Merge branch '4.7' of scm.dev.nokia.troll.no:qt/oslo-staging-2 into 4.7

13 files changed, 162 insertions, 72 deletions

diff --git a/src/opengl/gl2paintengineex/qgl2pexvertexarray_p.h b/src/opengl/gl2paintengineex/qgl2pexvertexarray_p.h
index adc69ee..46029b9 100644
--- a/src/opengl/gl2paintengineex/qgl2pexvertexarray_p.h
+++ b/src/opengl/gl2paintengineex/qgl2pexvertexarray_p.h
@@ -100,8 +100,10 @@ class QGL2PEXVertexArray
 {
 public:
     QGL2PEXVertexArray() :
+        vertexArray(0), vertexArrayStops(0),
         maxX(-2e10), maxY(-2e10), minX(2e10), minY(2e10),
-        boundingRectDirty(true) {}
+        boundingRectDirty(true)
+    { }
     
     inline void addRect(const QRectF &rect)
     {
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h b/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
index 6ba0c42..0a046dc 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
@@ -177,6 +177,7 @@ public:
             ctx(0),
             useSystemClip(true),
             elementIndicesVBOId(0),
+            opacityArray(0),
             snapToPixelGrid(false),
             addOffset(false),
             nativePaintingActive(false),
diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
index 994c1c9..410cf21 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
@@ -42,6 +42,10 @@
 #include "qtextureglyphcache_gl_p.h"
 #include "qpaintengineex_opengl2_p.h"
 
+#if defined QT_OPENGL_ES_2 && !defined(QT_NO_EGL)
+#include "private/qeglcontext_p.h"
+#endif
+
 QT_BEGIN_NAMESPACE
 
 #ifdef Q_WS_WIN
@@ -49,12 +53,19 @@ extern Q_GUI_EXPORT bool qt_cleartype_enabled;
 #endif
 
 QGLTextureGlyphCache::QGLTextureGlyphCache(QGLContext *context, QFontEngineGlyphCache::Type type, const QTransform &matrix)
-    : QTextureGlyphCache(type, matrix)
+    : QImageTextureGlyphCache(type, matrix)
     , ctx(context)
     , m_width(0)
     , m_height(0)
 {
-    glGenFramebuffers(1, &m_fbo);
+    // broken FBO readback is a bug in the SGX 1.3 and 1.4 drivers for the N900 where
+    // copying between FBO's is broken if the texture is either GL_ALPHA or POT. The
+    // workaround is to use a system-memory copy of the glyph cache for this device.
+    // Switching to NPOT and GL_RGBA would both cost a lot more graphics memory and
+    // be slower, so that is not desireable.
+    if (!ctx->d_ptr->workaround_brokenFBOReadBack)
+        glGenFramebuffers(1, &m_fbo);
+
     connect(QGLSignalProxy::instance(), SIGNAL(aboutToDestroyContext(const QGLContext*)),
             SLOT(contextDestroyed(const QGLContext*)));
 }
@@ -63,7 +74,9 @@ QGLTextureGlyphCache::~QGLTextureGlyphCache()
 {
     if (ctx) {
         QGLShareContextScope scope(ctx);
-        glDeleteFramebuffers(1, &m_fbo);
+
+        if (!ctx->d_ptr->workaround_brokenFBOReadBack)
+            glDeleteFramebuffers(1, &m_fbo);
 
         if (m_width || m_height)
             glDeleteTextures(1, &m_texture);
@@ -72,6 +85,18 @@ QGLTextureGlyphCache::~QGLTextureGlyphCache()
 
 void QGLTextureGlyphCache::createTextureData(int width, int height)
 {
+    // create in QImageTextureGlyphCache baseclass is meant to be called
+    // only to create the initial image and does not preserve the content,
+    // so we don't call when this function is called from resize.
+    if (ctx->d_ptr->workaround_brokenFBOReadBack && image().isNull())
+        QImageTextureGlyphCache::createTextureData(width, height);
+
+    // Make the lower glyph texture size 16 x 16.
+    if (width < 16)
+        width = 16;
+    if (height < 16)
+        height = 16;
+
     glGenTextures(1, &m_texture);
     glBindTexture(GL_TEXTURE_2D, m_texture);
 
@@ -93,14 +118,28 @@ void QGLTextureGlyphCache::createTextureData(int width, int height)
 
 void QGLTextureGlyphCache::resizeTextureData(int width, int height)
 {
-    // ### the QTextureGlyphCache API needs to be reworked to allow
-    // ### resizeTextureData to fail
-
     int oldWidth = m_width;
     int oldHeight = m_height;
 
