diff --git a/source/backend/native/distrho/DistrhoPluginCarla.cpp b/source/backend/native/distrho/DistrhoPluginCarla.cpp
index f730f6db6..10aa562d0 100644
--- a/source/backend/native/distrho/DistrhoPluginCarla.cpp
+++ b/source/backend/native/distrho/DistrhoPluginCarla.cpp
@@ -45,10 +45,20 @@ public:
         : QMainWindow(nullptr),
           kHost(host),
           kPlugin(plugin),
+#ifdef DISTRHO_UI_OPENGL
           fWidget(this),
           fUi(this, (intptr_t)fWidget.winId(), editParameterCallback, setParameterCallback, setStateCallback, sendNoteCallback, uiResizeCallback)
+#else
+          fUi(this, 0, editParameterCallback, setParameterCallback, setStateCallback, sendNoteCallback, uiResizeCallback)
+#endif
     {
+#ifdef DISTRHO_UI_OPENGL
         setCentralWidget(&fWidget);
+#else
+        QtUI* const qtUi(fUi.getQtUI());
+        qtUi->setParent(this);
+        setCentralWidget(qtUi);
+#endif
         setWindowTitle(QString("%1 (GUI)").arg(fUi.name()));
 
         uiResize(fUi.width(), fUi.height());
@@ -123,8 +133,15 @@ protected:
 
     void uiResize(unsigned int width, unsigned int height)
     {
+#ifdef DISTRHO_UI_OPENGL
         fWidget.setFixedSize(width, height);
         setFixedSize(width, height);
+#else
+        if (fUi.resizable())
+            resize(width, height);
+        else
+            setFixedSize(width, height);
+#endif
     }
 
     // ---------------------------------------------
@@ -144,8 +161,10 @@ private:
     const HostDescriptor* const kHost;
     PluginInternal* const kPlugin;
 
-    // Qt4 stuff
+#ifdef DISTRHO_UI_OPENGL
+    // Qt stuff, used for GL
     QWidget fWidget;
+#endif
 
     // UI
     UIInternal fUi;
diff --git a/source/backend/native/notes/DistrhoPluginInfo.h b/source/backend/native/notes/DistrhoPluginInfo.h
index 0574c6990..0e76bb93e 100644
--- a/source/backend/native/notes/DistrhoPluginInfo.h
+++ b/source/backend/native/notes/DistrhoPluginInfo.h
@@ -32,6 +32,6 @@
 
 #define DISTRHO_PLUGIN_URI "http://distrho.sf.net/plugins/Notes"
 
-#define DISTRHO_UI_QT4
+#define DISTRHO_UI_QT
 
 #endif // __DISTRHO_PLUGIN_INFO_H__
diff --git a/source/backend/native/notes/DistrhoUINotes.cpp b/source/backend/native/notes/DistrhoUINotes.cpp
index 346fffd97..98f806292 100644
--- a/source/backend/native/notes/DistrhoUINotes.cpp
+++ b/source/backend/native/notes/DistrhoUINotes.cpp
@@ -26,7 +26,7 @@ START_NAMESPACE_DISTRHO
 // -------------------------------------------------
 
 DistrhoUINotes::DistrhoUINotes()
-    : Qt4UI(),
+    : QtUI(),
       fCurPage(1),
       fSaveSizeNowChecker(-1),
       fSaveTextNowChecker(-1),
@@ -61,7 +61,7 @@ DistrhoUINotes::DistrhoUINotes()
     connect(&fProgressBar, SIGNAL(valueChangedFromBar(float)), SLOT(progressBarValueChanged(float)));
     connect(&fTextEdit, SIGNAL(textChanged()), SLOT(textChanged()));
 
-    setFixedSize(300, 200);
+    setSize(300, 200);
 }
 
 DistrhoUINotes::~DistrhoUINotes()
@@ -166,14 +166,12 @@ void DistrhoUINotes::d_uiIdle()
 
     if (fSaveTextNowChecker >= 0)
         fSaveTextNowChecker++;
-
-    Qt4UI::d_uiIdle();
 }
 
 void DistrhoUINotes::resizeEvent(QResizeEvent* event)
 {
     fSaveSizeNowChecker = 0;
-    QWidget::resizeEvent(event);
+    QtUI::resizeEvent(event);
 }
 
