed. This case should be rare in practice as most applications have simple view lifetimes - either a separate view is allocated for each document or a fixed set of views are created that switch between documents. It could be fixed with a central repository of View/Document relationships but sharing more state between subsystems looks like a jump in complexity to me.
> 
> The committed changes can be examined either in the repositories
> 
> hg clone http://hg.code.sf.net/p/scintilla/code scintilla 
> hg clone http://hg.code.sf.net/p/scintilla/scite 
> 
> or from 
> 
> https://www.scintilla.org/scite.zip Source 
> https://www.scintilla.org/wscite.zip Windows executable (64-bit) 
> 
> Neil
> 
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