QTextDocument background colour

[Ruud v A]

Hello everyone,

I am writing a syntax highlighter with QPlainTextEdit, QSyntaxHighlighter and QTextDocument. I want to set the background colour of the editor. I successfully managed to set the background colour of the QPlainTextEdit, and I can set the background colour of individual text blocks with syntax highlighting. However, QTextDocument seems to render a little margin around the text. It renders a white border around the document. Also setting the background colour explicitly every time when highlighting seems unnecessary, it would be better to set the background colour of the entire document. I have tried to use setDefaultStyleSheet but that doesn't work. So how do I set the background colour of a QTextDocument?

Qt 4.6, Windows at the moment but should also apply to other platforms

Thanks in advance,

Ruud

[elcuco]

This needs to be done in a class which derives QTextEdit or QPlainTextEdit. Do this each time the cursor moves:

QTextCharFormat format;
format.setBackground(QColor(0xc0,0xff,0xc0,0x80));
 
QTextEdit::ExtraSelection selection;
selection.format.setProperty(QTextFormat::FullWidthSelection, true);
selection.format = format;
selection.cursor = textCursor();
selection.cursor.clearSelection();
 
QList<QTextEdit::ExtraSelection> selections;
selections.append( selection );
 
setExtraSelections(selections);

QTextCharFormat format;
format.setBackground(QColor(0xc0,0xff,0xc0,0x80));

QTextEdit::ExtraSelection selection;
selection.format.setProperty(QTextFormat::FullWidthSelection, true);
selection.format = format;
selection.cursor = textCursor();
selection.cursor.clearSelection();

QList<QTextEdit::ExtraSelection> selections;
selections.append( selection );

setExtraSelections(selections);

To copy to clipboard, switch view to plain text mode 

The trick is QTextEdit::setExtraSelections() . Download the code of QtCreator for some more hidden gems.

[Ruud v A]

Thanks for the reply! Unfortunately it didn't work. I did find the solution myself after trying some more. The solution was quite simple actually. Instead of setting the default stylesheet for the document, setting the stylesheet of the QPlainTextEdit works:

textEdit->setStyleSheet("background-color: "+colour.name()+";");

textEdit->setStyleSheet("background-color: "+colour.name()+";");

To copy to clipboard, switch view to plain text mode 

[Lykurg]

You could also try to set a proper palette (QPalette::Base). Which is normally a lighter way compared to using style sheets.

[Ruud v A]

I did already set the palette, but that changed only the background colour of the area where there is no text (everything below the last line). The background of the text did not change.

[Lykurg]

Hm, a quick test in designer works for me. But if you are fine with the style sheets, no reason to dig deeper.

[Ruud v A]

It's probably the combination of a QPlainTextEdit with a QSyntaxHightlighter that causes the problem, but you are right, no need to search any further.