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>

3 files changed, 194 insertions, 0 deletions

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
+}