Add ::peekEventQueue() API. (#1) (#1)

Patch Qt5.6.1 for Maya. qtc-wip-add-peekeventqueue-api.patch.

From 785ec3bacfd4bf2c4b36ad21819816aea1345874 Mon Sep 17 00:00:00 2001
From: Gatis Paeglis <gatis.paeglis@theqtcompany.com>
Date: Mon, 27 Jul 2015 15:31:30 +0200
Subject: [PATCH] Add ::peekEventQueue() API

[ChangeLog][QX11Info] New API to peek into the XCB
event queue ::peekEventQueue(). This enables porting
certain Qt4 based applications to Qt5 - applications
that use Xlib's event handling functions to directly
access the X11 even queue.

We set XCB to be the owner of the X11 event queue with:

XSetEventQueueOwner(dpy, XCBOwnsEventQueue);

Which means that only XCB event handling functions
can be used to read events from the X server.

For filtering out unwanted native events Qt5 provides
QAbstractNativeEventFilter::nativeEventFilter(), but
there isn't any API in Qt to just *peek* into the queue
while the GUI thread is busy processing a long task. The
peekEventQueue() function adds this behavior to QX11Info.

Manual test included.

Task-number: QTBUG-50358
Change-Id: Id31f797f7ff76d011ad7a55a9b6c13756aaaca60

src/x11extras/doc/qtx11extras.qdocconf

@@ -22,7 +22,7 @@ qhp.QtX11Extras.subprojects.classes.indexTitle = Qt X11 Extras C++ Classes
 qhp.QtX11Extras.subprojects.classes.selectors = class fake:headerfile
 qhp.QtX11Extras.subprojects.classes.sortPages = true
 
-depends += qtcore qtwidgets qtdoc qmake
+depends += qtcore qtwidgets qtdoc qmake qtplatformheaders
 
 headerdirs  += ..
 

src/x11extras/qx11info_x11.cpp

@@ -395,4 +395,36 @@ bool QX11Info::isCompositingManagerRunning(int screen)
     return native->nativeResourceForScreen(QByteArray("compositingEnabled"), scr);
 }
 
+/*!
+    This function can be used to peek into the XCB event queue.
+
+    You can call peekEventQueue() periodically when your program is busy performing
+    a long operation (for example, copying a file or performing a long-running
+    paint operation) to check if some other action should be performed instead.
+
+    The \a peeker object needs to implement the QXcbAbstractEventPeeker interface.
+    The \a option is an enum that alters the default behavior of peekEventQueue(),
+    see QXcbAbstractEventPeeker::PeekOption.
+
+    \since 5.7
+*/
+
+void QX11Info::peekEventQueue(QXcbAbstractEventPeeker *peeker, QXcbAbstractEventPeeker::PeekOption option)
+{
+    if (!peeker || !qApp)
+        return;
+    QPlatformNativeInterface *native = qApp->platformNativeInterface();
+    if (!native)
+        return;
+
+    typedef void (*PeekEventQueueFunc)(QXcbAbstractEventPeeker *peeker, QXcbAbstractEventPeeker::PeekOption option);
+    PeekEventQueueFunc func = reinterpret_cast<PeekEventQueueFunc>(native->nativeResourceFunctionForIntegration("peekeventqueue"));
+    if (!func) {
+        qWarning("Internal error: QPA plugin doesn't implement peekEventQueue");
+        return;
+    }
+
+    func(peeker, option);
+}
+
 QT_END_NAMESPACE

src/x11extras/qx11info_x11.h

@@ -35,6 +35,8 @@
 #define QX11INFO_X11_H
 
 #include <QtCore/qnamespace.h>
+#include <QtPlatformHeaders/qxcbabstracteventpeeker.h>
+
 #include "QtX11Extras/qtx11extrasglobal.h"
 
 typedef struct _XDisplay Display;
@@ -68,6 +70,8 @@ class Q_X11EXTRAS_EXPORT QX11Info
     static xcb_connection_t *connection();
 
     static bool isCompositingManagerRunning(int screen = -1);
+    static void peekEventQueue(QXcbAbstractEventPeeker *peeker,
+                               QXcbAbstractEventPeeker::PeekOption option = QXcbAbstractEventPeeker::PeekDefault);
 
 private:
     QX11Info();

tests/manual/manual.pro

@@ -0,0 +1,3 @@
+TEMPLATE = subdirs
+
+SUBDIRS = peeker

tests/manual/peeker/main.cpp

@@ -0,0 +1,111 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#include <QtCore/QPoint>
+#include <QtCore/QRect>
+#include <QtCore/QThread>
+#include <QtGui/QPixmap>
+#include <QtGui/QPainter>
+#include <QtGui/QRegion>
+#include <QtGui/QBackingStore>
+#include <QtWidgets/QVBoxLayout>
+#include <QtWidgets/QWidget>
+#include <QtWidgets/QApplication>
+
+#include <qx11info_x11.h>
+
+class HeavyPainter : public QWidget, public QXcbAbstractEventPeeker
+{
+    Q_OBJECT
+public:
+    HeavyPainter() : m_stopTasks(false) {}
+
+    void setStopTasks(bool stop) { m_stopTasks = stop; }
+
+protected:
+    void paintEvent(QPaintEvent* e)
+    {
+        Q_UNUSED(e)
+        m_buffer = QPixmap(width(), height());
+        QPainter p(&m_buffer);
+
+        for (int i = 0; !m_stopTasks; ++i)
+        {
+            // long operation
+            p.fillRect(QRect(0, 0, width(), height()), i & 1 ? Qt::green : Qt::gray);
+            p.drawText(QPoint(10,10), "Press any key to exit");
+            QPainter p(this);
+            QPoint point = mapTo(window(), QPoint(0,0));
+            QRegion region(point.x(), point.y(), width(), height());
+
+            QBackingStore *bs = backingStore();
+            bs->beginPaint(region);
+            p.drawPixmap(0,0, m_buffer);
+
+            bs->endPaint();
+            bs->flush(region, windowHandle());
+
+            QThread::msleep(300);
+            QX11Info::peekEventQueue(this);
+        }
+
+        exit(0);
+    }
+
+    bool peekEventQueue(xcb_generic_event_t *event)
+    {
+        uint responseType = event->response_type & ~0x80;
+        if (responseType == XCB_KEY_PRESS) {
+            setStopTasks(true);
+            return true;
+        }
+
+        return false;
+    }
+
+private:
+    bool m_stopTasks;
+    QPixmap m_buffer;
+};
+
+int main(int argc, char** argv)
+{
+  QApplication app(argc, argv);
+
+  QWidget win;
+  win.setLayout(new QVBoxLayout);
+
+  QWidget *painter = new HeavyPainter;
+  win.layout()->addWidget(painter);
+
+  win.setGeometry(100,100,300,300);
+  win.show();
+
+  return app.exec();
+}
+
+#include "main.moc"

tests/manual/peeker/peeker.pro

@@ -0,0 +1,8 @@
+QT += core gui widgets x11extras
+
+LIBS += -lxcb
+
+TARGET = peeker
+TEMPLATE = app
+
+SOURCES += main.cpp

tests/tests.pro

@@ -1,5 +1,5 @@
 TEMPLATE = subdirs
 
 contains(QT_CONFIG, xcb) {
-  SUBDIRS += auto
+  SUBDIRS += auto manual
 }