 // -------------------------------------------------
diff --git a/source/backend/native/notes/DistrhoUINotes.hpp b/source/backend/native/notes/DistrhoUINotes.hpp
index c8df4b839..7298f4f64 100644
--- a/source/backend/native/notes/DistrhoUINotes.hpp
+++ b/source/backend/native/notes/DistrhoUINotes.hpp
@@ -18,7 +18,7 @@
 #ifndef __DISTRHO_UI_NOTES_HPP__
 #define __DISTRHO_UI_NOTES_HPP__
 
-#include "DistrhoUIQt4.hpp"
+#include "DistrhoUIQt.hpp"
 #include "paramspinbox.hpp"
 
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 0, 0))
@@ -40,7 +40,7 @@ START_NAMESPACE_DISTRHO
 
 // -------------------------------------------------
 
-class DistrhoUINotes : public Qt4UI
+class DistrhoUINotes : public QtUI
 {
     Q_OBJECT
 
diff --git a/source/libs/distrho/DistrhoUIMain.cpp b/source/libs/distrho/DistrhoUIMain.cpp
index 4d2d192ed..7193abbed 100644
--- a/source/libs/distrho/DistrhoUIMain.cpp
+++ b/source/libs/distrho/DistrhoUIMain.cpp
@@ -26,8 +26,8 @@
 // nothing
 #endif
 
-#ifdef DISTRHO_UI_QT4
-# include "src/DistrhoUIQt4.cpp"
+#ifdef DISTRHO_UI_QT
+# include "src/DistrhoUIQt.cpp"
 #else
 # include "src/DistrhoUIOpenGL.cpp"
 #endif
diff --git a/source/libs/distrho/DistrhoUIQt4.hpp b/source/libs/distrho/DistrhoUIQt4.hpp
deleted file mode 100644
index 029ec4120..000000000
--- a/source/libs/distrho/DistrhoUIQt4.hpp
+++ /dev/null
@@ -1,84 +0,0 @@
-/*
- * DISTRHO Plugin Toolkit (DPT)
- * Copyright (C) 2012-2013 Filipe Coelho <falktx@falktx.com>
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU Lesser General Public License for more details.
- *
- * For a full copy of the license see the LGPL.txt file
- */
-
-#ifndef __DISTRHO_UI_QT4_HPP__
-#define __DISTRHO_UI_QT4_HPP__
-
-#include "DistrhoUI.hpp"
-
-#include <QtCore/Qt>
-
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 0, 0))
-# include <QtWidgets/QWidget>
-#else
-# include <QtGui/QWidget>
-#endif
-
-START_NAMESPACE_DISTRHO
-
-// -------------------------------------------------
-// Qt4 UI
-
-class Qt4UI : public UI,
-              public QWidget
-{
-public:
-    Qt4UI();
-    virtual ~Qt4UI();
-
-protected:
-    // ---------------------------------------------
-    // Information
-
-    virtual bool d_resizable() { return false; }
-    virtual uint d_minimumWidth() { return 100; }
-    virtual uint d_minimumHeight() { return 100; }
-
-    // ---------------------------------------------
-    // DSP Callbacks
-
-    virtual void d_parameterChanged(uint32_t index, float value) = 0;
-#if DISTRHO_PLUGIN_WANT_PROGRAMS
-    virtual void d_programChanged(uint32_t index) = 0;
-#endif
-#if DISTRHO_PLUGIN_WANT_STATE
-    virtual void d_stateChanged(const char* key, const char* value) = 0;
-#endif
-#if DISTRHO_PLUGIN_IS_SYNTH
-    virtual void d_noteReceived(bool onOff, uint8_t channel, uint8_t note, uint8_t velocity) = 0;
-#endif
-
-    // ---------------------------------------------
-    // UI Callbacks
-
-    virtual void d_uiIdle() {}
-
-private:
-    friend class UIInternal;
-
-    // ---------------------------------------------
-    // Implement resize internally
-
-    void         d_uiResize(unsigned int width, unsigned int height);
-    unsigned int d_width() const { return width(); }
-    unsigned int d_height() const { return height(); }
-};
-
-// -------------------------------------------------
-
-END_NAMESPACE_DISTRHO
-
-#endif // __DISTRHO_UI_QT4_HPP__
diff --git a/source/libs/distrho/dgl/Window.hpp b/source/libs/distrho/dgl/Window.hpp
index 5c0891edd..9ee6b82f3 100644
--- a/source/libs/distrho/dgl/Window.hpp
+++ b/source/libs/distrho/dgl/Window.hpp
@@ -45,8 +45,8 @@ public:
     void setWindowTitle(const char* title);
 
