QTextEdit optimization

[kib2]

Thanks for clarifying this point wysota : is it called by paragraph (group of lines separated by a blank one or more) or by line ?

Edit : it seems it is called by paragraph, right ?

[wysota]

Yes, one paragraph at a time.

[kib2]

In a Qt Quarterly http://doc.trolltech.com/qq/qq21-syntaxhighlighter.html article it is said that :

QSyntaxHighlighter makes this possible through its "state" mechanism. When we finish highlighting a line, we can associate a state with the line (e.g., "Inside C-Style Comment"), which we can retrieve when we start highlighting the following line. The state is stored as an int.

The article is talking about lines, not paragraphs.

So, let's suppose I wanted to highlight comments like this :

### a comment
, maybe on several lines ###

Here 'text' is the QString argument of my highlightBlock method. I put inside some print statements for debugging purpose.

When I call it, having typed : "### a comment", highlightBlock's text returns "### a comment".

After pressing enter and typing the second line : ", maybe on several lines ###", highlightBlock's text returns :", maybe on several lines ###".

So it confuses me : its not a paragraph but the second line only. I expected :
"### a comment\n, maybe on several lines ###".

I must miss something here, but don't know what exactly.

[elcuco]

In QTextDocument (when you load from *.txt files) a paragraph is a line. Maybe that is what's confusing for you.

Now I have a question:
Does anyone know how to query the syntax highlighter for it's state? I want to know the state at a random offset of some random paragraph.

[wysota]

Does anyone know how to query the syntax highlighter for it's state? I want to know the state at a random offset of some random paragraph.

I don't think you can do that. The state is probably saved within the text document itself by using custom user data (probably using QTextBlockUserData). You can check the source code, maybe the data is accessible there, but I wouldn't bet on it. To me the highlighter is only called when appropriate and has no control (nor knowledge) about what happens when it's not called.

[elcuco]

Ok, I started looking at the code:

int QSyntaxHighlighter::previousBlockState() const
{
    Q_D(const QSyntaxHighlighter);
    if (!d->currentBlock.isValid())
        return -1;
 
    const QTextBlock previous = d->currentBlock.previous();
    if (!previous.isValid())
        return -1;
 
    return previous.userState();
}

int QSyntaxHighlighter::previousBlockState() const
{
    Q_D(const QSyntaxHighlighter);
    if (!d->currentBlock.isValid())
        return -1;

    const QTextBlock previous = d->currentBlock.previous();
    if (!previous.isValid())
        return -1;

    return previous.userState();
}

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and d->currenltBlock is defined as:

class QSyntaxHighlighterPrivate : public QObjectPrivate
{
    Q_DECLARE_PUBLIC(QSyntaxHighlighter)
...
    QTextBlock currentBlock;
...
};

class QSyntaxHighlighterPrivate : public QObjectPrivate
{
    Q_DECLARE_PUBLIC(QSyntaxHighlighter)
...
    QTextBlock currentBlock;
...
};

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And I do see that QTextBlock::userState() is public, which means you can know the state of the beginning of a paragraph. Much simpler then I thought of ... even tough it's "not good enough for me".

[wysota]

I'd say it's a bit stupid, because the docs say that setUserState() saves an integer that can be for example used for syntax highlighting. This suggests it can be used for something else effectively breaking the highlighter.

I just read your question again - you wanted the state of a position inside a paragraph. I don't think there is such concept. The state is defined for the position between two paragraphs. I think that instead you can query for the char format of a specified position. It probably won't do you much good either, but maybe you can work something out with it. What is the purpose of such interest?

[elcuco]

Yes, it seems a bug in the Qt4 API, it should be documented that this is 'too fragile" to mess with.

I am toying with the idea of using the syntax highlighter code to know the state of each word in a paragraph. This will help me (for example) knowing which words can I send to a spell checker (only words inside comments or strings for example).

Yes, the variable I showed before only gives me the state in the beginning (or end) or each paragraph.

[kib2]

Thanks elcuco,
for the state, you can use QSyntaxHighlighter::currentBlockState.