+    // Make the lower glyph texture size 16 x 16.
+    if (width < 16)
+        width = 16;
+    if (height < 16)
+        height = 16;
+
     GLuint oldTexture = m_texture;
     createTextureData(width, height);
+    
+    if (ctx->d_ptr->workaround_brokenFBOReadBack) {
+        QImageTextureGlyphCache::resizeTextureData(width, height);
+        Q_ASSERT(image().depth() == 8);
+        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, oldWidth, oldHeight, GL_ALPHA, GL_UNSIGNED_BYTE, image().constBits());
+        glDeleteTextures(1, &oldTexture);
+        return;
+    }
+
+    // ### the QTextureGlyphCache API needs to be reworked to allow
+    // ### resizeTextureData to fail
 
     glBindFramebuffer(GL_FRAMEBUFFER_EXT, m_fbo);
 
@@ -159,20 +198,7 @@ void QGLTextureGlyphCache::resizeTextureData(int width, int height)
 
     glBindTexture(GL_TEXTURE_2D, m_texture);
 
-#ifdef QT_OPENGL_ES_2
-    QDataBuffer<uchar> buffer(4*oldWidth*oldHeight);
-    buffer.resize(4*oldWidth*oldHeight);
-    glReadPixels(0, 0, oldWidth, oldHeight, GL_RGBA, GL_UNSIGNED_BYTE, buffer.data());
-
-    // do an in-place conversion from GL_RGBA to GL_ALPHA
-    for (int i=0; i<oldWidth*oldHeight; ++i)
-        buffer.data()[i] = buffer.at(4*i + 3);
-
-    glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, oldWidth, oldHeight,
-                    GL_ALPHA, GL_UNSIGNED_BYTE, buffer.data());
-#else
     glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, oldWidth, oldHeight);
-#endif
 
     glFramebufferRenderbuffer(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
                               GL_RENDERBUFFER_EXT, 0);
@@ -187,6 +213,21 @@ void QGLTextureGlyphCache::resizeTextureData(int width, int height)
 
 void QGLTextureGlyphCache::fillTexture(const Coord &c, glyph_t glyph)
 {
+    if (ctx->d_ptr->workaround_brokenFBOReadBack) {
+        QImageTextureGlyphCache::fillTexture(c, glyph);
+
+        glBindTexture(GL_TEXTURE_2D, m_texture);
+        const QImage &texture = image();
+        const uchar *bits = texture.constBits();
+        bits += c.y * texture.bytesPerLine() + c.x;
+        for (int i=0; i<c.h; ++i) {
+            glTexSubImage2D(GL_TEXTURE_2D, 0, c.x, c.y + i, c.w, 1, GL_ALPHA, GL_UNSIGNED_BYTE, bits);
+            bits += texture.bytesPerLine();
+        }
+
+        return;
+    }
+
     QImage mask = textureMapForGlyph(glyph);
     const int maskWidth = mask.width();
     const int maskHeight = mask.height();
@@ -235,17 +276,6 @@ void QGLTextureGlyphCache::fillTexture(const Coord &c, glyph_t glyph)
     }
 }
 
-int QGLTextureGlyphCache::glyphMargin() const
-{
-#if defined(Q_WS_MAC)
-    return 2;
-#elif defined (Q_WS_X11)
-    return 0;
-#else
-    return m_type == QFontEngineGlyphCache::Raster_RGBMask ? 2 : 0;
-#endif
-}
-
 int QGLTextureGlyphCache::glyphPadding() const
 {
     return 1;
diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h b/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
index 75c2bb1..6bcd655 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
@@ -62,7 +62,7 @@ QT_BEGIN_NAMESPACE
 
 class QGL2PaintEngineExPrivate;
 
