examples: Add OpenGL under Qml example

This is example is based on the Qt's scene graph example
that uses and OpenGL animation inside Qml code.

Fixes: PYSIDE-1034
Change-Id: I012818d81d757571a711fcea68df51fa566ae5f9
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

7 files changed, 424 insertions, 0 deletions

diff --git a/examples/declarative/openglunderqml/doc/openglunderqml.rst b/examples/declarative/openglunderqml/doc/openglunderqml.rst
new file mode 100644
index 000000000..6a89a99d9
--- /dev/null
+++ b/examples/declarative/openglunderqml/doc/openglunderqml.rst
@@ -0,0 +1,21 @@
+OpenGL under QML Squircle
+=========================
+
+The OpenGL under QML example shows how an application can make use of the
+QQuickWindow::beforeRendering() signal to draw custom OpenGL content under a Qt
+Quick scene. This signal is emitted at the start of every frame, before the
+scene graph starts its rendering, thus any OpenGL draw calls that are made as
+a response to this signal, will stack under the Qt Quick items.
+
+As an alternative, applications that wish to render OpenGL content on top of
+the Qt Quick scene, can do so by connecting to the
+QQuickWindow::afterRendering() signal.
+
+In this example, we will also see how it is possible to have values that are
+exposed to QML which affect the OpenGL rendering. We animate the threshold
+value using a NumberAnimation in the QML file and this value is used by the
+OpenGL shader program that draws the squircles.
+
+.. image:: squircle.png
+   :width: 400
+   :alt: Squircle Screenshot
diff --git a/examples/declarative/openglunderqml/doc/squircle.png b/examples/declarative/openglunderqml/doc/squircle.png
new file mode 100644
index 000000000..c099a6b7e
--- /dev/null
+++ b/examples/declarative/openglunderqml/doc/squircle.png
diff --git a/examples/declarative/openglunderqml/main.py b/examples/declarative/openglunderqml/main.py
new file mode 100644
index 000000000..26e059f93
--- /dev/null
+++ b/examples/declarative/openglunderqml/main.py
@@ -0,0 +1,66 @@
+#############################################################################
+##
+## Copyright (C) 2021 The Qt Company Ltd.
+## Contact: http://www.qt.io/licensing/
+##
+## This file is part of the Qt for Python examples of the Qt Toolkit.
+##
+## $QT_BEGIN_LICENSE:BSD$
+## You may use this file under the terms of the BSD license as follows:
+##
+## "Redistribution and use in source and binary forms, with or without
+## modification, are permitted provided that the following conditions are
+## met:
+##   * Redistributions of source code must retain the above copyright
+##     notice, this list of conditions and the following disclaimer.
+##   * Redistributions in binary form must reproduce the above copyright
+##     notice, this list of conditions and the following disclaimer in
+##     the documentation and/or other materials provided with the
+##     distribution.
+##   * Neither the name of The Qt Company Ltd nor the names of its
+##     contributors may be used to endorse or promote products derived
+##     from this software without specific prior written permission.
+##
+##
+## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+## "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+## LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+## A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+## OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+## SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+## LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+## DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+## THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+## (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+##
+## $QT_END_LICENSE$
+##
+#############################################################################
+
+import sys
+from pathlib import Path
+
+from PySide6.QtCore import QUrl
+from PySide6.QtGui import QGuiApplication
+from PySide6.QtQml import qmlRegisterType
+from PySide6.QtQuick import QQuickView, QQuickWindow, QSGRendererInterface
+
+from squircle import Squircle
+
+if __name__ == "__main__":
+    app = QGuiApplication(sys.argv)
+
+    QQuickWindow.setGraphicsApi(QSGRendererInterface.OpenGLRhi)
+    qmlRegisterType(Squircle, "OpenGLUnderQML", 1, 0, "Squircle")
+
+    view = QQuickView()
+    view.setResizeMode(QQuickView.SizeRootObjectToView)
+    qml_file = Path(__file__).parent / "main.qml"
+    view.setSource(QUrl.fromLocalFile(qml_file))
+
+    if view.status() == QQuickView.Error:
+        sys.exit(-1)
+    view.show()
+
+    sys.exit(app.exec())
diff --git a/examples/declarative/openglunderqml/main.qml b/examples/declarative/openglunderqml/main.qml
new file mode 100644
index 000000000..7edcf523b
--- /dev/null
+++ b/examples/declarative/openglunderqml/main.qml
@@ -0,0 +1,86 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the demonstration applications of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick
+import OpenGLUnderQML
+
+Item {
+
+    width: 320
+    height: 480
+
+    Squircle {
+        SequentialAnimation on t {
+            NumberAnimation { to: 1; duration: 2500; easing.type: Easing.InQuad }
+            NumberAnimation { to: 0; duration: 2500; easing.type: Easing.OutQuad }
+            loops: Animation.Infinite
+            running: true
+        }
+    }
+    Rectangle {
+        color: Qt.rgba(1, 1, 1, 0.7)
