Added more code snippets

Opacity/MainWindow.cpp

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+/**
+ * This work is licensed under the Creative Commons Attribution 3.0 Unported 
+ * License. To view a copy of this license, visit 
+ * http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative 
+ * Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+ */
+
+/* StackOverflow reference:
+ * http://stackoverflow.com/questions/12307119/qgraphicssceneitems-returns-no-items-for-a-given-rect
+ */
+
+#include "MainWindow.h"
+#include "ui_MainWindow.h"
+
+#include <QDebug>
+#include <QKeyEvent>
+#include <QGraphicsPixmapItem>
+
+MainWindow::MainWindow(QWidget *parent) :
+    QMainWindow(parent),
+    ui(new Ui::MainWindow)
+  , scene(new QGraphicsScene())
+{
+    ui->setupUi(this);
+
+    ui->graphicsView->setScene(scene);
+    ui->graphicsView->installEventFilter(this);
+    ui->graphicsView->show();
+
+    for (int y = 0; y < 20; ++y) {
+        for (int x = 0; x < 20; ++x) {
+            QPixmap pixmap("desert.png");
+            QGraphicsPixmapItem* newItem(scene->addPixmap(pixmap));
+            newItem->setPos(x * 25, y * 25);
+            newItem->setOpacity(0.01);
+            qDebug() << newItem << newItem->isVisible();
+        }
+    }
+}
+
+MainWindow::~MainWindow()
+{
+    delete ui;
+    delete scene;
+}
+
+bool MainWindow::eventFilter(QObject *obj, QEvent *event)
+{
+    if(event->type() == QEvent::KeyPress) {
+        QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
+        if (keyEvent->key() == Qt::Key_Space) {
+            QRectF rect(0, 0, 25 * 3, 25 * 3);
+            QList<QGraphicsItem*> items(scene->items(rect, Qt::ContainsItemBoundingRect, Qt::AscendingOrder));
+            qDebug() << items;
+            foreach (QGraphicsItem *item, items) {
+                item->setOpacity(1.0);
+            }
+        }
+        return true;
+    }
+    return QObject::eventFilter(obj, event);
+}

Opacity/MainWindow.h

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+/**
+ * This work is licensed under the Creative Commons Attribution 3.0 Unported 
+ * License. To view a copy of this license, visit 
+ * http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative 
+ * Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+ */
+
+/* StackOverflow reference:
+ * http://stackoverflow.com/questions/12307119/qgraphicssceneitems-returns-no-items-for-a-given-rect
+ */
+
+#include <QMainWindow>
+#include <QWidget>
+#include <QEvent>
+#include <QGraphicsScene>
+#include "ui_MainWindow.h"
+
+class MainWindow : public QMainWindow {
+	Q_OBJECT
+
+public:
+
+	MainWindow(QWidget* parent);
+	~MainWindow();
+	bool eventFilter(QObject *obj, QEvent *event);
+
+        Ui_MainWindow* ui;
+        QGraphicsScene* scene;
+};

Opacity/MainWindow.ui

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+<?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>800</width>
+    <height>600</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string>MainWindow</string>
+  </property>
+  <widget class="QWidget" name="centralwidget">
+   <layout class="QVBoxLayout" name="verticalLayout">
+    <item>
+     <widget class="QGraphicsView" name="graphicsView"/>
+    </item>
+   </layout>
+  </widget>
+  <widget class="QMenuBar" name="menubar">
+   <property name="geometry">
+    <rect>
+     <x>0</x>
+     <y>0</y>
+     <width>800</width>
+     <height>23</height>
+    </rect>
+   </property>
+  </widget>
+  <widget class="QStatusBar" name="statusbar"/>
+ </widget>
+ <resources/>
+ <connections/>
+</ui>

Opacity/Opacity.pro

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+# This work is licensed under the Creative Commons Attribution 3.0 Unported
+# License. To view a copy of this license, visit
+# http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative
+# Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+
+TEMPLATE = app
+QT = gui core
+
+CONFIG += qt warn_on
+FORMS = MainWindow.ui
+HEADERS = MainWindow.h
+SOURCES = MainWindow.cpp main.cpp

Opacity/main.cpp

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+/**
+ * This work is licensed under the Creative Commons Attribution 3.0 Unported 
+ * License. To view a copy of this license, visit 
+ * http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative 
+ * Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+ */
+
+/* StackOverflow reference:
+ * http://stackoverflow.com/questions/12307119/qgraphicssceneitems-returns-no-items-for-a-given-rect
+ */
+
+#include "MainWindow.h"
+
+int main(int argc, char ** argv) {
+
+	QApplication app( argc, argv );
+
+	MainWindow win(0);
+	win.show(); 
+	app.connect( &app, SIGNAL( lastWindowClosed() ), &app, SLOT( quit() ) );
+
+	return app.exec();
+}

QDataStream/Datastream.pro

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+# This work is licensed under the Creative Commons Attribution 3.0 Unported
+# License. To view a copy of this license, visit
+# http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative
+# Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+
+TEMPLATE = app
+QT = core
+CONFIG += console qt warn_on
+SOURCES = main.cpp