-class Q_OPENGL_EXPORT QGLTextureGlyphCache : public QObject, public QTextureGlyphCache
+class Q_OPENGL_EXPORT QGLTextureGlyphCache : public QObject, public QImageTextureGlyphCache
 {
     Q_OBJECT
 public:
@@ -72,7 +72,6 @@ public:
     virtual void createTextureData(int width, int height);
     virtual void resizeTextureData(int width, int height);
     virtual void fillTexture(const Coord &c, glyph_t glyph);
-    virtual int glyphMargin() const;
     virtual int glyphPadding() const;
 
     inline GLuint texture() const { return m_texture; }
diff --git a/src/opengl/gl2paintengineex/qtriangulatingstroker.cpp b/src/opengl/gl2paintengineex/qtriangulatingstroker.cpp
index f677ce1..9bc099d 100644
--- a/src/opengl/gl2paintengineex/qtriangulatingstroker.cpp
+++ b/src/opengl/gl2paintengineex/qtriangulatingstroker.cpp
@@ -481,7 +481,8 @@ static void qdashprocessor_cubicTo(qreal, qreal, qreal, qreal, qreal, qreal, voi
 }
 
 QDashedStrokeProcessor::QDashedStrokeProcessor()
-    : m_dash_stroker(0), m_inv_scale(1)
+    : m_points(0), m_types(0),
+      m_dash_stroker(0), m_inv_scale(1)
 {
     m_dash_stroker.setMoveToHook(qdashprocessor_moveTo);
     m_dash_stroker.setLineToHook(qdashprocessor_lineTo);
@@ -499,6 +500,8 @@ void QDashedStrokeProcessor::process(const QVectorPath &path, const QPen &pen, c
 
     m_points.reset();
     m_types.reset();
+    m_points.reserve(path.elementCount());
+    m_types.reserve(path.elementCount());
 
     qreal width = qpen_widthf(pen);
     if (width == 0)
diff --git a/src/opengl/gl2paintengineex/qtriangulatingstroker_p.h b/src/opengl/gl2paintengineex/qtriangulatingstroker_p.h
index 956d7cc..ab27ed6 100644
--- a/src/opengl/gl2paintengineex/qtriangulatingstroker_p.h
+++ b/src/opengl/gl2paintengineex/qtriangulatingstroker_p.h
@@ -54,6 +54,7 @@ QT_BEGIN_NAMESPACE
 class QTriangulatingStroker
 {
 public:
+    QTriangulatingStroker() : m_vertices(0) {}
     void process(const QVectorPath &path, const QPen &pen, const QRectF &clip);
 
     inline int vertexCount() const { return m_vertices.size(); }
diff --git a/src/opengl/gl2paintengineex/qtriangulator.cpp b/src/opengl/gl2paintengineex/qtriangulator.cpp
index ce917ff..df7cbc2 100644
--- a/src/opengl/gl2paintengineex/qtriangulator.cpp
+++ b/src/opengl/gl2paintengineex/qtriangulator.cpp
@@ -510,6 +510,7 @@ template <class T>
 class QMaxHeap
 {
 public:
+    QMaxHeap() : m_data(0) {}
     inline int size() const {return m_data.size();}
     inline bool empty() const {return m_data.isEmpty();}
     inline bool isEmpty() const {return m_data.isEmpty();}
@@ -1299,7 +1300,8 @@ public:
     class ComplexToSimple
     {
     public:
-        inline ComplexToSimple(QTriangulator *parent) : m_parent(parent) { }
+        inline ComplexToSimple(QTriangulator *parent) : m_parent(parent),
+            m_edges(0), m_events(0), m_splits(0) { }
         void decompose();
     private:
         struct Edge
@@ -1412,7 +1414,7 @@ public:
     class SimpleToMonotone
     {
     public:
-        inline SimpleToMonotone(QTriangulator *parent) : m_parent(parent) { }
+        inline SimpleToMonotone(QTriangulator *parent) : m_parent(parent), m_edges(0), m_upperVertex(0) { }
         void decompose();
     private:
         enum VertexType {MergeVertex, EndVertex, RegularVertex, StartVertex, SplitVertex};
@@ -1486,7 +1488,7 @@ public:
         int m_length;
     };
 
-    inline QTriangulator() { }
+    inline QTriangulator() : m_vertices(0) { }
 
     // Call this only once.
     void initialize(const qreal *polygon, int count, uint hint, const QTransform &matrix);
@@ -2709,7 +2711,7 @@ void QTriangulator::SimpleToMonotone::monotoneDecomposition()
         return;
 
