Move resetOpenGLState out of QQFBO

QQFBO is not the only client of resetOpenGLState. Although in theory
third-party GL code that integrates with QtQuick should reset its
state, in practice it doesn't. By making resetOpenGLState
only available into QQFBO, now we're blocking a Qt5->6 upgrade path.

There's also no compelling reason for this function to be in QQFBO
at all, so move it out to as a free function in a ad-hoc new namespace.

Change-Id: Ic8e5c7e244db37a5b6257d516e6aea3a9db44898
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

7 files changed, 202 insertions, 82 deletions

diff --git a/src/quick/CMakeLists.txt b/src/quick/CMakeLists.txt
index 07a9927250..3fc9110d0c 100644
--- a/src/quick/CMakeLists.txt
+++ b/src/quick/CMakeLists.txt
@@ -484,6 +484,7 @@ qt_extend_target(Quick CONDITION QT_FEATURE_quick_shadereffect
 qt_extend_target(Quick CONDITION QT_FEATURE_opengl OR QT_FEATURE_opengles2 OR QT_FEATURE_opengles3
     SOURCES
         items/qquickframebufferobject.cpp items/qquickframebufferobject.h
+        util/qquickopenglutils.cpp util/qquickopenglutils.h
 )
 
 qt_extend_target(Quick CONDITION QT_FEATURE_quick_canvas
diff --git a/src/quick/items/qquickframebufferobject.cpp b/src/quick/items/qquickframebufferobject.cpp
index 66fa8818c0..03de94756d 100644
--- a/src/quick/items/qquickframebufferobject.cpp
+++ b/src/quick/items/qquickframebufferobject.cpp
@@ -41,7 +41,6 @@
 
 #include <QOpenGLFramebufferObject>
 #include <QOpenGLFunctions>
-#include <private/qopenglvertexarrayobject_p.h>
 #include <private/qquickitem_p.h>
 #include <private/qsgadaptationlayer_p.h>
 #include <qsgtextureprovider.h>
@@ -49,6 +48,7 @@
 
 #include <QSGSimpleTextureNode>
 #include <QSGRendererInterface>
+#include <QQuickOpenGLUtils>
 
 QT_BEGIN_NAMESPACE
 
@@ -209,7 +209,6 @@ public:
         , renderPending(true)
         , invalidatePending(false)
         , devicePixelRatio(1)
-        , vaoHelper(nullptr)
     {
         qsgnode_set_description(this, QStringLiteral("fbonode"));
     }
@@ -220,7 +219,6 @@ public:
         delete texture();
         delete fbo;
         delete msDisplayFbo;
-        delete vaoHelper;
     }
 
     void scheduleRender()
@@ -241,7 +239,7 @@ public Q_SLOTS:
             renderPending = false;
 
             window->beginExternalCommands();
-            renderer->resetOpenGLState();
+            QQuickOpenGLUtils::resetOpenGLState();
 
             fbo->bind();
             QOpenGLContext::currentContext()->functions()->glViewport(0, 0, fbo->width(), fbo->height());
@@ -277,7 +275,6 @@ public:
     bool invalidatePending;
 
     qreal devicePixelRatio;
-    QOpenGLVertexArrayObjectHelper *vaoHelper;
 };
 
 static inline bool isOpenGL(QSGRenderContext *rc)
@@ -477,7 +474,7 @@ QOpenGLFramebufferObject *QQuickFramebufferObject::Renderer::framebufferObject()
  * context. This means that the state might have been modified by Quick before
  * invoking this function.
  *
- * \note It is recommended to call resetOpenGLState() before
+ * \note It is recommended to call QQuickOpenGLUtils::resetOpenGLState() before
  * returning. This resets OpenGL state used by the Qt Quick renderer and thus
  * avoids interference from the state changes made by the rendering code in this
  * function.
@@ -553,77 +550,6 @@ void QQuickFramebufferObject::Renderer::update()
         ((QSGFramebufferObjectNode *) data)->scheduleRender();
 }
 
