WASM merge wasm-qt into static module

Change-Id: I1ed26685561fd79d26cc0844faa3dfe4c00d439a
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/128625
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

9 files changed, 1084 insertions, 0 deletions

diff --git a/static/CustomTarget_wasm-qt5-mandelbrot_moc.mk b/static/CustomTarget_wasm-qt5-mandelbrot_moc.mk
new file mode 100644
index 000000000000..d3da8235c5f9
--- /dev/null
+++ b/static/CustomTarget_wasm-qt5-mandelbrot_moc.mk
@@ -0,0 +1,37 @@
+# -*- Mode: makefile-gmake; tab-width: 4; indent-tabs-mode: t -*-
+#
+# This file is part of the LibreOffice project.
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+#
+
+$(eval $(call gb_CustomTarget_CustomTarget,static/qt5-mandelbrot))
+
+$(call gb_CustomTarget_get_target,static/qt5-mandelbrot) : \
+	$(call gb_CustomTarget_get_workdir,static/qt5-mandelbrot)/renderthread.moc \
+	$(call gb_CustomTarget_get_workdir,static/qt5-mandelbrot)/mandelbrotwidget.moc \
+
+qt5_mandelbrot_MOCDEFS_H := $(call gb_CustomTarget_get_workdir,static/qt5-mandelbrot)/moc_predefs.h
+qt5_mandelbrot_MOCDEFS_CXX := $(call gb_CustomTarget_get_workdir,static/qt5-mandelbrot)/moc_dummy.cxx
+qt5_mandelbrot_WORKDIR :=  $(call gb_CustomTarget_get_workdir,static/qt5-mandelbrot)/.dir
+
+$(qt5_mandelbrot_MOCDEFS_CXX): | $(qt5_mandelbrot_WORKDIR)
+	touch $@
+
+$(qt5_mandelbrot_MOCDEFS_H): $(qt5_mandelbrot_MOCDEFS_CXX) | $(qt5_mandelbrot_WORKDIR)
+	$(call gb_Output_announce,$(subst $(WORKDIR)/,,$@),$(true),CXX,1)
+	$(call gb_Trace_StartRange,$(subst $(WORKDIR)/,,$@),CXX)
+	$(CXX) -pipe -O2 -std=gnu++11 -fno-exceptions $(gb_EMSCRIPTEN_CPPFLAGS) -dM -E -o $@ $<
+	$(call gb_Trace_EndRange,$(subst $(WORKDIR)/,,$@),MOC)
+
+$(call gb_CustomTarget_get_workdir,static/qt5-mandelbrot)/%.moc : \
+		$(SRCDIR)/static/source/qt5-mandelbrot/%.h \
+		$(qt5_mandelbrot_MOCDEFS_H) | $(qt5_mandelbrot_WORKDIR)
+	$(call gb_Output_announce,$(subst $(WORKDIR)/,,$@),$(true),MOC,1)
+	$(call gb_Trace_StartRange,$(subst $(WORKDIR)/,,$@),MOC)
+	$(MOC5) --include $(qt5_mandelbrot_MOCDEFS_H) $(gb_EMSCRIPTEN_QTDEFS) $< -o $@
+	$(call gb_Trace_EndRange,$(subst $(WORKDIR)/,,$@),MOC)
+
+# vim: set noet sw=4:
diff --git a/static/Executable_wasm-qt5-mandelbrot.mk b/static/Executable_wasm-qt5-mandelbrot.mk
new file mode 100644
index 000000000000..e7eac989110e
--- /dev/null
+++ b/static/Executable_wasm-qt5-mandelbrot.mk
@@ -0,0 +1,32 @@
+# -*- Mode: makefile-gmake; tab-width: 4; indent-tabs-mode: t -*-
+#
+# This file is part of the LibreOffice project.
