graph.cpp Example File

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 #include "graph.h"

 #include "noisynode.h"
 #include "gridnode.h"
 #include "linenode.h"

 Graph::Graph()
     : m_samplesChanged(false)
     , m_geometryChanged(false)
 {
     setFlag(ItemHasContents, true);
 }

 void Graph::appendSample(qreal value)
 {
     m_samples << value;
     m_samplesChanged = true;
     update();
 }

 void Graph::removeFirstSample()
 {
     m_samples.removeFirst();
     m_samplesChanged = true;
     update();
 }

 void Graph::geometryChanged(const QRectF &newGeometry, const QRectF &oldGeometry)
 {
     m_geometryChanged = true;
     update();
     QQuickItem::geometryChanged(newGeometry, oldGeometry);
 }

 class GraphNode : public QSGNode
 {
 public:
     NoisyNode *background;
     GridNode *grid;
     LineNode *line;
     LineNode *shadow;
 };

 QSGNode *Graph::updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *)
 {
     GraphNode *n= static_cast<GraphNode *>(oldNode);

     QRectF rect = boundingRect();

     if (rect.isEmpty()) {
         delete n;
         return nullptr;
     }

     if (!n) {
         n = new GraphNode();

         n->background = new NoisyNode(window());
         n->grid = new GridNode();
         n->line = new LineNode(10, 0.5, QColor("steelblue"));
         n->shadow = new LineNode(20, 0.2f, QColor::fromRgbF(0.2, 0.2, 0.2, 0.4));

         n->appendChildNode(n->background);
         n->appendChildNode(n->grid);
         n->appendChildNode(n->shadow);
         n->appendChildNode(n->line);
     }

     if (m_geometryChanged) {
         n->background->setRect(rect);
         n->grid->setRect(rect);
     }

     if (m_geometryChanged || m_samplesChanged) {
         n->line->updateGeometry(rect, m_samples);
         // We don't need to calculate the geometry twice, so just steal it from the other one...
         n->shadow->setGeometry(n->line->geometry());
     }

     m_geometryChanged = false;
     m_samplesChanged = false;

     return n;
 }