add WindowPreview widget

.gitignore

@@ -13,4 +13,4 @@
 *.a
 
 build/
-*.pro.user
+*.pro.user*

dde-dock/Widgets/windowpreview.cpp

@@ -0,0 +1,81 @@
+#include <QImage>
+#include <QApplication>
+#include <QtX11Extras/QX11Info>
+#include <QPaintEvent>
+#include <QPainter>
+#include <QTimer>
+#include <QDebug>
+
+#include <X11/Xlib.h>
+#include <X11/Xutil.h>
+
+#include "windowpreview.h"
+
+WindowPreview::WindowPreview(WId sourceWindow, QWidget *parent)
+    : QWidget(parent),
+      m_sourceWindow(sourceWindow),
+      m_cache(NULL),
+      m_timer(new QTimer(this))
+{
+    m_timer->setInterval(500);
+    m_timer->setSingleShot(false);
+    m_timer->start();
+    connect(m_timer, &QTimer::timeout, [=]{ this->updateCache(); this->repaint(); });
+}
+
+WindowPreview::~WindowPreview()
+{
+    clearCache();
+}
+
+void WindowPreview::paintEvent(QPaintEvent * event)
+{
+    if (m_cache) {
+        QPainter painter(this);
+
+        QRect rect = m_cache->rect();
+        rect.moveCenter(event->rect().center());
+
+        painter.drawImage(rect, *m_cache);
+        painter.end();
+    }
+}
+
+void WindowPreview::clearCache()
+{
+    if (m_cache) {
+        delete m_cache;
+        m_cache = NULL;
+    }
+}
+
+void WindowPreview::updateCache()
+{
+    clearCache();
+
+    Display *dpy = QX11Info::display();
+
+    XWindowAttributes watts;
+    Status status = XGetWindowAttributes(dpy, m_sourceWindow, &watts);
+
+    if (status != 0) {
+        XImage *image = XGetImage(dpy, m_sourceWindow,
+                                  watts.x, watts.y, watts.width, watts.height,
+                                  AllPlanes, ZPixmap);
+        if (image) {
+            QImage cache(watts.width, watts.height, QImage::Format_RGB32);
+
+            for (int y = 0; y < watts.height; y++) {
+                for (int x = 0; x < watts.width; x++) {
+                    u_long pixel = XGetPixel(image, x, y);
+
+                    cache.setPixel(x, y, pixel);
+                }
+            }
+
+            cache = cache.scaledToWidth(width(), Qt::SmoothTransformation);
+
+            m_cache = new QImage(cache);
+        }
+    }
+}

dde-dock/Widgets/windowpreview.h

@@ -0,0 +1,30 @@
+#ifndef WINDOWPREVIEW_H
+#define WINDOWPREVIEW_H
+
+#include <QWidget>
+#include <QWindow>
+
+class QImage;
+class QTimer;
+
+class WindowPreview : public QWidget
+{
+    Q_OBJECT
+
+public:
+    WindowPreview(WId sourceWindow, QWidget *parent = 0);
+    ~WindowPreview();
+
+protected:
+    void paintEvent(QPaintEvent * event) Q_DECL_OVERRIDE;
+
+private:
+    WId m_sourceWindow;
+    QImage *m_cache;
+    QTimer *m_timer;
+
+    void clearCache();
+    void updateCache();
+};
+
+#endif // WINDOWPREVIEW_H

dde-dock/dde-dock.pro

@@ -4,7 +4,7 @@
 #
 #-------------------------------------------------
 
-QT       += core gui
+QT       += core gui x11extras
 
 greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
 
@@ -22,7 +22,8 @@ SOURCES += main.cpp\
     Widgets/dockview.cpp \
     Widgets/dockitemdelegate.cpp \
     Widgets/appitem.cpp \
-    Widgets/docklayout.cpp
+    Widgets/docklayout.cpp \
+    Widgets/windowpreview.cpp
 
 HEADERS  += mainwidget.h \
     Panel/panel.h \
@@ -33,10 +34,11 @@ HEADERS  += mainwidget.h \
     Widgets/dockview.h \
     Widgets/dockitemdelegate.h \
     Widgets/appitem.h \
-    Widgets/docklayout.h
+    Widgets/docklayout.h \
+    Widgets/windowpreview.h
 
 RESOURCES += \
     images.qrc
 
-PKGCONFIG += gtk+-2.0
+PKGCONFIG += gtk+-2.0 x11
 CONFIG += c++11 link_pkgconfig