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+#
+
+$(eval $(call gb_Executable_Executable,wasm-qt5-mandelbrot))
+
+$(eval $(call gb_Executable_use_custom_headers,wasm-qt5-mandelbrot,static/qt5-mandelbrot))
+
+$(eval $(call gb_Executable_use_externals,wasm-qt5-mandelbrot,\
+    graphite \
+    freetype \
+    harfbuzz \
+    libpng \
+    qt5 \
+))
+
+$(eval $(call gb_Executable_add_exception_objects,wasm-qt5-mandelbrot,\
+    static/source/qt5-mandelbrot/main \
+    static/source/qt5-mandelbrot/mandelbrotwidget \
+    static/source/qt5-mandelbrot/renderthread \
+))
+
+$(eval $(call gb_Executable_add_defs,wasm-qt5-mandelbrot,\
+    -DVCL_INTERNALS \
+))
+
+# vim: set noet sw=4 ts=4:
diff --git a/static/Module_static.mk b/static/Module_static.mk
index 3c323d6c0e7c..a21b2355741b 100644
--- a/static/Module_static.mk
+++ b/static/Module_static.mk
@@ -18,6 +18,8 @@ $(eval $(call gb_Module_add_targets,static,\
 ifeq (EMSCRIPTEN,$(OS))
 $(eval $(call gb_Module_add_targets,static,\
     CustomTarget_emscripten_fs_image \
+    CustomTarget_wasm-qt5-mandelbrot_moc \
+    Executable_wasm-qt5-mandelbrot \
 ))
 endif
 
diff --git a/static/README.wasm.md b/static/README.wasm.md
new file mode 100644
index 000000000000..bfe930ef6775
--- /dev/null
+++ b/static/README.wasm.md
@@ -0,0 +1,299 @@
+# Support for Emscripten Cross Build
+
+This module provides support for emscripten cross build
+
+## Status
+
+    $ make
+
+You can run the WASM mandelbrot Qt example, if you copy its HTML
+and the qtloader.js from the Qt's example folder after build with:
+
+    $ emrun --serve_after_close workdir/LinkTarget/Executable/mandelbrot.html
+
+REMINDER: Always start new tabs in the browser, reload might fail / cache!
+
+
+## Setup for the LO WASM build (with Qt)
+
+We're using Qt 5.15 with the officially supported emscripten v1.39.8.
+But there are several potential problems with threads and exceptions, so this will likely
+change later to a newer emscripten.
+
+Qt WASM is not yet used with LO, just if you're wondering!
+
+- See below under Docker build for another build option
+
+### Setup emscripten
+
+<https://emscripten.org/docs/getting_started/index.html>
+
+    git clone https://github.com/emscripten-core/emsdk.git
+    ./emsdk install 1.39.8
+    ./emsdk activate --embedded 1.39.8
+
+Example `bashrc` scriptlet:
+
+    EMSDK_ENV=$HOME/Development/libreoffice/git_emsdk/emsdk_env.sh
+    [ -f "$EMSDK_ENV" ] && \. "$EMSDK_ENV" 1>/dev/null 2>&1
+
+### Setup Qt
+
+<https://doc.qt.io/qt-5/wasm.html>
+
+I originally build the Qt 5.15 branch, but probably better to build a tag like v5.15.2.
+
+So:
+
+    git clone https://github.com/qt/qt5.git
+    cd qt5
+    git checkout v5.15.2
+    ./init-repository
+    ./configure -xplatform wasm-emscripten -feature-thread -compile-examples -prefix $PWD/qtbase
+    make -j<CORES> module-qtbase module-qtdeclarative
+
+Building with examples will break with some of them, but at that point Qt already works.
+
+At some point Qt configure failed for me with:
+
+"Checking for target architecture... Project ERROR: target architecture detection binary not found."
+
+What seems to have fixed this was to run "emsdk activate 1.39.8" again.
+
+Current Qt fails to start the demo webserver: <https://bugreports.qt.io/browse/QTCREATORBUG-24072>
+
+Use `emrun --serve_after_close` to run Qt WASM demos
+
+Enabling multi-thread support in Firefox is a bit of work with older versions:
+
+- <https://bugzilla.mozilla.org/show_bug.cgi?id=1477743#c7>
+- <https://wiki.qt.io/Qt_for_WebAssembly#Multithreading_Support>
+- <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer>
+
+
+### Setup LO
+
+`autogen.sh` is patched to use emconfigure. That basically sets various environment vars,
+especially `EMMAKEN_JUST_CONFIGURE`, which will create the correct output file names, checked by
+`configure` (`a.out`).
+
+There's a distro config for WASM (work in progress), that gets your
+defaults right (and currently disables a ton of 3rd party stuff which
+is not essential).
