beziercurve.cpp Example File

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 #include "beziercurve.h"

 #include <QtQuick/qsgnode.h>
 #include <QtQuick/qsgflatcolormaterial.h>

 BezierCurve::BezierCurve(QQuickItem *parent)
     : QQuickItem(parent)
     , m_p1(0, 0)
     , m_p2(1, 0)
     , m_p3(0, 1)
     , m_p4(1, 1)
     , m_segmentCount(32)
 {
     setFlag(ItemHasContents, true);
 }

 BezierCurve::~BezierCurve()
 {
 }

 void BezierCurve::setP1(const QPointF &p)
 {
     if (p == m_p1)
         return;

     m_p1 = p;
     emit p1Changed(p);
     update();
 }

 void BezierCurve::setP2(const QPointF &p)
 {
     if (p == m_p2)
         return;

     m_p2 = p;
     emit p2Changed(p);
     update();
 }

 void BezierCurve::setP3(const QPointF &p)
 {
     if (p == m_p3)
         return;

     m_p3 = p;
     emit p3Changed(p);
     update();
 }

 void BezierCurve::setP4(const QPointF &p)
 {
     if (p == m_p4)
         return;

     m_p4 = p;
     emit p4Changed(p);
     update();
 }

 void BezierCurve::setSegmentCount(int count)
 {
     if (m_segmentCount == count)
         return;

     m_segmentCount = count;
     emit segmentCountChanged(count);
     update();
 }

 QSGNode *BezierCurve::updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *)
 {
     QSGGeometryNode *node = nullptr;
     QSGGeometry *geometry = nullptr;

     if (!oldNode) {
         node = new QSGGeometryNode;
         geometry = new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), m_segmentCount);
         geometry->setLineWidth(2);
         geometry->setDrawingMode(QSGGeometry::DrawLineStrip);
         node->setGeometry(geometry);
         node->setFlag(QSGNode::OwnsGeometry);
         QSGFlatColorMaterial *material = new QSGFlatColorMaterial;
         material->setColor(QColor(255, 0, 0));
         node->setMaterial(material);
         node->setFlag(QSGNode::OwnsMaterial);
     } else {
         node = static_cast<QSGGeometryNode *>(oldNode);
         geometry = node->geometry();
         geometry->allocate(m_segmentCount);
     }

     QSizeF itemSize = size();
     QSGGeometry::Point2D *vertices = geometry->vertexDataAsPoint2D();
     for (int i = 0; i < m_segmentCount; ++i) {
         qreal t = i / qreal(m_segmentCount - 1);
         qreal invt = 1 - t;

         QPointF pos = invt * invt * invt * m_p1
                     + 3 * invt * invt * t * m_p2
                     + 3 * invt * t * t * m_p3
                     + t * t * t * m_p4;

         float x = pos.x() * itemSize.width();
         float y = pos.y() * itemSize.height();

         vertices[i].set(x, y);
     }
     node->markDirty(QSGNode::DirtyGeometry);

     return node;
 }