Improve performance of QStaticText on OpenGL by caching data on GPU

There's a big improvement to be seen in the OpenGL engine by caching
the vertex data for the QStaticText in VBOs. In order to have the
buffers properly disposed, I've implemented a userdata concept for
QStaticTextItem. By default, the optimizations will be turned off, and
can be turned on by using the useBackendOptimizations flag.

4 files changed, 91 insertions, 15 deletions

diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index 54eed03..521072f 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -5800,6 +5800,7 @@ void QPainter::drawStaticText(const QPointF &position, const QStaticText &static
                 textItem->glyphPositions[i].x += fx - oldX;
                 textItem->glyphPositions[i].y += fy - oldY;
             }
+            textItem->userDataNeedsUpdate = true;
         }
 
         staticText_d->position = transformedPosition;
diff --git a/src/gui/text/qstatictext.cpp b/src/gui/text/qstatictext.cpp
index 6c960bb..7be89cb 100644
--- a/src/gui/text/qstatictext.cpp
+++ b/src/gui/text/qstatictext.cpp
@@ -236,6 +236,43 @@ QString QStaticText::text() const
 }
 
 /*!
+  Sets whether the QStaticText object should use optimizations specific to the paint engine
+  backend if they are available. If \a on is set to true, backend optimizations will be turned
+  on, otherwise they will be turned off. The default value is false.
+
+  If backend optimizations are on, the paint engine used to draw the static text is allowed to
+  store data in the object which will assist it in future calls to drawStaticText. In particular,
+  when using the opengl graphics system, or when painting on a QGLWidget, turning this flag on will
+  improve performance, but increase the memory footprint of the QStaticText object.
+
+  The default value is false.
+
+  \note This function will cause the layout of the text to be recalculated.
+
+  \sa useBackendOptimizations()
+*/
+void QStaticText::setUseBackendOptimizations(bool on)
+{
+    if (on == d_ptr->useBackendOptimizations)
+        return;
+
+    detach();
+    d_ptr->useBackendOptimizations = on;
+    d_ptr->init();
+}
+
+/*!
+  Returns whether the QStaticText object should use optimizations specific to the paint engine
+  backend when possible. By default this setting is false.
+
+  \sa setUseBackendOptimizations()
+*/
+bool QStaticText::useBackendOptimizations() const
+{
+    return d_ptr->useBackendOptimizations;
+}
+
+/*!
     Sets the maximum size of the QStaticText to \a maximumSize.
 
     \note This function will cause the layout of the text to be recalculated.
@@ -470,6 +507,12 @@ void QStaticTextPrivate::init()
     itemCount = counterDevice.itemCount();    
     items = new QStaticTextItem[itemCount];
 
+    if (useBackendOptimizations) {
+        for (int i=0; i<itemCount; ++i)
+            items[i].useBackendOptimizations = true;
+    }
+
+
     int glyphCount = counterDevice.glyphCount();
     glyphPool = new glyph_t[glyphCount];
     positionPool = new QFixedPoint[glyphCount];
diff --git a/src/gui/text/qstatictext.h b/src/gui/text/qstatictext.h
index de2fdb3..d79d887 100644
--- a/src/gui/text/qstatictext.h
+++ b/src/gui/text/qstatictext.h
@@ -73,6 +73,9 @@ public:
 
     void prepare(const QTransform &matrix, const QFont &font);
 
+    void setUseBackendOptimizations(bool on);
+    bool useBackendOptimizations() const;
+
     QStaticText &operator=(const QStaticText &);
     bool operator==(const QStaticText &) const;
     bool operator!=(const QStaticText &) const;
diff --git a/src/gui/text/qstatictext_p.h b/src/gui/text/qstatictext_p.h
index 78f7896..bca59e0 100644
--- a/src/gui/text/qstatictext_p.h
+++ b/src/gui/text/qstatictext_p.h
@@ -57,10 +57,35 @@
 
 QT_BEGIN_NAMESPACE
 
+class QStaticTextUserData
+{
+public:
+    enum Type {
+        NoUserData,
+        OpenGLUserData
+    };
+
+    QStaticTextUserData(Type t) : type(t) {}
+    virtual ~QStaticTextUserData() {}
+
+    Type type;
+};
+
 class Q_GUI_EXPORT QStaticTextItem
 {
 public:    
-    QStaticTextItem() : chars(0), numChars(0), fontEngine(0) {}
+    QStaticTextItem() : chars(0), numChars(0), fontEngine(0), userData(0),
+                        useBackendOptimizations(false), userDataNeedsUpdate(0) {}
+    ~QStaticTextItem() { delete userData; }
+
+    void setUserData(QStaticTextUserData *newUserData)
+    {
+        if (userData == newUserData)
+            return;
+
+        delete userData;
+        userData = newUserData;
+    }
 
     QFixedPoint *glyphPositions;                 // 8 bytes per glyph
     glyph_t *glyphs;                             // 4 bytes per glyph
@@ -73,8 +98,11 @@ public:
     int numChars;                                // 4 bytes per item
     QFontEngine *fontEngine;                     // 4 bytes per item
     QFont font;                                  // 8 bytes per item
+    QStaticTextUserData *userData;               // 8 bytes per item
+    char useBackendOptimizations : 1;            // 1 byte per item
+    char userDataNeedsUpdate : 1;                //
                                                  // ================
-                                                 // 32 bytes per item
+                                                 // 41 bytes per item
 };
 
 class QStaticText;
@@ -86,22 +114,23 @@ public:
 
     void init();
 
-    QAtomicInt ref;            // 4 bytes per text
+    QAtomicInt ref;                      // 4 bytes per text
 
-    QString text;              // 4 bytes per text
-    QFont font;                // 8 bytes per text
-    QSizeF size;               // 16 bytes per text
-    QPointF position;          // 16 bytes per text
+    QString text;                        // 4 bytes per text
+    QFont font;                          // 8 bytes per text
+    QSizeF size;                         // 16 bytes per text
+    QPointF position;                    // 16 bytes per text
 
-    QTransform matrix;         // 80 bytes per text
-    QStaticTextItem *items;    // 4 bytes per text
-    int itemCount;             // 4 bytes per text
-    glyph_t *glyphPool;        // 4 bytes per text
-    QFixedPoint *positionPool; // 4 bytes per text
+    QTransform matrix;                   // 80 bytes per text
+    QStaticTextItem *items;              // 4 bytes per text
+    int itemCount;                       // 4 bytes per text
+    glyph_t *glyphPool;                  // 4 bytes per text
+    QFixedPoint *positionPool;           // 4 bytes per text
 
-    char needsClipRect : 1;    // 1 byte per text
-                               // ================
-                               // 145 bytes per text
+    char needsClipRect           : 1;    // 1 byte per text
+    char useBackendOptimizations : 1;
+                                         // ================
+                                         // 145 bytes per text
 
     static QStaticTextPrivate *get(const QStaticText *q);
 };