     App* getApp() const;
-    int getModifiers();
-    intptr_t getWindowId();
+    int getModifiers() const;
+    intptr_t getWindowId() const;
 
     void addWidget(Widget* widget);
     void removeWidget(Widget* widget);
diff --git a/source/libs/distrho/dgl/src/Window.cpp b/source/libs/distrho/dgl/src/Window.cpp
index 350a65e51..5327d97fe 100644
--- a/source/libs/distrho/dgl/src/Window.cpp
+++ b/source/libs/distrho/dgl/src/Window.cpp
@@ -284,12 +284,12 @@ public:
         return kApp;
     }
 
-    int getModifiers()
+    int getModifiers() const
     {
         return puglGetModifiers(kView);
     }
 
-    intptr_t getWindowId()
+    intptr_t getWindowId() const
     {
         return puglGetNativeWindow(kView);
     }
@@ -556,12 +556,12 @@ App* Window::getApp() const
     return kPrivate->getApp();
 }
 
-int Window::getModifiers()
+int Window::getModifiers() const
 {
     return kPrivate->getModifiers();
 }
 
-intptr_t Window::getWindowId()
+intptr_t Window::getWindowId() const
 {
     return kPrivate->getWindowId();
 }
diff --git a/source/libs/distrho/src/DistrhoDefines.h b/source/libs/distrho/src/DistrhoDefines.h
index 982f64abe..f82f15452 100644
--- a/source/libs/distrho/src/DistrhoDefines.h
+++ b/source/libs/distrho/src/DistrhoDefines.h
@@ -86,7 +86,7 @@
 # define USE_NAMESPACE_DISTRHO
 #endif
 
-#ifndef DISTRHO_UI_QT4
+#ifndef DISTRHO_UI_QT
 # define DISTRHO_UI_OPENGL
 #endif
 
diff --git a/source/libs/distrho/src/DistrhoPluginInternal.hpp b/source/libs/distrho/src/DistrhoPluginInternal.hpp
index c32e8f48d..53ce9025f 100644
--- a/source/libs/distrho/src/DistrhoPluginInternal.hpp
+++ b/source/libs/distrho/src/DistrhoPluginInternal.hpp
@@ -69,8 +69,8 @@ struct PluginPrivateData {
 #endif
           timePos()
     {
-        assert(d_lastBufferSize != 0);
-        assert(d_lastSampleRate != 0.0);
+        assert(bufferSize != 0);
+        assert(sampleRate != 0.0);
     }
 
     ~PluginPrivateData()
@@ -300,19 +300,19 @@ public:
 
     // ---------------------------------------------
 
-    void setBufferSize(uint32_t bufferSize, bool callback = false)
+    void setBufferSize(uint32_t bufferSize, bool doCallback = false)
     {
         assert(kData != nullptr && kPlugin && bufferSize >= 2);
 
         if (kData != nullptr)
         {
-            if (callback && kData->bufferSize == bufferSize)
-                callback = false;
+            if (doCallback && kData->bufferSize == bufferSize)
+                doCallback = false;
 
             kData->bufferSize = bufferSize;
         }
 
-        if (kPlugin != nullptr && callback)
+        if (kPlugin != nullptr && doCallback)
         {
             kPlugin->d_deactivate();
             kPlugin->d_bufferSizeChanged(bufferSize);
@@ -320,19 +320,19 @@ public:
         }
     }
 