     Q_ASSERT(!m_edgeList.root);
-    QDataBuffer<QPair<int, int> > diagonals;
+    QDataBuffer<QPair<int, int> > diagonals(m_upperVertex.size());
 
     int i = 0;
     for (int index = 1; index < m_edges.size(); ++index) {
@@ -2853,7 +2855,7 @@ bool QTriangulator::SimpleToMonotone::CompareVertices::operator () (int i, int j
 void QTriangulator::MonotoneToTriangles::decompose()
 {
     QVector<quint32> result;
-    QDataBuffer<int> stack;
+    QDataBuffer<int> stack(m_parent->m_indices.size());
     m_first = 0;
     // Require at least three more indices.
     while (m_first + 3 <= m_parent->m_indices.size()) {
diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index cfacf26..922a96c 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -1612,6 +1612,9 @@ void QGLContextPrivate::init(QPaintDevice *dev, const QGLFormat &format)
     current_fbo = 0;
     default_fbo = 0;
     active_engine = 0;
+    workaround_needsFullClearOnEveryFrame = false;
+    workaround_brokenFBOReadBack = false;
+    workaroundsCached = false;
     for (int i = 0; i < QT_GL_VERTEX_ARRAY_TRACKED_COUNT; ++i)
         vertexAttributeArraysEnabledState[i] = false;
 }
@@ -1723,7 +1726,6 @@ QGLTextureCache::QGLTextureCache()
 
 QGLTextureCache::~QGLTextureCache()
 {
-    Q_ASSERT(size() == 0);
     QImagePixmapCleanupHooks::instance()->removePixmapDataModificationHook(cleanupTexturesForPixampData);
     QImagePixmapCleanupHooks::instance()->removePixmapDataDestructionHook(cleanupBeforePixmapDestruction);
     QImagePixmapCleanupHooks::instance()->removeImageHook(cleanupTexturesForCacheKey);
@@ -2773,23 +2775,27 @@ static void qDrawTextureRect(const QRectF &target, GLint textureWidth, GLint tex
 /*!
     \since 4.4
 
-    Draws the given texture, \a textureId, to the given target rectangle,
-    \a target, in OpenGL model space. The \a textureTarget should be a 2D
-    texture target.
+    This function supports the following use cases:
+
+    \list
+    \i On OpenGL and OpenGL ES 1.x it draws the given texture, \a textureId,
+    to the given target rectangle, \a target, in OpenGL model space. The
+    \a textureTarget should be a 2D texture target.
+    \i On OpenGL and OpenGL ES 2.x, if a painter is active, not inside a
+    beginNativePainting / endNativePainting block, and uses the
+    engine with type QPaintEngine::OpenGL2, the function will draw the given
+    texture, \a textureId, to the given target rectangle, \a target,
+    respecting the current painter state. This will let you draw a texture
+    with the clip, transform, render hints, and composition mode set by the
+    painter. Note that the texture target needs to be GL_TEXTURE_2D for this
+    use case, and that this is the only supported use case under OpenGL ES 2.x.
+    \endlist
 
-    \note This function is not supported under OpenGL/ES 2.0.
 */
 void QGLContext::drawTexture(const QRectF &target, GLuint textureId, GLenum textureTarget)
 {
-#ifndef QT_OPENGL_ES_2
-#ifdef QT_OPENGL_ES
-    if (textureTarget != GL_TEXTURE_2D) {
-        qWarning("QGLContext::drawTexture(): texture target must be GL_TEXTURE_2D on OpenGL ES");
-        return;
-    }
-#else
-
-     if (d_ptr->active_engine && 
+#if !defined(QT_OPENGL_ES) || defined(QT_OPENGL_ES_2)
+     if (d_ptr->active_engine &&
          d_ptr->active_engine->type() == QPaintEngine::OpenGL2) {
          QGL2PaintEngineEx *eng = static_cast<QGL2PaintEngineEx*>(d_ptr->active_engine);
          if (!eng->isNativePaintingActive()) {
@@ -2799,7 +2805,15 @@ void QGLContext::drawTexture(const QRectF &target, GLuint textureId, GLenum text
                 return;
         }
      }
+#endif
 
+#ifndef QT_OPENGL_ES_2
+#ifdef QT_OPENGL_ES
+    if (textureTarget != GL_TEXTURE_2D) {
+        qWarning("QGLContext::drawTexture(): texture target must be GL_TEXTURE_2D on OpenGL ES");
+        return;
+    }
+#else
     const bool wasEnabled = glIsEnabled(GL_TEXTURE_2D);
     GLint oldTexture;
     glGetIntegerv(GL_TEXTURE_BINDING_2D, &oldTexture);
@@ -2821,7 +2835,7 @@ void QGLContext::drawTexture(const QRectF &target, GLuint textureId, GLenum text
     Q_UNUSED(target);
     Q_UNUSED(textureId);
     Q_UNUSED(textureTarget);
-    qWarning("drawTexture(const QRectF &target, GLuint textureId, GLenum textureTarget) not supported with OpenGL ES/2.0");
+    qWarning("drawTexture() with OpenGL ES 2.0 requires an active OpenGL2 paint engine");
 #endif
 }
 
