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;
}