I'm working on a drum computer application and use QGraphicsView/Scene to draw all
items. One of the main responsibilities are: By pressing of pads the ability to make
a beat (let say on a android pad or on a PC by mouse clicking).

For example folowing beat:
@
Basedrum: X.......X.X.....
Snaredrum: ....X.......X...
@

Since Qt5.3 it's no more posible to do this because of some delays (on Win7, Ubuntu 14..., Android 4....).

I made a test with a minimal implementation, additionaly test it with QWidget Button too.

I execute the app and try click fast as i can:

Timings on Qt 5.3.1 --> shortest response time ~190ms

Time: 48,593 -- Scene::mousePressEvent
Time: 48,785 -- Scene::mousePressEvent
Time: 48,985 -- Scene::mousePressEvent
Time: 49,169 -- Scene::mousePressEvent
Time: 49,361 -- Scene::mousePressEvent
Time: 35,544 -- MainWindow::on_pushButton_pressed
Time: 35,648 -- MainWindow::on_pushButton_pressed
Time: 35,752 -- MainWindow::on_pushButton_pressed
Time: 35,856 -- MainWindow::on_pushButton_pressed
Time: 35,936 -- MainWindow::on_pushButton_pressed

Timings on Qt 5.2.1 --> shortest response time ~90ms:
Time: 20,626 -- Scene::mousePressEvent
Time: 20,714 -- Scene::mousePressEvent
Time: 20,802 -- Scene::mousePressEvent
Time: 20,897 -- Scene::mousePressEvent
Time: 20,985 -- Scene::mousePressEvent
Time: 05,537 -- MainWindow::on_pushButton_pressed
Time: 05,633 -- MainWindow::on_pushButton_pressed
Time: 05,721 -- MainWindow::on_pushButton_pressed
Time: 05,825 -- MainWindow::on_pushButton_pressed
Time: 05,913 -- MainWindow::on_pushButton_pressed

@main.cpp

#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[]) {
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>

namespace Ui { class MainWindow; }
class MainWindow : public QMainWindow {
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_pushButton_pressed();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QTime>
#include <iostream>
#include <iomanip>

void debug(const QString& cName, const QString& fName) {
QTime time = QTime::currentTime();
std::cout << "Time: "
<< std::setw(2)<< std::right << std::setfill('0') << time.second()
<< ","
<< std::setw(3)<< std::left << time.msec()
<< " -- " << cName.toStdString()
<< "::" << fName.toStdString() << std::endl;
}
class Scene : public QGraphicsScene {
protected:
virtual void mousePressEvent(QGraphicsSceneMouseEvent* mouseEvent) {
Q_UNUSED(mouseEvent);
debug("Scene", "mousePressEvent");
}
};
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow) {
ui->setupUi(this);
auto rect = ui->graphicsView->geometry();
rect.adjust(0, 0, -4, -4);
ui->graphicsView->setSceneRect(rect);
ui->graphicsView->setScene(new Scene());
}
MainWindow::~MainWindow() {
delete ui;
}
void MainWindow::on_pushButton_pressed() {
debug("MainWindow", "on_pushButton_pressed");
}

mainwindow.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>196</width>
<height>96</height>
</rect>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<widget class="QWidget" name="centralWidget">
<widget class="QPushButton" name="pushButton">
<property name="geometry">
<rect>
<x>10</x>
<y>10</y>
<width>75</width>
<height>71</height>
</rect>
</property>
<property name="text">
<string>PushButton</string>
</property>
</widget>
<widget class="QGraphicsView" name="graphicsView">
<property name="geometry">
<rect>
<x>110</x>
<y>10</y>
<width>71</width>
<height>71</height>
</rect>
</property>
</widget>
</widget>
</widget>
<layoutdefault spacing="6" margin="11"/>
<resources/>
<connections/>
</ui>

TestQTGUIStuff.pro

QT += core gui
TARGET = TestQTGUIStuff
TEMPLATE = app
CONFIG += c++11
SOURCES += main.cpp
mainwindow.cpp
HEADERS += mainwindow.h
FORMS += mainwindow.ui

@

Is there something which i forgot to set up or do not correctly program?
What changes with Qt5.3 that this behaviour happens?

Thank you in advance!