-    void setSampleRate(double sampleRate, bool callback = false)
+    void setSampleRate(double sampleRate, bool doCallback = false)
     {
         assert(kData != nullptr && kPlugin != nullptr && sampleRate > 0.0);
 
         if (kData != nullptr)
         {
-            if (callback && kData->sampleRate == sampleRate)
-                callback = false;
+            if (doCallback && kData->sampleRate == sampleRate)
+                doCallback = false;
 
             kData->sampleRate = sampleRate;
         }
 
-        if (kPlugin != nullptr && callback)
+        if (kPlugin != nullptr && doCallback)
         {
             kPlugin->d_deactivate();
             kPlugin->d_sampleRateChanged(sampleRate);
diff --git a/source/libs/distrho/src/DistrhoUIInternal.hpp b/source/libs/distrho/src/DistrhoUIInternal.hpp
index f28e2b5ac..aa176ba71 100644
--- a/source/libs/distrho/src/DistrhoUIInternal.hpp
+++ b/source/libs/distrho/src/DistrhoUIInternal.hpp
@@ -24,19 +24,7 @@
 # include "../dgl/App.hpp"
 # include "../dgl/Window.hpp"
 #else
-# include "../DistrhoUIQt4.hpp"
-# include <QtGui/QMouseEvent>
-# include <QtGui/QResizeEvent>
-# if (QT_VERSION >= QT_VERSION_CHECK(5, 0, 0))
-#  include <QtWidgets/QSizeGrip>
-#  include <QtWidgets/QVBoxLayout>
-# else
-#  include <QtGui/QSizeGrip>
-#  include <QtGui/QVBoxLayout>
-#  ifdef Q_WS_X11
-#   include <QtGui/QX11EmbedWidget>
-#  endif
-# endif
+# include "../DistrhoUIQt.hpp"
 #endif
 
 #include <cassert>
@@ -55,23 +43,6 @@ extern double d_lastUiSampleRate;
 
 // -------------------------------------------------
 
-#ifdef DISTRHO_UI_QT4
-# ifdef Q_WS_X11
-class QEmbedWidget : public QX11EmbedWidget
-# else
-class QEmbedWidget : public QWidget
-# endif
-{
-public:
-    QEmbedWidget(WId parent);
-    ~QEmbedWidget();
-
-    WId containerWinId() const;
-};
-#endif
-
-// -------------------------------------------------
-
 struct UIPrivateData {
     // DSP
     double   sampleRate;
@@ -95,7 +66,7 @@ struct UIPrivateData {
           uiResizeCallbackFunc(nullptr),
           ptr(nullptr)
     {
-        assert(d_lastUiSampleRate != 0.0);
+        assert(sampleRate != 0.0);
     }
 
     ~UIPrivateData()
@@ -135,29 +106,35 @@ struct UIPrivateData {
 
 // -------------------------------------------------
 
-#ifdef DISTRHO_UI_QT4
-class UIInternal : public QObject // needed for eventFilter()
-#else
 class UIInternal
-#endif
 {
 public:
     UIInternal(void* ptr, intptr_t winId, editParamFunc editParamCall, setParamFunc setParamCall, setStateFunc setStateCall, sendNoteFunc sendNoteCall, uiResizeFunc uiResizeCall)
-#ifdef DISTRHO_UI_QT4
-        : qtGrip(nullptr),
-          qtWidget(nullptr),
-#else
+#ifdef DISTRHO_UI_OPENGL
         : glApp(),
           glWindow(&glApp, winId),
+#else
+        :
 #endif
           kUi(createUI()),
           kData((kUi != nullptr) ? kUi->pData : nullptr)
     {
         assert(kUi != nullptr);
+
+        if (kUi == nullptr)
+            return;
+
+#ifdef DISTRHO_UI_OPENGL
         assert(winId != 0);
 
-        if (kUi == nullptr || winId == 0)
+        if (winId == 0)
+            return;
+#else
+        assert(winId == 0);
+
+        if (winId != 0)
             return;
+#endif
 
         kData->ptr = ptr;
         kData->editParamCallbackFunc = editParamCall;
@@ -165,21 +142,12 @@ public:
         kData->setStateCallbackFunc  = setStateCall;
         kData->sendNoteCallbackFunc  = sendNoteCall;
         kData->uiResizeCallbackFunc  = uiResizeCall;
-
-#ifdef DISTRHO_UI_QT4
-        createWindow(winId);
-#endif
     }
 