-/*!
-    Call this function to reset the OpenGL context its default state.
-
-    The scene graph uses the OpenGL context and will both rely on and
-    clobber its state. When mixing raw OpenGL commands with scene
-    graph rendering, this function provides a convenient way of
-    resetting the OpenGL context state back to its default values.
-
-    This function does not touch state in the fixed-function pipeline.
-
-    \warning This function will only reset the OpenGL context in
-    relation to what may be changed internally as part of the OpenGL
-    scene graph. It does not reset anything that has been changed
-    externally such as direct OpenGL calls done inside the application
-    code if those same calls are not used internally. (for example,
-    various OpenGL 3.x or 4.x specific state)
-
-    \since 6.0
- */
-void QQuickFramebufferObject::Renderer::resetOpenGLState()
-{
-    QOpenGLContext *ctx = QOpenGLContext::currentContext();
-    if (!ctx || !data)
-        return;
-
-    QOpenGLFunctions *gl = ctx->functions();
-
-    gl->glBindBuffer(GL_ARRAY_BUFFER, 0);
-    gl->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
-
-    QOpenGLVertexArrayObjectHelper *&vaoHelper(static_cast<QSGFramebufferObjectNode *>(data)->vaoHelper);
-    if (!vaoHelper)
-        vaoHelper = new QOpenGLVertexArrayObjectHelper(ctx);
-    if (vaoHelper->isValid())
-        vaoHelper->glBindVertexArray(0);
-
-    if (ctx->isOpenGLES() || (gl->openGLFeatures() & QOpenGLFunctions::FixedFunctionPipeline)) {
-        int maxAttribs;
-        gl->glGetIntegerv(GL_MAX_VERTEX_ATTRIBS, &maxAttribs);
-        for (int i=0; i<maxAttribs; ++i) {
-            gl->glVertexAttribPointer(i, 4, GL_FLOAT, GL_FALSE, 0, nullptr);
-            gl->glDisableVertexAttribArray(i);
-        }
-    }
-
-    gl->glActiveTexture(GL_TEXTURE0);
-    gl->glBindTexture(GL_TEXTURE_2D, 0);
-
-    gl->glDisable(GL_DEPTH_TEST);
-    gl->glDisable(GL_STENCIL_TEST);
-    gl->glDisable(GL_SCISSOR_TEST);
-
-    gl->glColorMask(true, true, true, true);
-    gl->glClearColor(0, 0, 0, 0);
-
-    gl->glDepthMask(true);
-    gl->glDepthFunc(GL_LESS);
-    gl->glClearDepthf(1);
-
-    gl->glStencilMask(0xff);
-    gl->glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
-    gl->glStencilFunc(GL_ALWAYS, 0, 0xff);
-
-    gl->glDisable(GL_BLEND);
-    gl->glBlendFunc(GL_ONE, GL_ZERO);
-
-    gl->glUseProgram(0);
-
-    QOpenGLFramebufferObject::bindDefault();
-}
-
 #include "qquickframebufferobject.moc"
 #include "moc_qquickframebufferobject.cpp"
 
diff --git a/src/quick/items/qquickframebufferobject.h b/src/quick/items/qquickframebufferobject.h
index e8aa4a24fb..4bb335c6ed 100644
--- a/src/quick/items/qquickframebufferobject.h
+++ b/src/quick/items/qquickframebufferobject.h
@@ -68,7 +68,6 @@ public:
         QOpenGLFramebufferObject *framebufferObject() const;
         void update();
         void invalidateFramebufferObject();
-        void resetOpenGLState();
     private:
         friend class QSGFramebufferObjectNode;
         friend class QQuickFramebufferObject;
diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index 523177b072..54926c3e9b 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -4970,7 +4970,7 @@ const QQuickWindow::GraphicsStateInfo &QQuickWindow::graphicsStateInfo()
     application, not retrieved from the scene graph). With graphics APIs where
     no native command buffer concept is exposed (OpenGL, Direct 3D 11),
     beginExternalCommands() and endExternalCommands() together provide a
-    replacement for the removed Qt 5 resetOpenGLState() function.
+    replacement for the Qt 5 resetOpenGLState() function.
 
     Calling this function and endExternalCommands() is not necessary within the
     \l{QSGRenderNode::render()}{render()} implementation of a QSGRenderNode
@@ -4992,7 +4992,7 @@ const QQuickWindow::GraphicsStateInfo &QQuickWindow::graphicsStateInfo()
     the OpenGL state in the context can have arbitrary settings, and this
     function does not perform any resetting of the state back to defaults.
 
-    \sa endExternalCommands()
+    \sa endExternalCommands(), QQuickOpenGLUtils::resetOpenGLState()
 
     \since 5.14
  */
@@ -5022,14 +5022,14 @@ void QQuickWindow::beginExternalCommands()
     application, not retrieved from the scene graph). With graphics APIs where
     no native command buffer concept is exposed (OpenGL, Direct 3D 11),
     beginExternalCommands() and endExternalCommands() together provide a
-    replacement for the removed Qt 5 resetOpenGLState() function.
+    replacement for the Qt 5 resetOpenGLState() function.
 
     Calling this function and beginExternalCommands() is not necessary within the
     \l{QSGRenderNode::render()}{render()} implementation of a QSGRenderNode
     because the scene graph performs the necessary steps implicitly for render
     nodes.
 
