How can I replce Qpainter::drawText with a more effecient way to draw text in a table cell

xce1

@jsulm
I use VS2019 IDE, with multibyte charset and need show some chinese characters.

I just tried QString::(txt.c_str()), still has the problem.

jsulm

@xce1 There is no need for txt.c_str() at all! txt is already a QString which is UTF-16 and can handle Chinese.

xce1

@jsulm
Thanks for your attention, but txt is really a std::string.
The other parts of the program uses c++ std lib mostly, so here I used std::vector<std::vector<std::string>> contents; to store cell strings.

I just upload the gif, which shows what I described as drawText is slow.
Would you help me with that?

Best regards.

jsulm

@xce1 https://doc.qt.io/qt-5/qstring.html#fromStdString

xce1

I've replaced all std::strings to QString, and change VS2019 charset to utf, and only use ASCII chars in string.
Still there is a visible blank before the custom tables shows.

Even there is only one column， one row.

JonB

@xce1
Your post is hurting my eyes! :( :)

xce1

I've tested it with a single drawText call in paintEvent, the problem still exists.
But if I put a label on widget, the problem disappears!
main.cpp

#include <QtWidgets/QApplication>
#include "QPlainStyleTable.h"
#include "QtClass.h"

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

//     auto _m_pTable = new QPlainStyleTable();
//     _m_pTable->SetHeaderColor(Qt::red, Qt::green);
//     _m_pTable->SetContentColor(Qt::gray, Qt::yellow, Qt::blue);
//     _m_pTable->SetBorderColor(Qt::white);
//     //_m_pTable->SetFont(QFont(u8"微软雅黑"), QFont(u8"微软雅黑"));
// 
//     _m_pTable->SetDimension(1, 1);
// 
//     _m_pTable->SetTitle({ "a", "b", "c", "d", "e" });
//     _m_pTable->AddData({ "a1", "b1", "c1", "d1", "e1`" });
//     _m_pTable->AddData({ "a2", "b2", "c2", "d2", "e2" });
//     _m_pTable->AddData({ "a3", "b3", "c3", "d3", "e3" });
//     _m_pTable->AddData({ "a4", "b4", "c4", "d4", "e4" });
//     
//     _m_pTable->show();
    auto _m_pQClass = new QtClass(nullptr);
    _m_pQClass->setFixedSize(500, 400);
    _m_pQClass->show();
    return a.exec();
}

QtClass.h

#pragma once

#include <QWidget>

class QtClass : public QWidget
{
    Q_OBJECT

public:
    QtClass(QWidget *parent);
    ~QtClass();

    void paintEvent(QPaintEvent* e) override;
};

QtClass.cpp with QLabel commented out.

#include "QtClass.h"

#include <QPainter>
#include <QLabel>

QtClass::QtClass(QWidget *parent)
    : QWidget(parent)
{
//     auto _pLabel = new QLabel(this);
//     _pLabel->setText("HELLO WORLD!");
//     _pLabel->move(200, 300);
}

QtClass::~QtClass()
{
}

void QtClass::paintEvent(QPaintEvent* e)
{
    QPainter painter(this);
    painter.drawText(0, 0, 100, 200, Qt::AlignCenter | Qt::TextSingleLine | Qt::TextDontClip | Qt::TextWordWrap, QString("Hello World!"));
}

QtClass.cpp with QLabel .

#include "QtClass.h"

#include <QPainter>
#include <QLabel>

QtClass::QtClass(QWidget *parent)
    : QWidget(parent)
{
    auto _pLabel = new QLabel(this);
    _pLabel->setText("HELLO WORLD!");
    _pLabel->move(200, 300);
}

QtClass::~QtClass()
{
}

void QtClass::paintEvent(QPaintEvent* e)
{
    QPainter painter(this);
    painter.drawText(0, 0, 100, 200, Qt::AlignCenter | Qt::TextSingleLine | Qt::TextDontClip | Qt::TextWordWrap, QString("Hello World!"));
}

xce1

@JonB Sorry about that. I've removed the colorful gifs.

@jsulm Perhaps It's not drawText problem.
To better demonstrate the situation, I've upload two new comparable gray gifs with a simpler QWidget subclass.

