How to navigate QPlainTextEdit / QTextBrowser

Violet Giraffe

I have a long QString (plain text) and an index for it. Say, the string is a book and I know where each chapter starts in it. The string is displayed using QPlainTextEdit (or maybe QTextBrowser - doesn't matter much, it's just that scrolling huge text is smoother in the former).

How can I navigate between chapters in the text viewer? I know I can use QTextCursor to go to a specific line in the widget, but knowing line numbers for the source string will do me no good since there are huge paragraphs and line wrapping will engage, so I have no way of knowing how the source string's lines will correspond to the view's lines.

Ideas?

Can I use hypertext (which was more or less designed just for this)? Rich text and anchors?

VRonin

You can indeed use QTextCursor.
assume QPlainTextEdit * plainTextEdit and you want to reach the character at position int charIndex

plainTextEdit->moveCursor(QTextCursor::Start);
for(int i=0;i<charIndex;++i)
plainTextEdit->moveCursor(QTextCursor::NextCharacter);

Violet Giraffe

@VRonin
That's easy enough! Won't it be slow when I have to move to the character number 1 million?

VRonin

If it is you can try:

plainTextEdit->moveCursor(QTextCursor::Start);
QTextCursor txtCur=plainTextEdit->textCursor();
txtCur.movePosition(QTextCursor::NextCharacter,QTextCursor::MoveAnchor,charIndex);
plainTextEdit->setTextCursor(txtCur);

but I suspect that internally the same thing happens to the cursor as the for loop case

Violet Giraffe

@VRonin
I suspect the widget updated is queued every time, and the question is whether or not 1 million updates will collapse into one. I'll know soon enough. Regardless, the second version looks cleaner to me, even though it's more verbose.

Violet Giraffe

@VRonin
It works! Except with a 1.58 million characters Unicode text executing movePosition(QTextCursor::NextCharacter,QTextCursor::MoveAnchor,charIndex) takes the longer the larger charIndex gets. In the end it reaches 4.0 seconds on my core i5-2500 CPU @ 3.8 GHz.
But I don't suppose something can be done about that?..

Violet Giraffe

Fixed the problem. QTextCursor has a method setPosition that works instantly. So instead of

txtCur.movePosition(QTextCursor::NextCharacter,QTextCursor::MoveAnchor,charIndex);

I simply did

txtCur.setPosition(charIndex);

And now there's no performance issues.