QDataStream/main.cpp

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+/**
+ * This work is licensed under the Creative Commons Attribution 3.0 Unported 
+ * License. To view a copy of this license, visit 
+ * http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative 
+ * Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+ */
+
+/* StackOverflow reference:
+ * http://stackoverflow.com/questions/12501140/qt-qstring-from-qdatastream
+ */
+
+#include <QCoreApplication>
+#include <QDebug>
+#include <QDataStream>
+#include <QBuffer>
+
+void myFunc(QDataStream& in)
+{
+    quint8 v;
+    in >> v;
+qDebug() << v;
+    // Ok, I caught v value successfuly
+    QString s;
+    in >> s;
+qDebug() << s;
+    // Didnt work :<
+}
+
+
+int main(int argc, char ** argv) {
+    QCoreApplication a(argc, argv);
+
+    QBuffer buffer;
+    buffer.open(QBuffer::ReadWrite);
+
+    // write test data into the biffer
+    QDataStream out(&buffer);
+    quint8 ival = 42;
+    QString sval = "Qt";
+    out << ival;
+    out << sval;
+
+    // read back data
+    buffer.seek(0);
+    myFunc(out);
+
+
+    return a.exec();
+}

QTextEdit/MainWindow.cpp

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+/**
+ * This work is licensed under the Creative Commons Attribution 3.0 Unported 
+ * License. To view a copy of this license, visit 
+ * http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative 
+ * Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+ */
+
+/* StackOverflow reference:
+ * http://stackoverflow.com/questions/12606365/how-to-match-tab-length-to-a-number-of-spaces-in-qt
+ */
+
+#include "MainWindow.h"
+#include "ui_MainWindow.h"
+
+#include <QDebug>
+#include <QKeyEvent>
+#include <QGraphicsPixmapItem>
+
+MainWindow::MainWindow(QWidget *parent) :
+    QMainWindow(parent),
+    ui(new Ui::MainWindow) {
+
+    ui->setupUi(this);
+    ui->textEdit->setFontFamily("Courier New");
+    QFontMetrics fm(ui->textEdit->currentFont());
+    int spaceWidth = fm.width(" ");
+    int tabStop = spaceWidth * 4;
+    ui->textEdit->setTabStopWidth(tabStop + 1);
+    ui->textEdit->setText("\tAfter one tab\n"
+                          "    After 4 spaces\n"
+                          "\t\tAfter two tabs\n"
+                          "        After 8 spaces\n"
+                          "\t\t\t\t\t\tAfter six tabs\n"
+                          "                        After 24 spaces\n"
+                          "\t\t\t\t\t\t\t\t\t\t\t\tAfter 12 tabs\n"
+                          "                                                After 48 spaces\n");
+}
+
+MainWindow::~MainWindow()
+{
+    delete ui;
+}

QTextEdit/MainWindow.h

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+/**
+ * This work is licensed under the Creative Commons Attribution 3.0 Unported 
+ * License. To view a copy of this license, visit 
+ * http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative 
+ * Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+ */
+
+/* StackOverflow reference:
+ * http://stackoverflow.com/questions/12606365/how-to-match-tab-length-to-a-number-of-spaces-in-qt
+ */
+
+#include <QMainWindow>
+#include <QWidget>
+#include "ui_MainWindow.h"
+
+class MainWindow : public QMainWindow {
+	Q_OBJECT
+
+public:
+
+	MainWindow(QWidget* parent);
+	~MainWindow();
+
+        Ui_MainWindow* ui;
+};

QTextEdit/MainWindow.ui

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+<?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>800</width>
+    <height>600</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string>MainWindow</string>
+  </property>
+  <widget class="QWidget" name="centralwidget">
+   <layout class="QVBoxLayout" name="verticalLayout">
+    <item>
+     <widget class="QTextEdit" name="textEdit"/>
+    </item>
+   </layout>
+  </widget>
+  <widget class="QMenuBar" name="menubar">
+   <property name="geometry">
+    <rect>
+     <x>0</x>
+     <y>0</y>
+     <width>800</width>
+     <height>23</height>
+    </rect>
+   </property>
+  </widget>
+  <widget class="QStatusBar" name="statusbar"/>
+ </widget>
+ <resources/>
+ <connections/>
+</ui>

QTextEdit/Textedit.pro

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+# This work is licensed under the Creative Commons Attribution 3.0 Unported
+# License. To view a copy of this license, visit
+# http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative
+# Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+
+TEMPLATE = app
+QT = gui core
+CONFIG += qt warn_on
+FORMS = MainWindow.ui
+HEADERS = MainWindow.h
+SOURCES = MainWindow.cpp main.cpp

QTextEdit/main.cpp

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+/**
+ * This work is licensed under the Creative Commons Attribution 3.0 Unported 
+ * License. To view a copy of this license, visit 
+ * http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative 
+ * Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+ */
+
+/* StackOverflow reference:
+ * http://stackoverflow.com/questions/12606365/how-to-match-tab-length-to-a-number-of-spaces-in-qt
+ */
+
+#include "MainWindow.h"
+
+int main(int argc, char ** argv) {
+
+	QApplication app( argc, argv );
+
+	MainWindow win(0);
+	win.show(); 
+	app.connect( &app, SIGNAL( lastWindowClosed() ), &app, SLOT( quit() ) );
+
+	return app.exec();
+}

qmakeConflict/CMakeLists.txt

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+cmake_minimum_required (VERSION 2.6)
+project (conflict)
+add_executable(conflict foo/conflict.cpp bar/conflict.cpp main.cpp)
+include_directories("/usr/include/qt4/QtGui" "/usr/include/qt4")
+

qmakeConflict/Conflict.pro

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+# This work is licensed under the Creative Commons Attribution 3.0 Unported
+# License. To view a copy of this license, visit
+# http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative
+# Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
+
+TEMPLATE = app
+QT = gui core
+CONFIG += qt warn_on
+
+HEADERS = foo/conflict.h bar/conflict.h
+SOURCES = foo/conflict.cpp bar/conflict.cpp