+
+Recommended configure setup is thusly:
+
+* grab defaults
+    `--with-distro=LibreOfficeWASM32`
+
+* local config
+    `QT5DIR=/dir/of/git_qt5/qtbase`
+
+* if you want to use ccache on both sides of the build
+    `--with-build-platform-configure-options=--enable-ccache`
+    `--enable-ccache`
+
+### Using Docker to cross-build with emscripten
+
+If you prefer a controlled environment (sadly emsdk install/activate
+is _not_ stable over time, as e.g. nodejs versions evolve), that is
+easy to replicate across different machines - consider the docker
+images we're providing.
+
+Config/setup file see
+<https://git.libreoffice.org/lode/+/ccb36979563635b51215477455953252c99ec013>
+
+Run
+
+    docker-compose build
+
+in the lode/docker dir to get the container prepared. Run
+
+    PARALLELISM=4 BUILD_OPTIONS= BUILD_TARGET=build docker-compose run --rm -e PARALLELISM -e BUILD_TARGET -e BUILD_OPTIONS builder
+
+to perform an actual `srcdir != builddir` build; the container mounts
+checked-out git repo and output dir via `docker-compose.yml` (so make
+sure the path names there match your setup):
+
+The lode setup expects, inside the lode/docker subdir, the following directories:
+
+- core (`git checkout`)
+- workdir (the output dir - gets written into)
+- cache (`ccache tree`)
+- tarballs (external project tarballs gets written and cached there)
+
+
+## Ideas for an UNO bridge implementation
+
+My post to Discord #emscripten:
+
+"I'm looking for a way to do an abstract call
+from one WASM C++ object to another WASM C++ object, so like FFI / WebIDL,
+just within WASM. All my code is C++ and normally I have bridge code, with
+assembler to implement the function call /RTTI and exception semantics of the
+specified platform. Code is at
+<https://cgit.freedesktop.org/libreoffice/core/tree/bridges/source/cpp_uno>.
+I've read a bit about `call_indirect` and stuff, but I don't have yet a good
+idea, how I could implement this (and  there is an initial feature/wasm branch
+for the interested). I probably need some fixed lookup table, like on iOS,
+because AFAIK you can't dynamically generate code in WASM. So any pointers or
+ideas for an implementation? I can disassemble some minimalistic WASM example
+and read clang code for `WASM_EmscriptenInvoke`, but if there were some
+standalone code or documentation I'm missing, that would be nice to know."
+
+We basically would go the same way then the other backends. Write the bridge in
+C++, which is probably largely boilerplate code, but the function call in WAT
+(<https://github.com/WebAssembly/wabt>) based on the LLVM WASM calling
+conventions in `WASM_EmscriptenInvoke`. I didn't get a reply to that question for
+hours. Maybe I'll open an Emscripten issue, if we really have to implement
+this.
+
+WASM dynamic dispatch:
+
+- <https://fitzgeraldnick.com/2018/04/26/how-does-dynamic-dispatch-work-in-wasm.html>
+
+
+## Workaround for eventual clang WASM compiler bug
+
+````
+sc/source/core/data/attarray.cxx:378:44: error: call to member function 'erase' is ambiguous
+                        aNewCondFormatData.erase(nIndex);
+                        ~~~~~~~~~~~~~~~~~~~^~~~~
+include/o3tl/sorted_vector.hxx:86:15: note: candidate function
+    size_type erase( const Value& x )
+              ^
+include/o3tl/sorted_vector.hxx:97:10: note: candidate function
+    void erase( size_t index )
+````
+
+This is currently patched by using `x.erase` (`x.begin() + nIndex`).
+
+There shouldn't be an ambiguity, because of "[WebAssembly] Change size_t to `unsigned long`."
+<https://reviews.llvm.org/rGdf07a35912d78781ed6a62a7c032bfef5085a4f5#change-IrS9f6jH6PFq>,
+from "Jul 23 2018" which pre-dates the emscripten tag 1.39.8 from 02/14/2020 by ~1.5y.
+
+
+## Tools for problem diagnosis
+
+* `nm -s` should list the symbols in the archive, based on the index generated by ranlib.
+  If you get linking errors that archive has no index.
+
+
+## Emscripten filesystem access with threads
+
+This is closed, but not really fixed IMHO:
+
+- <https://github.com/emscripten-core/emscripten/issues/3922>
+
+
+## Dynamic libraries `/` modules in emscripten
+
+There is a good summary in:
+
+- <https://bugreports.qt.io/browse/QTBUG-63925>
+
+Summary: you can't use modules and threads.