+        radius: 10
+        border.width: 1
+        border.color: "white"
+        anchors.fill: label
+        anchors.margins: -10
+    }
+
+    Text {
+        id: label
+        color: "black"
+        wrapMode: Text.WordWrap
+        text: "The background here is a squircle rendered with raw OpenGL using the 'beforeRender()' signal in QQuickWindow. This text label and its border is rendered using QML"
+        anchors.right: parent.right
+        anchors.left: parent.left
+        anchors.bottom: parent.bottom
+        anchors.margins: 20
+    }
+}
diff --git a/examples/declarative/openglunderqml/openglunderqml.pyproject b/examples/declarative/openglunderqml/openglunderqml.pyproject
new file mode 100644
index 000000000..e7cfbc570
--- /dev/null
+++ b/examples/declarative/openglunderqml/openglunderqml.pyproject
@@ -0,0 +1,3 @@
+{
+    "files": [ "main.py", "main.qml", "squircle.py", "squirclerenderer.py"]
+}
diff --git a/examples/declarative/openglunderqml/squircle.py b/examples/declarative/openglunderqml/squircle.py
new file mode 100644
index 000000000..8d2cbca84
--- /dev/null
+++ b/examples/declarative/openglunderqml/squircle.py
@@ -0,0 +1,107 @@
+#############################################################################
+##
+## Copyright (C) 2021 The Qt Company Ltd.
+## Contact: http://www.qt.io/licensing/
+##
+## This file is part of the Qt for Python examples of the Qt Toolkit.
+##
+## $QT_BEGIN_LICENSE:BSD$
+## You may use this file under the terms of the BSD license as follows:
+##
+## "Redistribution and use in source and binary forms, with or without
+## modification, are permitted provided that the following conditions are
+## met:
+##   * Redistributions of source code must retain the above copyright
+##     notice, this list of conditions and the following disclaimer.
+##   * Redistributions in binary form must reproduce the above copyright
+##     notice, this list of conditions and the following disclaimer in
+##     the documentation and/or other materials provided with the
+##     distribution.
+##   * Neither the name of The Qt Company Ltd nor the names of its
+##     contributors may be used to endorse or promote products derived
+##     from this software without specific prior written permission.
+##
+##
+## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+## "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+## LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+## A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+## OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+## SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+## LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+## DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+## THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+## (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+##
+## $QT_END_LICENSE$
+##
+#############################################################################
+
+from PySide6.QtCore import Property, QRunnable, Qt, Signal, Slot
+from PySide6.QtQuick import QQuickItem, QQuickWindow
+
+from squirclerenderer import SquircleRenderer
+
+
+class CleanupJob(QRunnable):
+    def __init__(self, renderer):
+        super().__init__()
+        self._renderer = renderer
+
+    def run(self):
+        del self._renderer
+
+
+class Squircle(QQuickItem):
+
+    tChanged = Signal()
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        self._t = 0.0
+        self._renderer = None
+        self.windowChanged.connect(self.handleWindowChanged)
+
+    def t(self):
+        return self._t
+
+    def setT(self, value):
+        if self._t == value:
+            return
+        self._t = value
+        self.tChanged.emit()
+        if self.window():
+            self.window().update()
+
+    @Slot(QQuickWindow)
+    def handleWindowChanged(self, win):
+        if win:
+            win.beforeSynchronizing.connect(self.sync, type=Qt.DirectConnection)
+            win.sceneGraphInvalidated.connect(self.cleanup, type=Qt.DirectConnection)
+            win.setColor(Qt.black)
+            self.sync()
+
+    def cleanup(self):
+        del self._renderer
+        self._renderer = None
+
+    @Slot()
+    def sync(self):
+        if not self._renderer:
+            self._renderer = SquircleRenderer()
+            self.window().beforeRendering.connect(self._renderer.init, Qt.DirectConnection)
+            self.window().beforeRenderPassRecording.connect(
+                self._renderer.paint, Qt.DirectConnection
+            )
+        self._renderer.setViewportSize(self.window().size() * self.window().devicePixelRatio())
+        self._renderer.setT(self._t)
+        self._renderer.setWindow(self.window())
+
+    def releaseResources(self):
+        self.window().scheduleRenderJob(
+            CleanupJob(self._renderer), QQuickWindow.BeforeSynchronizingStage
+        )
+        self._renderer = None
+
+    t = Property(float, t, setT, notify=tChanged)
diff --git a/examples/declarative/openglunderqml/squirclerenderer.py b/examples/declarative/openglunderqml/squirclerenderer.py
new file mode 100644
index 000000000..12cd93bb8
--- /dev/null
+++ b/examples/declarative/openglunderqml/squirclerenderer.py
@@ -0,0 +1,141 @@
+#############################################################################
+##
+## Copyright (C) 2021 The Qt Company Ltd.
