Made GL2 engine default for QGLWidget, and added GL2 sync() function

To allow mixing QPainter and raw OpenGL commands we need to have some
way for the user to say that's he's about to use raw OpenGL so that we
are free to do buffering optimizations in the paint engines and use
either GL1 or GL2 paint engine. As there's already a syncState()
function in QPaintEngine we've reused this and added
QPaintEngineEx::sync() which takes care of syncing/flushing the paint
engine.

Reviewed-by: Trond

6 files changed, 50 insertions, 1 deletions

diff --git a/dist/changes-4.6.0 b/dist/changes-4.6.0
index 6a94f26..bedf58a 100644
--- a/dist/changes-4.6.0
+++ b/dist/changes-4.6.0
@@ -49,3 +49,8 @@ information about a particular change.
  - QStyleOptionGraphicsItem::levelOfDetails is obsoleted and its value
    is always initialized to 1. For a more fine-grained value use
    QStyleOptionGraphicsItem::levelOfDetailFromTransform(const QTransform &).
+
+ - When mixing OpenGL and QPainter calls you need to first call syncState()
+   on the paint engine, for example "painter->paintEngine()->syncState()".
+   This is to ensure that the engine flushes any pending drawing and sets up
+   the GL modelview/projection matrices properly.
diff --git a/src/gui/painting/qpaintengine.cpp b/src/gui/painting/qpaintengine.cpp
index 7de1ec4..9859425 100644
--- a/src/gui/painting/qpaintengine.cpp
+++ b/src/gui/painting/qpaintengine.cpp
@@ -49,6 +49,7 @@
 #include <private/qtextengine_p.h>
 #include <qvarlengtharray.h>
 #include <private/qfontengine_p.h>
+#include <private/qpaintengineex_p.h>
 
 
 QT_BEGIN_NAMESPACE
@@ -302,6 +303,9 @@ void QPaintEngine::syncState()
 {
     Q_ASSERT(state);
     updateState(*state);
+
+    if (isExtended())
+        static_cast<QPaintEngineEx *>(this)->sync();
 }
 
 static QPaintEngine *qt_polygon_recursion = 0;
diff --git a/src/gui/painting/qpaintengineex_p.h b/src/gui/painting/qpaintengineex_p.h
index 593726c..1c55242 100644
--- a/src/gui/painting/qpaintengineex_p.h
+++ b/src/gui/painting/qpaintengineex_p.h
@@ -216,6 +216,8 @@ public:
     inline QPainterState *state() { return static_cast<QPainterState *>(QPaintEngine::state); }
     inline const QPainterState *state() const { return static_cast<const QPainterState *>(QPaintEngine::state); }
 
+    virtual void sync() {}
+
     virtual QPixmapFilter *createPixmapFilter(int /*type*/) const { return 0; }
 
 protected:
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index e7b6ee4..40f3a8d 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
@@ -449,6 +449,43 @@ void QGL2PaintEngineExPrivate::drawTexture(const QGLRect& dest, const QGLRect& s
     glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
 }
 
+void QGL2PaintEngineEx::sync()
+{
+    Q_D(QGL2PaintEngineEx);
+    ensureActive();
+    d->transferMode(BrushDrawingMode);
+
+    QGLContext *ctx = d->ctx;
+    glUseProgram(0);
+
+#ifndef QT_OPENGL_ES_2
+    // be nice to people who mix OpenGL 1.x code with QPainter commands
+    // by setting modelview and projection matrices to mirror the GL 1
+    // paint engine
+    const QTransform& mtx = state()->matrix;
+
+    float mv_matrix[4][4] =
+    {
+        { mtx.m11(), mtx.m12(),     0, mtx.m13() },
+        { mtx.m21(), mtx.m22(),     0, mtx.m23() },
+        {         0,         0,     1,         0 },
+        {  mtx.dx(),  mtx.dy(),     0, mtx.m33() }
+    };
+
+    const QSize sz = d->drawable.size();
+
+    glMatrixMode(GL_PROJECTION);
+    glLoadIdentity();
+    glOrtho(0, sz.width(), sz.height(), 0, -999999, 999999);
+
+    glMatrixMode(GL_MODELVIEW);
+    glLoadMatrixf(&mv_matrix[0][0]);
+#endif
+
+    glDisable(GL_BLEND);
+    glActiveTexture(GL_TEXTURE0);
+}
+
 void QGL2PaintEngineExPrivate::transferMode(EngineMode newMode)
 {
     if (newMode == mode)
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h b/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
index dececa3..7213474 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
@@ -126,6 +126,7 @@ public:
         return static_cast<const QOpenGL2PaintEngineState *>(QPaintEngineEx::state());
     }
     void updateClipRegion(const QRegion &clipRegion, Qt::ClipOperation op);
+    virtual void sync();
 
 private:
     Q_DISABLE_COPY(QGL2PaintEngineEx)
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index b1a63b5..b3523d4 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -440,7 +440,7 @@ inline bool qt_gl_preferGL2Engine()
     return true;
 #else
     return (QGLFormat::openGLVersionFlags() & QGLFormat::OpenGL_Version_2_0)
-           && !qgetenv("QT_GL_USE_OPENGL2ENGINE").isEmpty();
+           && qgetenv("QT_GL_USE_OPENGL1ENGINE").isEmpty();
 #endif
 }