Syntax highlighter to QPlainTextEdit

AndrzejB

Highlighter can also enable code folding? How it implement in highlighter? Code folding can't be implement by regular expression, must be stack?

JonB

@AndrzejB said in Syntax highlighter to QPlainTextEdit:

Highlighter can also enable code folding?

I don't know, but I doubt it. It's a syntax highlighter, not an editor.

AndrzejB

Kf5 extension has folding:
SyntaxHighlighterPrivate::foldingRegion
in
https://invent.kde.org/frameworks/syntax-highlighting/-/blob/master/src/lib/syntaxhighlighter.cpp

JonB

@AndrzejB
Precisely, so why not use it, you are the one who is asking to use plain Qt QSyntaxHighlighter instead.......

AndrzejB

OK, I prefer KF5 Highlighters, but have issues

I want to better know QSyntaxHighlighter and highlighting process
sometimes I need only a few syntax but more control with syntax
if is possible apply QSyntaxHighlighter not only to QPlainTextEdit, but also to other, for example my viewer?
KF5 and Windows? I prefer Linux, but is well to write portable appllcations.

SGaist

Hi,

KF5 is also available on Windows.
Out of curiosity, why not use KDE's KTextEditor ?

AndrzejB

I compiled example from
Qt/Examples/Qt-6.2.4/widgets/richtext/syntaxhighlighter/
In source file Qt/6.2.4/Src/qtbase/src/gui/text/qsyntaxhighlighter.cpp is

void QSyntaxHighlighter::setDocument(QTextDocument *doc)
{
    Q_D(QSyntaxHighlighter);
    if (d->doc) {
        disconnect(d->doc, SIGNAL(contentsChange(int,int,int)),
                   this, SLOT(_q_reformatBlocks(int,int,int)));

        QTextCursor cursor(d->doc);
        cursor.beginEditBlock();
        for (QTextBlock blk = d->doc->begin(); blk.isValid(); blk = blk.next())
            blk.layout()->clearFormats();
        cursor.endEditBlock();
    }
    d->doc = doc;
    if (d->doc) {
        connect(d->doc, SIGNAL(contentsChange(int,int,int)),
                this, SLOT(_q_reformatBlocks(int,int,int)));
        if (!d->doc->isEmpty()) {
            d->rehighlightPending = true;
            QTimer::singleShot(0, this, SLOT(_q_delayedRehighlight()));
        }
    }
}

Where is defined and set "d" variable? It must be PlainTextEditor or can be my own control?
whats is class QTextDocument?

JonB

@AndrzejB said in Syntax highlighter to QPlainTextEdit:

Where is defined and set "d" variable?

From the Q_D(QSyntaxHighlighter); line. See e.g. https://wiki.qt.io/D-Pointer.

It must be PlainTextEditor or can be my own control?

No.

whats is class QTextDocument?

See void QSyntaxHighlighter::setDocument(QTextDocument *doc). It is the document the QSyntaxHighlighter is working on.

AndrzejB

Example of mpergand in thread "How to use scrollbars in my component?" will good start point for exercise.
I wrote simple in-memory text viewer with QScrollArea::
main.cpp

#include <QApplication>
#include <QMainWindow>
#include <QScrollArea>
#include "FileViewer.h"
#include "FileViewer.h"

using namespace std;

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QMainWindow textWindow;
    auto scrollArea=new QScrollArea;

    textWindow.setCentralWidget(scrollArea);

    auto fileViewer=new FileViewer;
    scrollArea->setWidget(fileViewer);

    string filepath = "../main.cpp";

    if(!fileViewer->setFile(filepath))   // file path of your big file
    {
        qDebug()<<filepath.c_str()<<"Error openning the file!";
    }

    textWindow.resize(600, 600);
    textWindow.show();

    return app.exec();
}

FileViewer.h

#ifndef FILEVIEWER_H
#define FILEVIEWER_H

#include <QWidget>

class FileViewer : public QWidget
{
Q_OBJECT
public:
    explicit FileViewer(QWidget *parent = nullptr);
    bool  setFile(const std::string& filepath);
private:
    std::vector<std::string> lines;
    static std::vector<std::string> readLines(std::string filename);
    void  paintEvent(QPaintEvent* ev);
    int _LineHeight;        // height of a line in pixel
};

#endif // FILEVIEWER_H

FileViewer.cpp

#include "FileViewer.h"
#include <QFontMetrics>
#include <QPainter>
#include <QPaintEvent>
#include <QDebug>
#include <iostream>
#include <fstream>

using namespace std;

FileViewer::FileViewer(QWidget *parent) : QWidget(parent) {
    //setVisible(true);
}

bool FileViewer::setFile(const string &filepath)
{
    lines = readLines(filepath);
    // height of a line in the default font
    _LineHeight=fontMetrics().height();
    resize(800, _LineHeight*lines.size());
    return true;
}

void FileViewer::paintEvent(QPaintEvent *ev) {
    QPainter painter(this);
    painter.setPen(Qt::black);
    auto reg = ev->region();
    int originY=reg.boundingRect().topLeft().y();
    int endY=reg.boundingRect().bottomLeft().y();
    int firstLine=originY/_LineHeight;
    int lastLine=endY/_LineHeight+1;
    //qDebug()<<firstLine<<lastLine;

    for(int l=firstLine; l<lastLine; l++)
        {
        const QString str=QString(lines[l].c_str());
            QRect rec=fontMetrics().boundingRect(str);
            /*if(rec.width()+20>_WidestLine)
                {
                _WidestLine=rec.width()+20;
                resize(_WidestLine,_lineCount*_LineHeight);
                }*/

            painter.drawText(QPoint(10,originY+_LineHeight), str);
            originY+=_LineHeight;

        }

    painter.drawRect(reg.boundingRect().adjusted(1,1,-2,-2));
}

vector<string> FileViewer::readLines(string filename)
{
    ifstream infile(filename);
    vector<string> v;
    string line;
    bool readedNewline;
    if (infile.peek() != EOF)
        while(true) {
            readedNewline = std::getline(infile, line).good();
            v.push_back(line);
            if (!readedNewline) break;
        }
    return v;
}

Is maximum simple, only view lines. How to add syntax highlighter? Fileviewer must be descendant of QTextDocument?
Area is repainted even by move window, but not with scroll, how repaint on scroll only needed area?

JonB

@AndrzejB said in Syntax highlighter to QPlainTextEdit:

Fileviewer must be descendant of QTextDocument?

These are two totally separate things. Your FileViewer is a QWidget. A visual thing with scrolling etc.

A QSyntaxHighlighter works on a text document to highlight according to syntax rules. You must supply it with a QTextDocument:

To provide your own syntax highlighting, you must subclass QSyntaxHighlighter and reimplement highlightBlock().

When you create an instance of your QSyntaxHighlighter subclass, pass it the QTextDocument that you want the syntax highlighting to be applied to.

It is then the QTextDocument which you can show in a widget, e.g. a QTextEdit.

Have you looked through https://doc.qt.io/qt-5/qtwidgets-richtext-syntaxhighlighter-example.html ?