Copy QSGEngine functions to QQuickCanvas.

Long term we intend to remove the QSGEngine class
all together so this is the first step. It duplicates
some of the logic but doesn't break anything.

Also including an example on how to use it in
examples/declarative/openglunderqml

Change-Id: I69ed93ec5fa1b5c4c746169306d38f8d6ce80477
Reviewed-by: Gunnar Sletta <gunnar.sletta@nokia.com>

1 files changed, 123 insertions, 0 deletions

diff --git a/examples/declarative/openglunderqml/squircle.cpp b/examples/declarative/openglunderqml/squircle.cpp
new file mode 100644
index 0000000000..c2d4c0ac97
--- /dev/null
+++ b/examples/declarative/openglunderqml/squircle.cpp
@@ -0,0 +1,123 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the demonstration applications of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** This file may be used under the terms of the GNU Lesser General Public
+** License version 2.1 as published by the Free Software Foundation and
+** appearing in the file LICENSE.LGPL included in the packaging of this
+** file. Please review the following information to ensure the GNU Lesser
+** General Public License version 2.1 requirements will be met:
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights. These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU General
+** Public License version 3.0 as published by the Free Software Foundation
+** and appearing in the file LICENSE.GPL included in the packaging of this
+** file. Please review the following information to ensure the GNU General
+** Public License version 3.0 requirements will be met:
+** http://www.gnu.org/copyleft/gpl.html.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "squircle.h"
+
+#include <qsgengine.h>
+#include <qquickcanvas.h>
+#include <QOpenGLShaderProgram>
+
+Squircle::Squircle()
+    : m_program(0)
+{
+    setFlag(ItemHasContents);
+}
+
+void Squircle::itemChange(ItemChange change, const ItemChangeData &)
+{
+    // The ItemSceneChange event is sent when we are first attached to a canvas.
+    if (change == ItemSceneChange) {
+        QQuickCanvas *c = canvas();
+
+        // Connect our the beforeRendering signal to our paint function.
+        // Since this call is executed on the rendering thread it must be
+        // a Qt::DirectConnection
+        connect(c, SIGNAL(beforeRendering()), this, SLOT(paint()), Qt::DirectConnection);
+
+        // If we allow QML to do the clearing, they would clear what we paint
+        // and nothing would show.
+        c->setClearBeforeRendering(false);
+    }
+}
+
+
+void Squircle::paint()
+{
+    if (!m_program) {
+        m_program = new QOpenGLShaderProgram();
+        m_program->addShaderFromSourceCode(QOpenGLShader::Vertex,
+                                           "attribute highp vec4 vertices;"
+                                           "varying highp vec2 coords;"
+                                           "void main() {"
+                                           "    gl_Position = vertices;"
+                                           "    coords = vertices.xy;"
+                                           "}");
+        m_program->addShaderFromSourceCode(QOpenGLShader::Fragment,
+                                           "uniform lowp float t;"
+                                           "varying highp vec2 coords;"
+                                           "void main() {"
+                                           "    lowp float i = 1. - (pow(coords.x, 4.) + pow(coords.y, 4.));"
+                                           "    i = smoothstep(t - 0.3, t + 0.3, i);"
+                                           "    gl_FragColor = vec4(coords / 2. + .5, i, i);"
+                                           "}");
+
+        m_program->bindAttributeLocation("vertices", 0);
+        m_program->link();
+    }
+
+    m_program->bind();
+
+    m_program->enableAttributeArray(0);
+
+    float values[] = {
+        -1, -1,
+        1, -1,
+        -1, 1,
+        1, 1
+    };
+    m_program->setAttributeArray(0, GL_FLOAT, values, 2);
+    m_program->setUniformValue("t", (float) m_t);
+
+    glDisable(GL_DEPTH_TEST);
+
+    glClearColor(0, 0, 0, 1);
+    glClear(GL_COLOR_BUFFER_BIT);
+
+    glEnable(GL_BLEND);
+    glBlendFunc(GL_SRC_ALPHA, GL_ONE);
+
+    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+
+    m_program->disableAttributeArray(0);
+    m_program->release();
+}
+
+