     ~UIInternal()
     {
         if (kUi != nullptr)
-        {
-#ifdef DISTRHO_UI_QT4
-            destroyWindow();
-#endif
             delete kUi;
-        }
     }
 
     // ---------------------------------------------
@@ -246,7 +214,7 @@ public:
 
     void idle()
     {
-#ifdef DISTRHO_UI_QT4
+#ifdef DISTRHO_UI_QT
         assert(kUi != nullptr);
 
         if (kUi != nullptr)
@@ -256,106 +224,27 @@ public:
 #endif
     }
 
-    intptr_t getWinId()
+#ifdef DISTRHO_UI_QT
+    QtUI* getQtUI() const
     {
-#ifdef DISTRHO_UI_QT4
-        assert(qtWidget != nullptr);
-        return (qtWidget != nullptr) ? (intptr_t)qtWidget->winId() : 0;
-#else
-        return glWindow.getWindowId();
-#endif
+        return (QtUI*)kUi;
     }
 
-    // ---------------------------------------------
-
-#ifdef DISTRHO_UI_QT4
-    void createWindow(intptr_t parent)
+    bool resizable() const
     {
-        assert(kUi != nullptr);
-        assert(kData != nullptr);
-        assert(qtGrip == nullptr);
-        assert(qtWidget == nullptr);
-
-        if (kUi == nullptr)
-            return;
-        if (kData == nullptr)
-            return;
-        if (qtGrip != nullptr)
-            return;
-        if (qtWidget != nullptr)
-            return;
-
-        Qt4UI* qt4Ui = (Qt4UI*)kUi;
-
-        // create embedable widget
-        qtWidget = new QEmbedWidget((WId)parent);
-
-        // set layout
-        qtWidget->setLayout(new QVBoxLayout(qtWidget));
-        qtWidget->layout()->addWidget(qt4Ui);
-        qtWidget->layout()->setContentsMargins(0, 0, 0, 0);
-        qtWidget->setFixedSize(kUi->d_width(), kUi->d_height());
-
-        // set resize grip
-        if (qt4Ui->d_resizable())
-        {
-            // listen for resize on the plugin widget
-            qt4Ui->installEventFilter(this);
-
-            // create resize grip on bottom-right
-            qtGrip = new QSizeGrip(qtWidget);
-            qtGrip->resize(qtGrip->sizeHint());
-            qtGrip->setCursor(Qt::SizeFDiagCursor);
-            qtGrip->move(kUi->d_width() - qtGrip->width(), kUi->d_height() - qtGrip->height());
-            qtGrip->show();
-            qtGrip->raise();
-            qtGrip->installEventFilter(this);
-        }
-
-        // show it
-        qtWidget->show();
+        return ((QtUI*)kUi)->d_resizable();
     }
-
-    void destroyWindow()
+#else
+    intptr_t getWinId()
     {
-        assert(kData != nullptr);
-        assert(qtWidget != nullptr);
-
-        if (kData == nullptr)
-            return;
-        if (qtWidget == nullptr)
-            return;
-
-        Qt4UI* qt4Ui = (Qt4UI*)kUi;
-
-        // remove main widget, to prevent it from being auto-deleted
-        qt4Ui->hide();
-        qtWidget->layout()->removeWidget(qt4Ui);
-        qt4Ui->setParent(nullptr);
-        qt4Ui->close();
-
-        qtWidget->close();
-        qtWidget->removeEventFilter(this);
-
-        if (qtGrip != nullptr)
-        {
-            qtGrip->removeEventFilter(this);
-            delete qtGrip;
-            qtGrip = nullptr;
-        }
-
-        delete qtWidget;
-        qtWidget = nullptr;
+        return glWindow.getWindowId();
     }
 #endif
 