+
+This is mentioned at the end of:
+
+- <https://github.com/emscripten-core/emscripten/wiki/Linking>
+
+The usage of `MAIN_MODULE` and `SIDE_MODULE` has other problems, a major one IMHO is symbol resolution at runtime only.
+So this works really more like plugins in the sense of symbol resolution without dependencies `/` rpath.
+
+There is some clang-level dynamic-linking in progress (WASM dlload). The following link is already a bit old,
+but I found it a god summary of problems to expect:
+
+- <https://iandouglasscott.com/2019/07/18/experimenting-with-webassembly-dynamic-linking-with-clang/>
+
+
+## Mixed information, links, problems, TODO
+
+More info on Qt WASM emscripten pthreads:
+
+- <https://wiki.qt.io/Qt_for_WebAssembly#Multithreading_Support>
+
+WASM needs `-pthread` at compile, not just link time for atomics support. Alternatively you can provide
+`-s USE_PTHREADS=1`, but both don't seem to work reliable, so best provide both.
+<https://github.com/emscripten-core/emscripten/issues/10370>
+
+The output file must have the prefix .o, otherwise the WASM files will get a
+`node.js` shebang (!) and ranlib won't be able to index the library (link errors).
+
+Qt with threads has further memory limit. From Qt configure:
+````
+Project MESSAGE: Setting PTHREAD_POOL_SIZE to 4
+Project MESSAGE: Setting TOTAL_MEMORY to 1GB
+````
+
+You can actually allocate 4GB:
+
+- <https://bugzilla.mozilla.org/show_bug.cgi?id=1392234>
+
+LO uses a nested event loop to run dialogs in general, but that won't work, because you can't drive
+the browser event loop. like VCL does with the system event loop in the various VCL backends.
+Changing this will need some major work (basically dropping Application::Execute).
+
+But with the know problems with exceptions and threads, this might change:
+
+- <https://github.com/emscripten-core/emscripten/pull/11518>
+- <https://github.com/emscripten-core/emscripten/issues/11503>
+- <https://github.com/emscripten-core/emscripten/issues/11233>
+- <https://github.com/emscripten-core/emscripten/issues/12035>
+
+We're also using emconfigure at the moment. Originally I patched emscripten, because it
+wouldn't create the correct a.out file for C++ configure tests. Later I found that
+the `emconfigure` sets `EMMAKEN_JUST_CONFIGURE` to work around the problem.
+
+ICU bug:
+
+- <https://github.com/emscripten-core/emscripten/issues/10129>
+
+Alternative, probably:
+
+- <https://developer.mozilla.org/de/docs/Web/JavaScript/Reference/Global_Objects/Intl>
+
+There is a wasm64, but that still uses 32bit pointers!
+
+Old outdated docs:
+
+- <https://wiki.documentfoundation.org/Development/Emscripten>
+
+Reverted patch:
+
+- <https://cgit.freedesktop.org/libreoffice/core/commit/?id=0e21f6619c72f1e17a7b0a52b6317810973d8a3e>
+
+Generally <https://emscripten.org/docs/porting>:
+
+- <https://emscripten.org/docs/porting/guidelines/api_limitations.html#api-limitations>
+- <https://emscripten.org/docs/porting/files/file_systems_overview.html#file-system-overview>
+- <https://emscripten.org/docs/porting/pthreads.html>
+- <https://emscripten.org/docs/porting/emscripten-runtime-environment.html>
+
+This will be interesting:
+
+- <https://emscripten.org/docs/getting_started/FAQ.html#how-do-i-run-an-event-loop>
+
+This didn't help much yet:
+
+- <https://github.com/emscripten-ports>
+
+Emscripten supports standalone WASI binaries:
+
+- <https://github.com/emscripten-core/emscripten/wiki/WebAssembly-Standalone>
+- <https://www.qt.io/qt-examples-for-webassembly>
+- <http://qtandeverything.blogspot.com/2017/06/qt-for-web-assembly.html>
+- <http://qtandeverything.blogspot.com/2020/>
+- <https://emscripten.org/docs/api_reference/Filesystem-API.html>
+- <https://discuss.python.org/t/add-a-webassembly-wasm-runtime/3957/12>
