Performance: Convert QGLFormat to use implicit sharing

QGLFormat was being deep-copied many times per frame because of
code like this:

    if (context()->format().doubleBuffer()) { ...

This change modifies QGLFormat to use implicit sharing to reduce
the overhead of the above type of checks.

Reviewed-by: Sarah Smith

3 files changed, 56 insertions, 7 deletions

diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index ef07447..aa67677 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -349,13 +349,26 @@ QGLFormat::QGLFormat(QGL::FormatOptions options, int plane)
 }
 
 /*!
+    \internal
+*/
+void QGLFormat::detach()
+{
+    if (d->ref != 1) {
+        QGLFormatPrivate *newd = new QGLFormatPrivate(d);
+        if (!d->ref.deref())
+            delete d;
+        d = newd;
+    }
+}
+
+/*!
     Constructs a copy of \a other.
 */
 
 QGLFormat::QGLFormat(const QGLFormat &other)
 {
-    d = new QGLFormatPrivate;
-    *d = *other.d;
+    d = other.d;
+    d->ref.ref();
 }
 
 /*!
@@ -364,7 +377,12 @@ QGLFormat::QGLFormat(const QGLFormat &other)
 
 QGLFormat &QGLFormat::operator=(const QGLFormat &other)
 {
-    *d = *other.d;
+    if (d != other.d) {
+        other.d->ref.ref();
+        if (!d->ref.deref())
+            delete d;
+        d = other.d;
+    }
     return *this;
 }
 
@@ -373,7 +391,8 @@ QGLFormat &QGLFormat::operator=(const QGLFormat &other)
 */
 QGLFormat::~QGLFormat()
 {
-    delete d;
+    if (!d->ref.deref())
+        delete d;
 }
 
 /*!
@@ -649,6 +668,7 @@ int QGLFormat::samples() const
 */
 void QGLFormat::setSamples(int numSamples)
 {
+    detach();
     if (numSamples < 0) {
         qWarning("QGLFormat::setSamples: Cannot have negative number of samples per pixel %d", numSamples);
         return;
@@ -676,6 +696,7 @@ void QGLFormat::setSamples(int numSamples)
 */
 void QGLFormat::setSwapInterval(int interval)
 {
+    detach();
     d->swapInterval = interval;
 }
 
@@ -743,6 +764,7 @@ int QGLFormat::plane() const
 */
 void QGLFormat::setPlane(int plane)
 {
+    detach();
     d->pln = plane;
 }
 
@@ -754,6 +776,7 @@ void QGLFormat::setPlane(int plane)
 
 void QGLFormat::setOption(QGL::FormatOptions opt)
 {
+    detach();
     if (opt & 0xffff)
         d->opts |= opt;
     else
@@ -783,6 +806,7 @@ bool QGLFormat::testOption(QGL::FormatOptions opt) const
 */
 void QGLFormat::setDepthBufferSize(int size)
 {
+    detach();
     if (size < 0) {
         qWarning("QGLFormat::setDepthBufferSize: Cannot set negative depth buffer size %d", size);
         return;
@@ -809,6 +833,7 @@ int QGLFormat::depthBufferSize() const
 */
 void QGLFormat::setRedBufferSize(int size)
 {
+    detach();
     if (size < 0) {
         qWarning("QGLFormat::setRedBufferSize: Cannot set negative red buffer size %d", size);
         return;
@@ -837,6 +862,7 @@ int QGLFormat::redBufferSize() const
 */
 void QGLFormat::setGreenBufferSize(int size)
 {
+    detach();
     if (size < 0) {
         qWarning("QGLFormat::setGreenBufferSize: Cannot set negative green buffer size %d", size);
         return;
@@ -865,6 +891,7 @@ int QGLFormat::greenBufferSize() const
 */
 void QGLFormat::setBlueBufferSize(int size)
 {
+    detach();
     if (size < 0) {
         qWarning("QGLFormat::setBlueBufferSize: Cannot set negative blue buffer size %d", size);
         return;
@@ -892,6 +919,7 @@ int QGLFormat::blueBufferSize() const
 */
 void QGLFormat::setAlphaBufferSize(int size)
 {
+    detach();
     if (size < 0) {
         qWarning("QGLFormat::setAlphaBufferSize: Cannot set negative alpha buffer size %d", size);
         return;
@@ -918,6 +946,7 @@ int QGLFormat::alphaBufferSize() const
 */
 void QGLFormat::setAccumBufferSize(int size)
 {
+    detach();
     if (size < 0) {
         qWarning("QGLFormat::setAccumBufferSize: Cannot set negative accumulate buffer size %d", size);
         return;
@@ -942,6 +971,7 @@ int QGLFormat::accumBufferSize() const
 */
 void QGLFormat::setStencilBufferSize(int size)
 {
+    detach();
     if (size < 0) {
         qWarning("QGLFormat::setStencilBufferSize: Cannot set negative stencil buffer size %d", size);
         return;
diff --git a/src/opengl/qgl.h b/src/opengl/qgl.h
index 89f1676..0d72469 100644
--- a/src/opengl/qgl.h
+++ b/src/opengl/qgl.h
@@ -255,6 +255,8 @@ public:
 private:
     QGLFormatPrivate *d;
 
+    void detach();
+
     friend Q_OPENGL_EXPORT bool operator==(const QGLFormat&, const QGLFormat&);
     friend Q_OPENGL_EXPORT bool operator!=(const QGLFormat&, const QGLFormat&);
 };
@@ -277,7 +279,6 @@ public:
     bool isSharing() const;
     void reset();
 
-    // ### Qt 5: make format() return a const ref instead
     QGLFormat format() const;
     QGLFormat requestedFormat() const;
     void setFormat(const QGLFormat& format);
@@ -443,7 +444,6 @@ public:
     bool doubleBuffer() const;
     void swapBuffers();
 
-    // ### Qt 5: make format() return a const ref instead
     QGLFormat format() const;
     void setFormat(const QGLFormat& format);
 
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index 72ec35e..d4b7597 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -59,6 +59,7 @@
 #include "QtCore/qthread.h"
 #include "QtCore/qthreadstorage.h"
 #include "QtCore/qhash.h"
+#include "QtCore/qatomic.h"
 #include "private/qwidget_p.h"
 #include "qcache.h"
 
@@ -127,7 +128,9 @@ QT_END_INCLUDE_NAMESPACE
 class QGLFormatPrivate
 {
 public:
-    QGLFormatPrivate() {
+    QGLFormatPrivate()
+        : ref(1)
+    {
         opts = QGL::DoubleBuffer | QGL::DepthBuffer | QGL::Rgba | QGL::DirectRendering | QGL::StencilBuffer;
 #if defined(QT_OPENGL_ES_2)
         opts |= QGL::SampleBuffers;
@@ -137,6 +140,22 @@ public:
         numSamples = -1;
         swapInterval = -1;
     }
+    QGLFormatPrivate(const QGLFormatPrivate *other)
+        : ref(1),
+          opts(other->opts),
+          pln(other->pln),
+          depthSize(other->depthSize),
+          accumSize(other->accumSize),
+          stencilSize(other->stencilSize),
+          redSize(other->redSize),
+          greenSize(other->greenSize),
+          blueSize(other->blueSize),
+          alphaSize(other->alphaSize),
+          numSamples(other->numSamples),
+          swapInterval(other->swapInterval)
+    {
+    }
+    QAtomicInt ref;
     QGL::FormatOptions opts;
     int pln;
     int depthSize;