Scene Graph - Custom Geometry¶
The custom geometry example shows how to create a QQuickItem which uses the scene graph API to build a custom geometry for the scene graph. It does this by creating a BezierCurve item which is made part of the CustomGeometry module and makes use of this in a QML file.
# Copyright (C) 2022 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
from __future__ import annotations
"""PySide6 port of the Qt Quick customgeometry example from Qt v6.x"""
import sys
from pathlib import Path
from PySide6.QtQuick import (QQuickView, QQuickItem, QSGNode, QSGGeometryNode,
QSGGeometry, QSGFlatColorMaterial)
from PySide6.QtQml import QmlElement
from PySide6.QtGui import QGuiApplication, QColor
from PySide6.QtCore import (QPointF, QUrl, Property, Signal, Slot)
# To be used on the @QmlElement decorator
# (QML_IMPORT_MINOR_VERSION is optional)
QML_IMPORT_NAME = "CustomGeometry"
QML_IMPORT_MAJOR_VERSION = 1
@QmlElement
class BezierCurve(QQuickItem):
p1Changed = Signal()
p2Changed = Signal()
p3Changed = Signal()
p4Changed = Signal()
segmentCountChanged = Signal()
def __init__(self, parent=None):
super().__init__(parent)
self._p1 = QPointF(0, 0)
self._p2 = QPointF(1, 0)
self._p3 = QPointF(0, 1)
self._p4 = QPointF(1, 1)
self._segmentCount = 32
self._node = None
self._geometry = None
self.setFlag(QQuickItem.Flags.ItemHasContents, True)
def p1(self):
return self._p1
def p2(self):
return self._p2
def p3(self):
return self._p3
def p4(self):
return self._p4
def segmentCount(self):
return self._segmentCount
@Slot(QPointF)
def setP1(self, p):
if p != self._p1:
self._p1 = p
self.p1Changed.emit()
self.update()
@Slot(QPointF)
def setP2(self, p):
if p != self._p2:
self._p2 = p
self.p2Changed.emit()
self.update()
@Slot(QPointF)
def setP3(self, p):
if p != self._p3:
self._p3 = p
self.p3Changed.emit()
self.update()
@Slot(QPointF)
def setP4(self, p):
if p != self._p4:
self._p4 = p
self.p4Changed.emit()
self.update()
@Slot(int)
def setSegmentCount(self, p):
if p != self._segmentCount:
self._segmentCount = p
self.segmentCountChanged.emit()
self.update()
def updatePaintNode(self, oldNode, updatePaintNodeData):
self._node = oldNode
if not self._node:
self._default_attributes = QSGGeometry.defaultAttributes_Point2D()
self._geometry = QSGGeometry(self._default_attributes, self._segmentCount)
self._geometry.setLineWidth(2)
self._geometry.setDrawingMode(QSGGeometry.DrawingMode.DrawLineStrip)
self._node = QSGGeometryNode()
self._node.setGeometry(self._geometry)
self._node.setFlag(QSGNode.Flags.OwnsGeometry)
self._material = QSGFlatColorMaterial()
self._material.setColor(QColor(255, 0, 0))
self._node.setMaterial(self._material)
self._node.setFlag(QSGNode.Flags.OwnsMaterial)
else:
self._geometry = self._node.geometry()
self._geometry.allocate(self._segmentCount)
item_size = self.size()
item_width = float(item_size.width())
item_height = float(item_size.height())
vertices = self._geometry.vertexDataAsPoint2D()
for i in range(self._segmentCount):
t = float(i) / float(self._segmentCount - 1)
inv_t = 1 - t
pos = ((inv_t * inv_t * inv_t * self._p1)
+ (3 * inv_t * inv_t * t * self._p2)
+ (3 * inv_t * t * t * self._p3)
+ (t * t * t * self._p4))
vertices[i].set(pos.x() * item_width, pos.y() * item_height)
self._geometry.setVertexDataAsPoint2D(vertices)
self._node.markDirty(QSGNode.DirtyGeometry)
return self._node
p1 = Property(QPointF, p1, setP1, notify=p1Changed)
p2 = Property(QPointF, p2, setP2, notify=p2Changed)
p3 = Property(QPointF, p3, setP3, notify=p3Changed)
p4 = Property(QPointF, p4, setP4, notify=p4Changed)
segmentCount = Property(int, segmentCount, setSegmentCount,
notify=segmentCountChanged)
if __name__ == "__main__":
app = QGuiApplication([])
view = QQuickView()
format = view.format()
format.setSamples(16)
view.setFormat(format)
qml_file = Path(__file__).parent / "main.qml"
view.setSource(QUrl.fromLocalFile(qml_file))
if not view.rootObject():
sys.exit(-1)
view.show()
ex = app.exec()
del view
sys.exit(ex)
// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
import QtQuick
import CustomGeometry
Item {
width: 300
height: 200
BezierCurve {
id: line
anchors.fill: parent
anchors.margins: 20
property real t
SequentialAnimation on t {
NumberAnimation { to: 1; duration: 2000; easing.type: Easing.InOutQuad }
NumberAnimation { to: 0; duration: 2000; easing.type: Easing.InOutQuad }
loops: Animation.Infinite
}
p2: Qt.point(t, 1 - t)
p3: Qt.point(1 - t, t)
}
Text {
anchors.bottom: line.bottom
x: 20
width: parent.width - 40
wrapMode: Text.WordWrap
text: "This curve is a custom scene graph item, implemented using GL_LINE_STRIP"
}
}