     // ---------------------------------------------
 
 private:
-#ifdef DISTRHO_UI_QT4
-    QSizeGrip*    qtGrip;
-    QEmbedWidget* qtWidget;
-#else
+#ifdef DISTRHO_UI_OPENGL
     App    glApp;
     Window glWindow;
 #endif
@@ -363,66 +252,6 @@ private:
 protected:
     UI* const kUi;
     UIPrivateData* const kData;
-
-#ifdef DISTRHO_UI_QT4
-    bool eventFilter(QObject* obj, QEvent* event)
-    {
-        assert(kUi != nullptr);
-        assert(kData != nullptr);
-        //assert(qtGrip != nullptr);
-        assert(qtWidget != nullptr);
-
-        if (kUi == nullptr)
-            return false;
-        if (kData == nullptr)
-            return false;
-        if (qtGrip == nullptr)
-            return false;
-        if (qtWidget == nullptr)
-            return false;
-
-        Qt4UI* qt4Ui = (Qt4UI*)kUi;
-
-        if (obj == nullptr)
-        {
-            // nothing
-        }
-        else if (obj == qtGrip)
-        {
-            if (event->type() == QEvent::MouseMove)
-            {
-                QMouseEvent* mEvent = (QMouseEvent*)event;
-
-                if (mEvent->button() == Qt::LeftButton)
-                {
-                    unsigned int width  = qt4Ui->d_width()  + mEvent->x() - qtGrip->width();
-                    unsigned int height = qt4Ui->d_height() + mEvent->y() - qtGrip->height();
-
-                    if (width < qt4Ui->d_minimumWidth())
-                        width = qt4Ui->d_minimumWidth();
-                    if (height < qt4Ui->d_minimumHeight())
-                        height = qt4Ui->d_minimumHeight();
-
-                    qt4Ui->setFixedSize(width, height);
-
-                    return true;
-                }
-            }
-        }
-        else if (obj == qt4Ui && event->type() == QEvent::Resize)
-        {
-            QResizeEvent* rEvent = (QResizeEvent*)event;
-            const QSize&  size   = rEvent->size();
-
-            qtWidget->setFixedSize(size.width(), size.height());
-            qtGrip->move(size.width() - qtGrip->width(), size.height() - qtGrip->height());
-
-            kUi->d_uiResize(size.width(), size.height());
-        }
-
-        return QObject::eventFilter(obj, event);
-    }
-#endif
 };
 
 // -------------------------------------------------
diff --git a/source/libs/distrho/src/DistrhoUIQt4.cpp b/source/libs/distrho/src/DistrhoUIQt.cpp
similarity index 56%
rename from source/libs/distrho/src/DistrhoUIQt4.cpp
rename to source/libs/distrho/src/DistrhoUIQt.cpp
index 29b8a4c90..1402ec469 100644
--- a/source/libs/distrho/src/DistrhoUIQt4.cpp
+++ b/source/libs/distrho/src/DistrhoUIQt.cpp
@@ -16,57 +16,31 @@
 
 #include "DistrhoUIInternal.hpp"
 
-START_NAMESPACE_DISTRHO
-
-// -------------------------------------------------
-// QEmbedWidget
-
-QEmbedWidget::QEmbedWidget(WId id)
-#ifdef Q_WS_X11
-    : QX11EmbedWidget()
-#else
-    : QWidget()
-#endif
-{
-#ifdef Q_WS_X11
-    embedInto(id);
-#else
-    create(id, false, false);
-#endif
-}
+#include <QtGui/QResizeEvent>
 
-QEmbedWidget::~QEmbedWidget()
-{
-}
-
-WId QEmbedWidget::containerWinId() const
-{
-#ifdef Q_WS_X11
-    return QX11EmbedWidget::containerWinId();
-#else
-    return winId();
-#endif
-}
+START_NAMESPACE_DISTRHO
 
 // -------------------------------------------------
 // Qt4UI
 
-Qt4UI::Qt4UI()
+QtUI::QtUI()
     : UI(),
       QWidget(nullptr)
 {
 }
 
-Qt4UI::~Qt4UI()
+QtUI::~QtUI()
 {
 }
 
-// -------------------------------------------------
-// Implement resize internally
-
-void Qt4UI::d_uiResize(unsigned int width, unsigned int height)
+void QtUI::setSize(unsigned int width, unsigned int height)
 {
-    UI::d_uiResize(width, height);
+    if (d_resizable())
+        resize(width, height);
+    else
+        setFixedSize(width, height);
+
+    d_uiResize(width, height);
 }
 
 // -------------------------------------------------