+- <http://git.savannah.gnu.org/cgit/config.git>
+- <https://webassembly.org/specs/>
+- <https://developer.chrome.com/docs/native-client/>
+- <https://emscripten.org/docs/getting_started/downloads.html>
+- <https://github.com/openpgpjs/openpgpjs/blob/master/README.md#getting-started>
+- <https://developer.mozilla.org/en-US/docs/WebAssembly/Using_the_JavaScript_API>
+- <https://github.com/bytecodealliance/wasmtime/blob/main/docs/WASI-intro.md>
+- <https://www.ip6.li/de/security/x.509_kochbuch/openssl-fuer-webassembly-compilieren>
+- <https://emscripten.org/docs/introducing_emscripten/about_emscripten.html#about-emscripten-porting-code>
+- <https://emscripten.org/docs/compiling/Building-Projects.html>
+
diff --git a/static/source/qt5-mandelbrot/main.cxx b/static/source/qt5-mandelbrot/main.cxx
new file mode 100644
index 000000000000..037c63153cf2
--- /dev/null
+++ b/static/source/qt5-mandelbrot/main.cxx
@@ -0,0 +1,66 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "mandelbrotwidget.h"
+
+#include <QtWidgets/QApplication>
+#include <QtCore/QtPlugin>
+
+Q_IMPORT_PLUGIN(QWasmIntegrationPlugin)
+
+int main(int argc, char* argv[])
+{
+    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+    QCoreApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+    QApplication app(argc, argv);
+    MandelbrotWidget widget;
+    widget.show();
+    return app.exec();
+}
diff --git a/static/source/qt5-mandelbrot/mandelbrotwidget.cxx b/static/source/qt5-mandelbrot/mandelbrotwidget.cxx
new file mode 100644
index 000000000000..5886dd2664c0
--- /dev/null
+++ b/static/source/qt5-mandelbrot/mandelbrotwidget.cxx
@@ -0,0 +1,228 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "mandelbrotwidget.h"
+#include "mandelbrotwidget.moc"
+
+#include <QtGui/QPainter>
+#include <QtGui/QKeyEvent>
+
+#include <math.h>
+
+const double DefaultCenterX = -0.637011;
+const double DefaultCenterY = -0.0395159;
+const double DefaultScale = 0.00403897;
+
+const double ZoomInFactor = 0.8;
+const double ZoomOutFactor = 1 / ZoomInFactor;
+const int ScrollStep = 20;
+
+MandelbrotWidget::MandelbrotWidget(QWidget* parent)
+    : QWidget(parent)
+    , centerX(DefaultCenterX)
+    , centerY(DefaultCenterY)
+    , pixmapScale(DefaultScale)
+    , curScale(DefaultScale)
+{
+    connect(&thread, &RenderThread::renderedImage, this, &MandelbrotWidget::updatePixmap);
+
+    setWindowTitle(tr("Mandelbrot"));
+#if QT_CONFIG(cursor)
+    setCursor(Qt::CrossCursor);
+#endif
+    resize(550, 400);
+}
+
+void MandelbrotWidget::paintEvent(QPaintEvent* /* event */)
+{
+    QPainter painter(this);
+    painter.fillRect(rect(), Qt::black);
+
+    if (pixmap.isNull())
+    {
+        painter.setPen(Qt::white);
+        painter.drawText(rect(), Qt::AlignCenter, tr("Rendering initial image, please wait..."));
+        return;
+    }
+
+    if (qFuzzyCompare(curScale, pixmapScale))
+    {
+        painter.drawPixmap(pixmapOffset, pixmap);
+    }
+    else
+    {
+        auto previewPixmap = qFuzzyCompare(pixmap.devicePixelRatioF(), qreal(1))
+                                 ? pixmap
+                                 : pixmap.scaled(pixmap.size() / pixmap.devicePixelRatioF(),
+                                                 Qt::KeepAspectRatio, Qt::SmoothTransformation);
+        double scaleFactor = pixmapScale / curScale;
+        int newWidth = int(previewPixmap.width() * scaleFactor);
+        int newHeight = int(previewPixmap.height() * scaleFactor);
+        int newX = pixmapOffset.x() + (previewPixmap.width() - newWidth) / 2;
+        int newY = pixmapOffset.y() + (previewPixmap.height() - newHeight) / 2;
+
+        painter.save();
+        painter.translate(newX, newY);
+        painter.scale(scaleFactor, scaleFactor);
+