+## Contact: http://www.qt.io/licensing/
+##
+## This file is part of the Qt for Python examples of the Qt Toolkit.
+##
+## $QT_BEGIN_LICENSE:BSD$
+## You may use this file under the terms of the BSD license as follows:
+##
+## "Redistribution and use in source and binary forms, with or without
+## modification, are permitted provided that the following conditions are
+## met:
+##   * Redistributions of source code must retain the above copyright
+##     notice, this list of conditions and the following disclaimer.
+##   * Redistributions in binary form must reproduce the above copyright
+##     notice, this list of conditions and the following disclaimer in
+##     the documentation and/or other materials provided with the
+##     distribution.
+##   * Neither the name of The Qt Company Ltd nor the names of its
+##     contributors may be used to endorse or promote products derived
+##     from this software without specific prior written permission.
+##
+##
+## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+## "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+## LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+## A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+## OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+## SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+## LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+## DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+## THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+## (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+##
+## $QT_END_LICENSE$
+##
+#############################################################################
+
+from textwrap import dedent
+
+import numpy as np
+from OpenGL.GL import (GL_ARRAY_BUFFER, GL_BLEND, GL_DEPTH_TEST, GL_FLOAT,
+                       GL_ONE, GL_SRC_ALPHA, GL_TRIANGLE_STRIP)
+from PySide6.QtCore import QSize, Slot
+from PySide6.QtGui import QOpenGLFunctions
+from PySide6.QtOpenGL import (QOpenGLShader, QOpenGLShaderProgram,
+                              QOpenGLVersionProfile)
+from PySide6.QtQuick import QQuickWindow, QSGRendererInterface
+
+VERTEX_SHADER = dedent(
+    """\
+    attribute highp vec4 vertices;
+    varying highp vec2 coords;
+    void main() {
+        gl_Position = vertices;
+        coords = vertices.xy;
+    }
+    """
+)
+FRAGMENT_SHADER = dedent(
+    """\
+    uniform lowp float t;
+    varying highp vec2 coords;
+    void main() {
+        lowp float i = 1. - (pow(abs(coords.x), 4.) + pow(abs(coords.y), 4.));
+        i = smoothstep(t - 0.8, t + 0.8, i);
+        i = floor(i * 20.) / 20.;
+        gl_FragColor = vec4(coords * .5 + .5, i, i);
+    }
+    """
+)
+
+
+class SquircleRenderer(QOpenGLFunctions):
+    def __init__(self):
+        QOpenGLFunctions.__init__(self)
+        self._viewport_size = QSize()
+        self._t = 0.0
+        self._program = None
+        self._window = QQuickWindow()
+        self.profile = QOpenGLVersionProfile()
+        self.gl = None
+
+    def setT(self, t):
+        self._t = t
+
+    def setViewportSize(self, size):
+        self._viewport_size = size
+
+    def setWindow(self, window):
+        self._window = window
+
+    @Slot()
+    def init(self):
+        if not self._program:
+            rif = self._window.rendererInterface()
+            assert (
+                rif.graphicsApi() == QSGRendererInterface.OpenGL
+                or rif.graphicsApi() == QSGRendererInterface.OpenGLRhy
+            )
+            self.initializeOpenGLFunctions()
+            self._program = QOpenGLShaderProgram()
+            self._program.addCacheableShaderFromSourceCode(QOpenGLShader.Vertex, VERTEX_SHADER)
+            self._program.addCacheableShaderFromSourceCode(QOpenGLShader.Fragment, FRAGMENT_SHADER)
+            self._program.bindAttributeLocation("vertices", 0)
+            self._program.link()
+
+    @Slot()
+    def paint(self):
+        # Play nice with the RHI. Not strictly needed when the scenegraph uses
+        # OpenGL directly.
+        self._window.beginExternalCommands()
+
+        self._program.bind()
+
+        self._program.enableAttributeArray(0)
+
+        values = np.array([-1, -1, 1, -1, -1, 1, 1, 1], dtype="single")
+
+        # This example relies on (deprecated) client-side pointers for the vertex
+        # input. Therefore, we have to make sure no vertex buffer is bound.
+        self.glBindBuffer(GL_ARRAY_BUFFER, 0)
+
+        self._program.setAttributeArray(0, GL_FLOAT, values, 2)
+        self._program.setUniformValue1f("t", self._t)
+
+        self.glViewport(0, 0, self._viewport_size.width(), self._viewport_size.height())
+
+        self.glDisable(GL_DEPTH_TEST)
+
+        self.glEnable(GL_BLEND)
+        self.glBlendFunc(GL_SRC_ALPHA, GL_ONE)
+
+        self.glDrawArrays(GL_TRIANGLE_STRIP, 0, 4)
+
+        self._program.disableAttributeArray(0)
+        self._program.release()
+
+        self._window.endExternalCommands()