scrolling Tmemos simultaneously ?

[Etienne_L]

Hi all,

I would like two Tmemos to scroll simultaneously  ( to move in a text and a translation ).

Could be
- catching scrolling events in one Tmemo and propagate them to the other ?
- programmatically setting the starting position of the visible part of the text in the Tmemos, in an event handler of an external, master scrollbar ?

I tried, but did not succeded. Thanks for hints !

Etienne

P.S. Target are windows and linux, but just one platform would already be good help.

[wizzwizz4]

In idiomatic Tcl/Tk, you would solve this by putting both Tmemos in a frame, expanded vertically so they fill all available space (and increase the frame's bounding box as necessary), and attaching a scrollbar to it in the usual manner. Is that approach possible here? Maybe with a TScrollBox?

programmatically setting the starting position of the visible part of the text in the Tmemos, in an event handler of an external, master scrollbar ?

If you take this approach, you also need to set the height of the external scrollbar to the height of the Tmemos if/when that changes. If they have different heights to each other, you need a way to reconcile them: maybe taking the maximum? Depends what you're trying to achieve.

[wizzwizz4]

This feature is implemented in kdiff3, a Qt program written in C++. You might be able to re-use the design. I think the relevant file is difftextwindow.cpp.

[Joanna from IRC]

I believe the original poster who has abandoned thread was asking about tmemo lcl controls in Lazarus

[MarkMLl]

I believe the original poster who has abandoned thread was asking about tmemo lcl controls in Lazarus

I suggest not jumping to that sort of conclusion prematurely, since he might merely be waiting for an answer he understands.

The suggestion of referring to a C++ file in extremis is entirely valid, in the absence of other suggestions.

I've done a little bit of manipulation of TMemo/TRichMemo positioning (in the context of /preventing/ it from tracking program-initiated inserts) but in no way consider myself an expert. In the interest of providing /something/ which might possibly be useful some of the relevant stuff is at https://forum.lazarus.freepascal.org/index.php/topic,67337.msg519191.html#msg519191

MarkMLl

[TRon]

The suggestion of referring to a C++ file in extremis is entirely valid, in the absence of other suggestions.

Indeed but unfortunately those are not very helpful either (other than showing us that it can be done). The diff viewer in double commander (which is written in laz/fpc) does it as well (I haven't looked at its code yet) but those are probably not tmemo's.

The main problem is making it work cross-platform (doing it for windows has many online examples and is fairly simple to accomplish) and I seem unable to 'catch' the scroll-message(s) by using the default hack trickery and adding the scroll-message methods. TMemo uses its own custom scrollbar class so perhaps I overlooked something or am required to overload the Tmemo message-loop itself entirely. I was also unable to locate any relevant example on the forum and/or wiki (specifically aimed for tmemo).

[MarkMLl]

Meld is another, albeit Python :-/

The main problem is making it work cross-platform (doing it for windows has many online examples and is fairly simple to accomplish) and I seem unable to 'catch' the scroll-message(s) by using the default hack trickery and adding the scroll-message methods. TMemo uses its own custom scrollbar class so perhaps I overlooked something or am required to overload the Tmemo message-loop itself entirely. I was also unable to locate any relevant example on the forum and/or wiki (specifically aimed for tmemo).

I was assuming that something like using an external scrollbar to drive the two memos' carets would do the job, but going back and reading OP's "...to move in a text and a translation..." suggests that it's rather more than scrolling since a good translation might reorder fairly large chunks to make the result idiomatic (which again highlights Meld, which is good at such things).

I note that the Wikipedia article on text comparison utilities mentions one being available in the Lazarus IDE (which I don't think I've investigated), but I don't know whether that scrolls two panes: in any event my comment above applies. Updated: it doesn't, it displays diff output in a single pane.

MarkMLl

[TRon]

You are right MarkMLI,

I overlooked that what you emphasized and instead focused on the part "catching scrolling events in one Tmemo and propagate them to the other ? "

Now, the example you linked to makes much more sense 

[MarkMLl]

Now, the example you linked to makes much more sense 

I admit to having a bit of a soft spot for Meld, although I use it rarely. In order to be able to handle reordered text it uses an algorithm by... dagnabbit, can't remember his name but he made himself very unpopular by patenting it and then being a high-profile shill for the "software is patentable" crowd.