+        QRectF exposed = painter.transform().inverted().mapRect(rect()).adjusted(-1, -1, 1, 1);
+        painter.drawPixmap(exposed, previewPixmap, exposed);
+        painter.restore();
+    }
+
+    QString text = tr("Use mouse wheel or the '+' and '-' keys to zoom. "
+                      "Press and hold left mouse button to scroll.");
+    QFontMetrics metrics = painter.fontMetrics();
+    int textWidth = metrics.horizontalAdvance(text);
+
+    painter.setPen(Qt::NoPen);
+    painter.setBrush(QColor(0, 0, 0, 127));
+    painter.drawRect((width() - textWidth) / 2 - 5, 0, textWidth + 10, metrics.lineSpacing() + 5);
+    painter.setPen(Qt::white);
+    painter.drawText((width() - textWidth) / 2, metrics.leading() + metrics.ascent(), text);
+}
+
+void MandelbrotWidget::resizeEvent(QResizeEvent* /* event */)
+{
+    thread.render(centerX, centerY, curScale, size(), devicePixelRatioF());
+}
+
+void MandelbrotWidget::keyPressEvent(QKeyEvent* event)
+{
+    switch (event->key())
+    {
+        case Qt::Key_Plus:
+            zoom(ZoomInFactor);
+            break;
+        case Qt::Key_Minus:
+            zoom(ZoomOutFactor);
+            break;
+        case Qt::Key_Left:
+            scroll(-ScrollStep, 0);
+            break;
+        case Qt::Key_Right:
+            scroll(+ScrollStep, 0);
+            break;
+        case Qt::Key_Down:
+            scroll(0, -ScrollStep);
+            break;
+        case Qt::Key_Up:
+            scroll(0, +ScrollStep);
+            break;
+        default:
+            QWidget::keyPressEvent(event);
+    }
+}
+
+#if QT_CONFIG(wheelevent)
+void MandelbrotWidget::wheelEvent(QWheelEvent* event)
+{
+    const int numDegrees = event->angleDelta().y() / 8;
+    const double numSteps = numDegrees / double(15);
+    zoom(pow(ZoomInFactor, numSteps));
+}
+#endif
+
+void MandelbrotWidget::mousePressEvent(QMouseEvent* event)
+{
+    if (event->button() == Qt::LeftButton)
+        lastDragPos = event->pos();
+}
+
+void MandelbrotWidget::mouseMoveEvent(QMouseEvent* event)
+{
+    if (event->buttons() & Qt::LeftButton)
+    {
+        pixmapOffset += event->pos() - lastDragPos;
+        lastDragPos = event->pos();
+        update();
+    }
+}
+
+void MandelbrotWidget::mouseReleaseEvent(QMouseEvent* event)
+{
+    if (event->button() == Qt::LeftButton)
+    {
+        pixmapOffset += event->pos() - lastDragPos;
+        lastDragPos = QPoint();
+
+        const auto pixmapSize = pixmap.size() / pixmap.devicePixelRatioF();
+        int deltaX = (width() - pixmapSize.width()) / 2 - pixmapOffset.x();
+        int deltaY = (height() - pixmapSize.height()) / 2 - pixmapOffset.y();
+        scroll(deltaX, deltaY);
+    }
+}
+
+void MandelbrotWidget::updatePixmap(const QImage& image, double scaleFactor)
+{
+    if (!lastDragPos.isNull())
+        return;
+
+    pixmap = QPixmap::fromImage(image);
+    pixmapOffset = QPoint();
+    lastDragPos = QPoint();
+    pixmapScale = scaleFactor;
+    update();
+}
+
+void MandelbrotWidget::zoom(double zoomFactor)
+{
+    curScale *= zoomFactor;
+    update();
+    thread.render(centerX, centerY, curScale, size(), devicePixelRatioF());
+}
+
+void MandelbrotWidget::scroll(int deltaX, int deltaY)
+{
+    centerX += deltaX * curScale;
+    centerY += deltaY * curScale;
+    update();
+    thread.render(centerX, centerY, curScale, size(), devicePixelRatioF());
+}
diff --git a/static/source/qt5-mandelbrot/mandelbrotwidget.h b/static/source/qt5-mandelbrot/mandelbrotwidget.h
new file mode 100644
index 000000000000..72e95568b522
--- /dev/null
+++ b/static/source/qt5-mandelbrot/mandelbrotwidget.h
@@ -0,0 +1,91 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#pragma once
+
+#include <QtGui/QPixmap>
+#include <QtWidgets/QWidget>
+
+#include "renderthread.h"
+
+class MandelbrotWidget : public QWidget