@@ -2836,14 +2850,26 @@ void QGLContext::drawTexture(const QRectF &target, QMacCompatGLuint textureId, Q
 /*!
     \since 4.4
 
-    Draws the given texture at the given \a point in OpenGL model
-    space. The \a textureTarget should be a 2D texture target.
+    This function supports the following use cases:
+
+    \list
+    \i By default it draws the given texture, \a textureId,
+    at the given \a point in OpenGL model space. The
+    \a textureTarget should be a 2D texture target.
+    \i If a painter is active, not inside a
+    beginNativePainting / endNativePainting block, and uses the
+    engine with type QPaintEngine::OpenGL2, the function will draw the given
+    texture, \a textureId, at the given \a point,
+    respecting the current painter state. This will let you draw a texture
+    with the clip, transform, render hints, and composition mode set by the
+    painter. Note that the texture target needs to be GL_TEXTURE_2D for this
+    use case.
+    \endlist
 
-    \note This function is not supported under OpenGL/ES.
+    \note This function is not supported under any version of OpenGL ES.
 */
 void QGLContext::drawTexture(const QPointF &point, GLuint textureId, GLenum textureTarget)
 {
-    // this would be ok on OpenGL ES 2.0, but currently we don't have a define for that
 #ifdef QT_OPENGL_ES
     Q_UNUSED(point);
     Q_UNUSED(textureId);
@@ -2864,7 +2890,7 @@ void QGLContext::drawTexture(const QPointF &point, GLuint textureId, GLenum text
     glGetTexLevelParameteriv(textureTarget, 0, GL_TEXTURE_WIDTH, &textureWidth);
     glGetTexLevelParameteriv(textureTarget, 0, GL_TEXTURE_HEIGHT, &textureHeight);
 
-    if (d_ptr->active_engine && 
+    if (d_ptr->active_engine &&
         d_ptr->active_engine->type() == QPaintEngine::OpenGL2) {
         QGL2PaintEngineEx *eng = static_cast<QGL2PaintEngineEx*>(d_ptr->active_engine);
         if (!eng->isNativePaintingActive()) {
@@ -4911,11 +4937,8 @@ void QGLWidget::deleteTexture(QMacCompatGLuint id)
 /*!
     \since 4.4
 
-    Draws the given texture, \a textureId to the given target rectangle,
-    \a target, in OpenGL model space. The \a textureTarget should be a 2D
-    texture target.
-
-    Equivalent to the corresponding QGLContext::drawTexture().
+    Calls the corresponding QGLContext::drawTexture() on
+    this widget's context.
 */
 void QGLWidget::drawTexture(const QRectF &target, GLuint textureId, GLenum textureTarget)
 {
@@ -4935,10 +4958,8 @@ void QGLWidget::drawTexture(const QRectF &target, QMacCompatGLuint textureId, QM
 /*!
     \since 4.4
 
-    Draws the given texture, \a textureId, at the given \a point in OpenGL
-    model space. The \a textureTarget should be a 2D texture target.
-
-    Equivalent to the corresponding QGLContext::drawTexture().
+    Calls the corresponding QGLContext::drawTexture() on
+    this widget's context.
 */
 void QGLWidget::drawTexture(const QPointF &point, GLuint textureId, GLenum textureTarget)
 {
diff --git a/src/opengl/qgl.h b/src/opengl/qgl.h
index 92a064f..f297009 100644
--- a/src/opengl/qgl.h
+++ b/src/opengl/qgl.h
@@ -431,6 +431,7 @@ private:
     friend class QGLFramebufferObjectPrivate;
     friend class QGLFBOGLPaintDevice;
     friend class QGLPaintDevice;
+    friend class QGLWidgetGLPaintDevice;
     friend class QX11GLPixmapData;
     friend class QX11GLSharedContexts;
 private:
diff --git a/src/opengl/qgl_egl.cpp b/src/opengl/qgl_egl.cpp
index 0fbbbf9..44e8ae9 100644
--- a/src/opengl/qgl_egl.cpp
+++ b/src/opengl/qgl_egl.cpp
@@ -185,8 +185,26 @@ void QGLContext::makeCurrent()
         return;
     }
 