The first time I came across this was in about 1990, when I read an implementation coded directly from the original ACM paper. It included the memorable words:

CAUTION: Well-commented code follows. Programmer does not understand what he is doing.

MarkMLl

Updated: Paul Heckel https://dl.acm.org/doi/pdf/10.1145/359460.359467

[Joanna from IRC]

It should be possible to set the tmemo.vertscrollbar.position however I’m not sure how to detect scrolling because I can’t find my o scroll event for either tmemo or its scroll bar. Unless the ondraw or on mousemove events would be used for this. It’s strange that tmemo doesn’t have an on scroll event.

[VisualLab]

In idiomatic Tcl/Tk, you would solve this by putting both Tmemos in a frame, expanded vertically so they fill all available space (and increase the frame's bounding box as necessary), and attaching a scrollbar to it in the usual manner. Is that approach possible here? Maybe with a TScrollBox?

Exactly. That's what TScrollBox is for. It's a matter of setting the height of both TMemo controls (the source text and the translated text) so that the contents of both internal TMemo components scroll evenly. But this is a rather inelegant and makeshift solution.

This feature is implemented in kdiff3, a Qt program written in C++. You might be able to re-use the design. I think the relevant file is difftextwindow.cpp.

In this case, it is rather a control class specially prepared for this purpose that is used. A similar solution is used in NetBeans to visualize differences between two files (but it is Java code). I also remember that about 10 years ago I came across a program written in Delphi, which was used to compare PAS files. It is possible that somewhere in the depths of the Internet there is available the code of the control used in this program.

[MarkMLl]

It should be possible to set the tmemo.vertscrollbar.position however I’m not sure how to detect scrolling because I can’t find my o scroll event for either tmemo or its scroll bar. Unless the ondraw or on mousemove events would be used for this. It’s strange that tmemo doesn’t have an on scroll event.

It might be possible to "surface" something from a superclass.

MarkMLl

[dbannon]

You cannot be sure that a translation will use the same number of lines as the original. So, I don't think having an external "scroll control" and applying it to both tmemos or make one a slave to the other's scrolling would work. As you scroll down, they will get out of sync.

You need a key or token in both in the content and drive the second TMemo to display the same token. But doing that unobtrusively will not be easy. Using KMemo (or, maybe TRichMemo) would allow you to embed invisible tokens between, for example, paragraphs. But big paragraphs ...

I am guessing that the user expects to type into one or both TMemos ? And could delete a token...

If both are read-only, easy, just put a "para 1" token between every para, ugly but effective. I would not use it !

Davo

[VisualLab]

You cannot be sure that a translation will use the same number of lines as the original. So, I don't think having an external "scroll control" and applying it to both tmemos or make one a slave to the other's scrolling would work. As you scroll down, they will get out of sync.

You need a key or token in both in the content and drive the second TMemo to display the same token. But doing that unobtrusively will not be easy. Using KMemo (or, maybe TRichMemo) would allow you to embed invisible tokens between, for example, paragraphs. But big paragraphs ...

I am guessing that the user expects to type into one or both TMemos ? And could delete a token...

If both are read-only, easy, just put a "para 1" token between every para, ugly but effective. I would not use it !

Davo

Based on your idea, I came up with an idea (quickly) to create my own classes (2):

• a data container (component) that stores the content (original and translation) and tokens associated with it,
• a display field (control) consisting of 2 vertical sections (original, translation) of the content visualization,
• each of the 2 content visualization sections is a view that retrieves content from the container, displays only text but is aware of tokens,
• the display field (control) contains a vertical synchronous content scroll bar that uses tokens.

Of course, the given idea has some drawbacks. For example, when the user removes a piece of content from one or the other section, you need to take care of correct updating of tokens and the scroll bar.

This is a rather time-consuming solution and requires some experience in writing controls.

[Joanna from IRC]

The problem of translation not having same number of lines could be solved by adding extra line to translation or original. 

It seems that this would only be a good for readonly memos . Also is there a way to track what the index of first visible string in memo. Another thing, it’s possible that there are no line breaks but text wrapping and the whole thing could be one string?