SGaist

Hi,

Something just came to mind: maybe QStaticText might be of interest.

xce1

@SGaist Hi, thanks. I just tried that, It's still the same.

Christian Ehrlicher

I've no performance problem with your code on linux and windows7 (both in a VM, 64bit, Qt5.15.x)

xce1

This post is deleted!

xce1

@Christian-Ehrlicher

Hi, Thank you for your attention.

Would you please take a look at the situation below ?

@xce1 said in How can I replce Qpainter::drawText with a more effecient way to draw text in a table cell:

I've tested it with a single drawText call in paintEvent, the problem still exists.
But if I put a label on widget, the problem disappears!
main.cpp

#include <QtWidgets/QApplication>
#include "QPlainStyleTable.h"
#include "QtClass.h"

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

//     auto _m_pTable = new QPlainStyleTable();
//     _m_pTable->SetHeaderColor(Qt::red, Qt::green);
//     _m_pTable->SetContentColor(Qt::gray, Qt::yellow, Qt::blue);
//     _m_pTable->SetBorderColor(Qt::white);
//     //_m_pTable->SetFont(QFont(u8"微软雅黑"), QFont(u8"微软雅黑"));
// 
//     _m_pTable->SetDimension(1, 1);
// 
//     _m_pTable->SetTitle({ "a", "b", "c", "d", "e" });
//     _m_pTable->AddData({ "a1", "b1", "c1", "d1", "e1`" });
//     _m_pTable->AddData({ "a2", "b2", "c2", "d2", "e2" });
//     _m_pTable->AddData({ "a3", "b3", "c3", "d3", "e3" });
//     _m_pTable->AddData({ "a4", "b4", "c4", "d4", "e4" });
//     
//     _m_pTable->show();
    auto _m_pQClass = new QtClass(nullptr);
    _m_pQClass->setFixedSize(500, 400);
    _m_pQClass->show();
    return a.exec();
}

QtClass.h

#pragma once

#include <QWidget>

class QtClass : public QWidget
{
    Q_OBJECT

public:
    QtClass(QWidget *parent);
    ~QtClass();

    void paintEvent(QPaintEvent* e) override;
};

QtClass.cpp with QLabel commented out.

#include "QtClass.h"

#include <QPainter>
#include <QLabel>

QtClass::QtClass(QWidget *parent)
    : QWidget(parent)
{
//     auto _pLabel = new QLabel(this);
//     _pLabel->setText("HELLO WORLD!");
//     _pLabel->move(200, 300);
}

QtClass::~QtClass()
{
}

void QtClass::paintEvent(QPaintEvent* e)
{
    QPainter painter(this);
    painter.drawText(0, 0, 100, 200, Qt::AlignCenter | Qt::TextSingleLine | Qt::TextDontClip | Qt::TextWordWrap, QString("Hello World!"));
}

QtClass.cpp with QLabel .

#include "QtClass.h"

#include <QPainter>
#include <QLabel>

QtClass::QtClass(QWidget *parent)
    : QWidget(parent)
{
    auto _pLabel = new QLabel(this);
    _pLabel->setText("HELLO WORLD!");
    _pLabel->move(200, 300);
}

QtClass::~QtClass()
{
}

void QtClass::paintEvent(QPaintEvent* e)
{
    QPainter painter(this);
    painter.drawText(0, 0, 100, 200, Qt::AlignCenter | Qt::TextSingleLine | Qt::TextDontClip | Qt::TextWordWrap, QString("Hello World!"));
}

Christian Ehrlicher

@xce1 said in How can I replce Qpainter::drawText with a more effecient way to draw text in a table cell:

Would you please take a look at the situation below ?

That's the same code as above.

xce1

@Christian-Ehrlicher
Yes. It is. I thought maybe you missed the last post. Sorry about that.

I used Qt5.14.2 on Win10 VS2019.

Since no one else has the same problem. I'm about to just put a QLabel or other Qt widget to bypass it.

Thank you anyway.

J.Hilk

@xce1 have you tried a release build with O3 ? maybe its just a debug/development issue

xce1

@J-Hilk I just tried that. It's the same as no debug.
There is a visible blank background before "Hello World" shows up
if I didn't add a QLabel in QtClass constructor.
Thank you!