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Thread: How to draw smootly?

  1. #1
    Join Date
    Feb 2014
    Posts
    6
    Qt products
    Qt5
    Platforms
    Unix/X11 Windows

    Default How to draw smootly?

    this code redraw two rectangles, every 10ms.
    its looks ugly.
    ezgif-2422137665.gif
    maybe need use some interpolation? if need, how to?

    All project in attached file
    TestQPainterSlowdrawing.zip


    maybe have better solution for fast drawing?


    mainwindow.cpp

    Qt Code:
    1. #include "mainwindow.h"
    2. #include "ui_mainwindow.h"
    3. #include "qaudiolevel.h"
    4. #include <QThread>
    5. #include <QDebug>
    6.  
    7. QList<QAudioLevel*> audioLevels;
    8.  
    9. MainWindow::MainWindow(QWidget *parent) :
    10. QMainWindow(parent),
    11. ui(new Ui::MainWindow)
    12. {
    13. ui->setupUi(this);
    14. ui->levelsLayout->setSpacing(0);
    15.  
    16. for(int i=0;i<2;i++)
    17. {
    18. QAudioLevel *level = new QAudioLevel(ui->centralWidget);
    19. audioLevels.append(level);
    20. ui->levelsLayout->addWidget(level);
    21. }
    22. trs = new Threadl();
    23. connect(trs,SIGNAL(SetLevels()),this,SLOT(SetLevels()));
    24. trs->start();
    25.  
    26. }
    27.  
    28. MainWindow::~MainWindow()
    29. {
    30. delete ui;
    31. }
    32.  
    33. void MainWindow::SetLevels()
    34. {
    35. float val1=((0.26-0.21)*((float)rand()/RAND_MAX))+0.21;
    36. float val2=((0.26-0.21)*((float)rand()/RAND_MAX))+0.21;
    37. qDebug() << val1 << val2;
    38. audioLevels.at(0)->setLevel(val1);
    39. audioLevels.at(1)->setLevel(val2);
    40. }
    41.  
    42. void Threadl::run()
    43. {
    44. while(true)
    45. {
    46. emit SetLevels();
    47. QThread::msleep(10);
    48. }
    49. }
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    qpainter.cpp
    Qt Code:
    1. #include "qaudiolevel.h"
    2. #include <QPainter>
    3. #include <QDebug>
    4.  
    5. QAudioLevel::QAudioLevel(QWidget *parent)
    6. : QWidget(parent)
    7. , m_level(0.0)
    8. {
    9. setMinimumHeight(15);
    10. setMaximumHeight(180);
    11. }
    12.  
    13. void QAudioLevel::setLevel(qreal level)
    14. {
    15. if (m_level != level) {
    16. m_level = level;
    17. update();
    18. }
    19. }
    20.  
    21. void QAudioLevel::paintEvent(QPaintEvent *event)
    22. {
    23. Q_UNUSED(event);
    24.  
    25. QPainter painter(this);
    26. qreal widthLevel = m_level * height();
    27. painter.fillRect(0,0, width(),height(), Qt::black);
    28. painter.fillRect(0,height()-widthLevel,50, height(), Qt::red);
    29.  
    30.  
    31.  
    32.  
    33. }
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  2. #2
    Join Date
    Jan 2006
    Location
    Graz, Austria
    Posts
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    Thanks
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    Thanked 1,545 Times in 1,495 Posts
    Qt products
    Qt3 Qt4 Qt5
    Platforms
    Unix/X11 Windows

    Default Re: How to draw smootly?

    Maybe you should describe what you want to achieve, that looks like it does what the code says it should do.

    What you can do in any case is to set the Qt::WA_NoSystemBackground widget attribute. You are filling all pixels, having Qt fill the background before calling paintEvent() is just a waste of CPU time.

    Btw, what do you need the thread for? Anything particular you are planning to add to it?

    Cheers,
    _

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