Draw rich text with QPainter

Question

is there a way to draw fixed text that has subscripts. My goal is to have something like: "K_max=K_2 . 3"

QString equation="K_max=K_2 . 3";
painter.drawText( QRect(x, y , width, y+height), Qt::AlignLeft|Qt::AlignVCenter, equation);

I also tried formatting the text using html tags but it didn't help (tags got printed with the text):

QString equation="<p>K<sub>max</sub></p>=<p>K<sub>2</sub></p>.3"

You can show it in a QLabel, like: `QLabel lbl("
K_max
=
K₂
.3"); lbl.show();`. — vahancho, Apr 27 '15 at 09:59
Thanks for your answer, but I'am trying to print the text to a pdf file using QPrinter as a paint device — luffy, Apr 27 '15 at 10:11
You can set that html code to a label, than grab the label's content as a pixmap and paint the text as an image with your printer. Otherwise there is no such function that supports drawing formulas. — vahancho, Apr 27 '15 at 10:23
Try using unicode. Qt usually work good with it: https://en.wikipedia.org/wiki/Unicode_subscripts_and_superscripts — Amartel, Apr 27 '15 at 10:59
@vahancho you wrong, there is such function. Check my answer. — Dmitry Sazonov, Apr 27 '15 at 11:14
@Amartel thanks. I tried using unicodes and it worked for defined characters but the "m" for example is missing — luffy, Apr 27 '15 at 12:10

Mykhaylo Kopytonenko · Accepted Answer · 2015-04-27T12:35:40.207

31

Here is a full example using rich text of QTextDocument.

mainWindow.cpp:

#include "mainWindow.h"

void MainWindow::paintEvent(QPaintEvent*)
{
    QPainter painter(this);
    QTextDocument td;
    td.setHtml("K<sub>max</sub>=K<sub>2</sub> &middot; 3");
    td.drawContents(&painter);
}

If you need to draw the text at specific point, translate the coordinate system of the painter before drawing:

painter.translate(QPointF(50, 50));

mainWindow.cpp - Another solution:

#include "mainWindow.h"

void MainWindow::paintEvent(QPaintEvent*)
{
    QPainter painter(this);
    QTextDocument td;
    td.setHtml("K<sub>max</sub>=K<sub>2</sub> &middot; 3");
    QAbstractTextDocumentLayout::PaintContext ctx;
    ctx.clip = QRectF( 0, 0, 400, 100 );
    td.documentLayout()->draw( &painter, ctx );
}

mainWindow.h:

#include <QtGui>

class MainWindow: public QWidget
{
protected:
    void paintEvent(QPaintEvent*);
};

main.cpp:

#include <QtGui>
#include "mainWindow.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MainWindow mainWindow;
    mainWindow.show();
    return app.exec();
}

The project file:

TEMPLATE = app
QT += gui
HEADERS = mainWindow.h
SOURCES = main.cpp mainWindow.cpp

Result:

enter image description here

edited Apr 27 '15 at 12:35

answered Apr 27 '15 at 11:17

Mykhaylo Kopytonenko

923
7
15

You have memory leak in `main`. But thatnks for writing samples to my answer :) – Dmitry Sazonov Apr 27 '15 at 11:34
1

Thanks, I tried this and it works fine for the position (0, 0), but as soon as I try to move the text to a predefined position in the page ("ctx.clip = QRectF( x, y, 400, 100 );") it disappears! Any ideas how I can fix this ? – luffy Apr 27 '15 at 12:15
1

Edited my answer to include this case. In brief, translate with "painter.translate(QPointF(50, 50));". – Mykhaylo Kopytonenko Apr 27 '15 at 12:36
If I need to draw at a specific point, isn't there any other way to do that than to translate the `QPainter` object? Maybe I have received a `QPainter` object as a function argument but have declared the argument `const`; then I won't be able to translate it. (A `QPainter` object cannot be copied either.) – HelloGoodbye Oct 07 '16 at 12:18
Any way to translate with a specific base line. For example I want my base line to be at (10,50), but translating it to (10,50) renders the text at (14,75). I now have trouble aligning text drawn with drawText. – RvdK Jan 25 '17 at 10:26

score 6 · Answer 2 · answered Apr 27 '15 at 11:09

6

You may use supported Qt HTML subset to format your text. If you need to draw formatted text, you should use QTextDocument::drawContents.

QPainter::drawText is designed for plain text without formatting, and it works much faster.

answered Apr 27 '15 at 11:09

Dmitry Sazonov

8,801
1
35
61

score 2 · Answer 3 · answered Jun 09 '22 at 20:10

Since Qt 4.7, you can use QPainter.drawStaticText() with QStaticText:

painter = QPainter()
top_left = QPoint(0, 0)
painter.drawStaticText(top_left, QStaticText('foo<b>bar</b>'))

QStaticText will attempt to guess the format of the input text using Qt::mightBeRichText(), and interpret it as rich text if this function returns true.

If the limitations of QStaticText suit you (see class description), it should be much faster than QTextDocument.

Draw rich text with QPainter

3 Answers3

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