+{
+    Q_OBJECT
+
+public:
+    MandelbrotWidget(QWidget* parent = nullptr);
+
+protected:
+    void paintEvent(QPaintEvent* event) override;
+    void resizeEvent(QResizeEvent* event) override;
+    void keyPressEvent(QKeyEvent* event) override;
+#if QT_CONFIG(wheelevent)
+    void wheelEvent(QWheelEvent* event) override;
+#endif
+    void mousePressEvent(QMouseEvent* event) override;
+    void mouseMoveEvent(QMouseEvent* event) override;
+    void mouseReleaseEvent(QMouseEvent* event) override;
+
+private slots:
+    void updatePixmap(const QImage& image, double scaleFactor);
+    void zoom(double zoomFactor);
+
+private:
+    void scroll(int deltaX, int deltaY);
+
+    RenderThread thread;
+    QPixmap pixmap;
+    QPoint pixmapOffset;
+    QPoint lastDragPos;
+    double centerX;
+    double centerY;
+    double pixmapScale;
+    double curScale;
+};
diff --git a/static/source/qt5-mandelbrot/renderthread.cxx b/static/source/qt5-mandelbrot/renderthread.cxx
new file mode 100644
index 000000000000..398e43ded15d
--- /dev/null
+++ b/static/source/qt5-mandelbrot/renderthread.cxx
@@ -0,0 +1,232 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "renderthread.h"
+#include "renderthread.moc"
+
+#include <QtGui/QImage>
+#include <cmath>
+
+RenderThread::RenderThread(QObject* parent)
+    : QThread(parent)
+{
+    for (int i = 0; i < ColormapSize; ++i)
+        m_colormap[i] = rgbFromWaveLength(380.0 + (i * 400.0 / ColormapSize));
+}
+
+RenderThread::~RenderThread()
+{
+    m_mutex.lock();
+    m_abort = true;
+    m_condition.wakeOne();
+    m_mutex.unlock();
+
+    wait();
+}
+
+void RenderThread::render(double centerX, double centerY, double scaleFactor, QSize resultSize,
+                          double devicePixelRatio)
+{
+    QMutexLocker locker(&m_mutex);
+
+    m_centerX = centerX;
+    m_centerY = centerY;
+    m_scaleFactor = scaleFactor;
+    m_devicePixelRatio = devicePixelRatio;
+    m_resultSize = resultSize;
+
+    if (!isRunning())
+    {
+        start(LowPriority);
+    }
+    else
+    {
+        m_restart = true;
+        m_condition.wakeOne();
+    }
+}
+
+void RenderThread::run()
+{
+    forever
+    {
+        m_mutex.lock();
+        const double devicePixelRatio = m_devicePixelRatio;
+        const QSize resultSize = m_resultSize * devicePixelRatio;
+        const double requestedScaleFactor = m_scaleFactor;
+        const double scaleFactor = requestedScaleFactor / devicePixelRatio;
+        const double centerX = m_centerX;
+        const double centerY = m_centerY;
+        m_mutex.unlock();
+
+        int halfWidth = resultSize.width() / 2;
+        int halfHeight = resultSize.height() / 2;
+        QImage image(resultSize, QImage::Format_RGB32);
+        image.setDevicePixelRatio(devicePixelRatio);
+
+        const int NumPasses = 8;
+        int pass = 0;
+        while (pass < NumPasses)
+        {
+            const int MaxIterations = (1 << (2 * pass + 6)) + 32;
+            const int Limit = 4;
+            bool allBlack = true;
+
+            for (int y = -halfHeight; y < halfHeight; ++y)
+            {
+                if (m_restart)
+                    break;
+                if (m_abort)
+                    return;
+
+                auto scanLine = reinterpret_cast<uint*>(image.scanLine(y + halfHeight));
+                const double ay = centerY + (y * scaleFactor);
+
+                for (int x = -halfWidth; x < halfWidth; ++x)
+                {
+                    const double ax = centerX + (x * scaleFactor);
+                    double a1 = ax;
+                    double b1 = ay;
+                    int numIterations = 0;
+
+                    do
+                    {
+                        ++numIterations;