-    \sa beginExternalCommands()
+    \sa beginExternalCommands(), QQuickOpenGLUtils::resetOpenGLState()
 
     \since 5.14
  */
diff --git a/src/quick/util/qquickopenglutils.cpp b/src/quick/util/qquickopenglutils.cpp
new file mode 100644
index 0000000000..3a81e2dbd3
--- /dev/null
+++ b/src/quick/util/qquickopenglutils.cpp
@@ -0,0 +1,127 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQuick module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qquickopenglutils.h"
+
+#include <QOpenGLContext>
+#include <QOpenGLFunctions>
+#include <QOpenGLFramebufferObject>
+#include <private/qopenglvertexarrayobject_p.h>
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \namespace QQuickOpenGLUtils
+    \inmodule QtQuick
+    \since 6.0
+
+    \brief The QQuickOpenGLUtils namespace contains utilities for Qt
+    Quick when used with an OpenGL backend.
+*/
+
+/*!
+    Call this function to reset the current OpenGL context its default state.
+
+    The scene graph uses the OpenGL context and will both rely on and
+    clobber its state. When mixing raw OpenGL commands with scene
+    graph rendering, this function provides a convenient way of
+    resetting the OpenGL context state back to its default values.
+
+    This function does not touch state in the fixed-function pipeline.
+
+    \warning This function will only reset the OpenGL context in
+    relation to what may be changed internally as part of the OpenGL
+    scene graph. It does not reset anything that has been changed
+    externally such as direct OpenGL calls done inside the application
+    code if those same calls are not used internally (for example,
+    various OpenGL 3.x or 4.x specific state).
+
+    \since 6.0
+*/
+void QQuickOpenGLUtils::resetOpenGLState()
+{
+    QOpenGLContext *ctx = QOpenGLContext::currentContext();
+    if (!ctx)
+        return;
+
+    QOpenGLFunctions *gl = ctx->functions();
+
+    gl->glBindBuffer(GL_ARRAY_BUFFER, 0);
+    gl->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+
+    QOpenGLVertexArrayObjectHelper *vaoHelper = QOpenGLVertexArrayObjectHelper::vertexArrayObjectHelperForContext(ctx);
+    if (vaoHelper->isValid())
+        vaoHelper->glBindVertexArray(0);
+
+    if (ctx->isOpenGLES() || (gl->openGLFeatures() & QOpenGLFunctions::FixedFunctionPipeline)) {
+        int maxAttribs;
+        gl->glGetIntegerv(GL_MAX_VERTEX_ATTRIBS, &maxAttribs);
+        for (int i=0; i<maxAttribs; ++i) {
+            gl->glVertexAttribPointer(i, 4, GL_FLOAT, GL_FALSE, 0, nullptr);
+            gl->glDisableVertexAttribArray(i);
+        }
+    }
+
+    gl->glActiveTexture(GL_TEXTURE0);
+    gl->glBindTexture(GL_TEXTURE_2D, 0);
+
+    gl->glDisable(GL_DEPTH_TEST);
+    gl->glDisable(GL_STENCIL_TEST);
+    gl->glDisable(GL_SCISSOR_TEST);
+
+    gl->glColorMask(true, true, true, true);
+    gl->glClearColor(0, 0, 0, 0);
+
+    gl->glDepthMask(true);
+    gl->glDepthFunc(GL_LESS);
+    gl->glClearDepthf(1);
+
+    gl->glStencilMask(0xff);
+    gl->glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
+    gl->glStencilFunc(GL_ALWAYS, 0, 0xff);
+
+    gl->glDisable(GL_BLEND);
+    gl->glBlendFunc(GL_ONE, GL_ZERO);
+
+    gl->glUseProgram(0);
+
+    QOpenGLFramebufferObject::bindDefault();
+}
+
+QT_END_NAMESPACE
diff --git a/src/quick/util/qquickopenglutils.h b/src/quick/util/qquickopenglutils.h
new file mode 100644
index 0000000000..38e3f00c19
--- /dev/null
+++ b/src/quick/util/qquickopenglutils.h
@@ -0,0 +1,59 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQuick module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QQUICKOPENGLUTILS_H
+#define QQUICKOPENGLUTILS_H
+
+#if 0
+#pragma qt_class(QQuickOpenGLUtils)
+#endif
+
+#include <QtQuick/qtquickglobal.h>
+
+QT_BEGIN_NAMESPACE
+
+namespace QQuickOpenGLUtils {
+
+Q_QUICK_EXPORT void resetOpenGLState();
+
+} // namespace QQuickOpenGLUtils
+
+QT_END_NAMESPACE
+
+#endif // QQUICKOPENGLUTILS_H
diff --git a/src/quick/util/util.pri b/src/quick/util/util.pri
index f61a967959..56e7d342f8 100644
--- a/src/quick/util/util.pri
+++ b/src/quick/util/util.pri
@@ -80,3 +80,11 @@ qtConfig(quick-path) {
         $$PWD/qquickpath_p_p.h \
         $$PWD/qquickpathinterpolator_p.h
 }
+
+qtConfig(opengl(es1|es2)?) {
+    SOURCES += \
+        $$PWD/qquickopenglutils.cpp
+
+    HEADERS += \
+        $$PWD/qquickopenglutils.h
+}