-    if (d->eglContext->makeCurrent(d->eglSurfaceForDevice()))
+    if (d->eglContext->makeCurrent(d->eglSurfaceForDevice())) {
         QGLContextPrivate::setCurrentContext(this);
+        if (!d->workaroundsCached) {
+            d->workaroundsCached = true;
+            const char *renderer = reinterpret_cast<const char *>(glGetString(GL_RENDERER));
+            if (strstr(renderer, "SGX") || strstr(renderer, "MBX")) {
+                // PowerVR MBX/SGX chips needs to clear all buffers when starting to render
+                // a new frame, otherwise there will be a performance penalty to pay for
+                // each frame.
+                d->workaround_needsFullClearOnEveryFrame = true;
+
+                // Older PowerVR SGX drivers (like the one in the N900) have a
+                // bug which prevents glCopyTexSubImage2D() to work with a POT
+                // or GL_ALPHA texture bound to an FBO. The only way to
+                // identify that driver is to check the EGL version number for it.
+                if (strstr(eglQueryString(d->eglContext->display(), EGL_VERSION), "1.3"))
+                    d->workaround_brokenFBOReadBack = true;
+            }
+        }
+    }
 }
 
 void QGLContext::doneCurrent()
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index f19e394..d92f963 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -345,7 +345,7 @@ public:
     HDC hbitmap_hdc;
 #endif
 #ifndef QT_NO_EGL
-    bool ownsEglContext;
+    uint ownsEglContext : 1;
     QEglContext *eglContext;
     EGLSurface eglSurface;
     void destroyEglSurfaceForDevice();
@@ -382,6 +382,12 @@ public:
     uint internal_context : 1;
     uint version_flags_cached : 1;
     uint extension_flags_cached : 1;
+
+    // workarounds for driver/hw bugs on different platforms
+    uint workaround_needsFullClearOnEveryFrame : 1;
+    uint workaround_brokenFBOReadBack : 1;
+    uint workaroundsCached : 1;
+
     QPaintDevice *paintDevice;
     QColor transpColor;
     QGLContext *q_ptr;
diff --git a/src/opengl/qglpaintdevice.cpp b/src/opengl/qglpaintdevice.cpp
index e874e85..e1dcbfd 100644
--- a/src/opengl/qglpaintdevice.cpp
+++ b/src/opengl/qglpaintdevice.cpp
@@ -175,7 +175,10 @@ void QGLWidgetGLPaintDevice::beginPaint()
             float alpha = c.alphaF();
             glClearColor(c.redF() * alpha, c.greenF() * alpha, c.blueF() * alpha, alpha);
         }
-        glClear(GL_COLOR_BUFFER_BIT);
+        if (context()->d_func()->workaround_needsFullClearOnEveryFrame)
+            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+        else
+            glClear(GL_COLOR_BUFFER_BIT);
     }
 }
 
diff --git a/src/opengl/qpaintengine_opengl.cpp b/src/opengl/qpaintengine_opengl.cpp
index 306fd8b..08a50cb 100644
--- a/src/opengl/qpaintengine_opengl.cpp
+++ b/src/opengl/qpaintengine_opengl.cpp
@@ -668,6 +668,7 @@ public:
         , last_created_state(0)
         , shader_ctx(0)
         , grad_palette(0)
+        , tess_points(0)
         , drawable_texture(0)
         , ref_cleaner(this)
         {}
@@ -1950,6 +1951,8 @@ void QOpenGLPaintEnginePrivate::pathToVertexArrays(const QPainterPath &path)
 
 void QOpenGLPaintEnginePrivate::drawVertexArrays()
 {
+    if (tess_points_stops.count() == 0)
+        return;
     glEnableClientState(GL_VERTEX_ARRAY);
     glVertexPointer(2, GL_DOUBLE, 0, tess_points.data());
     int previous_stop = 0;
@@ -3947,7 +3950,7 @@ void QOpenGLPaintEnginePrivate::strokeLines(const QPainterPath &path)
     enableClipping();
 }
 
-extern bool qt_scaleForTransform(const QTransform &transform, qreal *scale); // qtransform.cpp
+Q_GUI_EXPORT bool qt_scaleForTransform(const QTransform &transform, qreal *scale); // qtransform.cpp
 
 void QOpenGLPaintEnginePrivate::strokePath(const QPainterPath &path, bool use_cache)
 {