+                        const double a2 = (a1 * a1) - (b1 * b1) + ax;
+                        const double b2 = (2 * a1 * b1) + ay;
+                        if ((a2 * a2) + (b2 * b2) > Limit)
+                            break;
+
+                        ++numIterations;
+                        a1 = (a2 * a2) - (b2 * b2) + ax;
+                        b1 = (2 * a2 * b2) + ay;
+                        if ((a1 * a1) + (b1 * b1) > Limit)
+                            break;
+                    } while (numIterations < MaxIterations);
+
+                    if (numIterations < MaxIterations)
+                    {
+                        *scanLine++ = m_colormap[numIterations % ColormapSize];
+                        allBlack = false;
+                    }
+                    else
+                    {
+                        *scanLine++ = qRgb(0, 0, 0);
+                    }
+                }
+            }
+
+            if (allBlack && pass == 0)
+            {
+                pass = 4;
+            }
+            else
+            {
+                if (!m_restart)
+                    emit renderedImage(image, requestedScaleFactor);
+                ++pass;
+            }
+        }
+
+        m_mutex.lock();
+        if (!m_restart)
+            m_condition.wait(&m_mutex);
+        m_restart = false;
+        m_mutex.unlock();
+    }
+}
+
+uint RenderThread::rgbFromWaveLength(double wave)
+{
+    double r = 0;
+    double g = 0;
+    double b = 0;
+
+    if (wave >= 380.0 && wave <= 440.0)
+    {
+        r = -1.0 * (wave - 440.0) / (440.0 - 380.0);
+        b = 1.0;
+    }
+    else if (wave >= 440.0 && wave <= 490.0)
+    {
+        g = (wave - 440.0) / (490.0 - 440.0);
+        b = 1.0;
+    }
+    else if (wave >= 490.0 && wave <= 510.0)
+    {
+        g = 1.0;
+        b = -1.0 * (wave - 510.0) / (510.0 - 490.0);
+    }
+    else if (wave >= 510.0 && wave <= 580.0)
+    {
+        r = (wave - 510.0) / (580.0 - 510.0);
+        g = 1.0;
+    }
+    else if (wave >= 580.0 && wave <= 645.0)
+    {
+        r = 1.0;
+        g = -1.0 * (wave - 645.0) / (645.0 - 580.0);
+    }
+    else if (wave >= 645.0 && wave <= 780.0)
+    {
+        r = 1.0;
+    }
+
+    double s = 1.0;
+    if (wave > 700.0)
+        s = 0.3 + 0.7 * (780.0 - wave) / (780.0 - 700.0);
+    else if (wave < 420.0)
+        s = 0.3 + 0.7 * (wave - 380.0) / (420.0 - 380.0);
+
+    r = std::pow(r * s, 0.8);
+    g = std::pow(g * s, 0.8);
+    b = std::pow(b * s, 0.8);
+    return qRgb(int(r * 255), int(g * 255), int(b * 255));
+}
diff --git a/static/source/qt5-mandelbrot/renderthread.h b/static/source/qt5-mandelbrot/renderthread.h
new file mode 100644
index 000000000000..16c0d86fd46c
--- /dev/null
+++ b/static/source/qt5-mandelbrot/renderthread.h
@@ -0,0 +1,97 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#pragma once
+
+#include <QtCore/QMutex>
+#include <QtCore/QSize>
+#include <QtCore/QThread>
+#include <QtCore/QWaitCondition>
+
+QT_BEGIN_NAMESPACE
+class QImage;
+QT_END_NAMESPACE
+
+class RenderThread : public QThread
+{
+    Q_OBJECT
+
+public:
+    RenderThread(QObject* parent = nullptr);
+    ~RenderThread();
+
+    void render(double centerX, double centerY, double scaleFactor, QSize resultSize,
+                double devicePixelRatio);
+
+signals:
+    void renderedImage(const QImage& image, double scaleFactor);
+
+protected:
+    void run() override;
+
+private:
+    static uint rgbFromWaveLength(double wave);
+
+    QMutex m_mutex;
+    QWaitCondition m_condition;
+    double m_centerX;
+    double m_centerY;
+    double m_scaleFactor;
+    double m_devicePixelRatio;
+    QSize m_resultSize;
+    bool m_restart = false;
+    bool m_abort = false;
+
+    enum
+    {
+        ColormapSize = 512
+    };
+    uint m_colormap[ColormapSize];
+};