linenode.cpp Example File

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 #include "linenode.h"

 #include <QtGui/QColor>

 #include <QtQuick/QSGSimpleMaterial>

 struct LineMaterial
 {
     QColor color;
     float spread;
     float size;
 };

 class LineShader : public QSGSimpleMaterialShader<LineMaterial>
 {
     QSG_DECLARE_SIMPLE_SHADER(LineShader, LineMaterial)

 public:
     LineShader() {
         setShaderSourceFile(QOpenGLShader::Vertex, ":/scenegraph/graph/shaders/line.vsh");
         setShaderSourceFile(QOpenGLShader::Fragment, ":/scenegraph/graph/shaders/line.fsh");
     }

     QList<QByteArray> attributes() const override {  return QList<QByteArray>() << "pos" << "t"; }

     void updateState(const LineMaterial *m, const LineMaterial *) override {
         program()->setUniformValue(id_color, m->color);
         program()->setUniformValue(id_spread, m->spread);
         program()->setUniformValue(id_size, m->size);
     }

     void resolveUniforms() override {
         id_spread = program()->uniformLocation("spread");
         id_size = program()->uniformLocation("size");
         id_color = program()->uniformLocation("color");
     }

 private:
     int id_color = -1;
     int id_spread = -1;
     int id_size = -1;
 };

 struct LineVertex {
     float x;
     float y;
     float t;
     inline void set(float xx, float yy, float tt) { x = xx; y = yy; t = tt; }
 };

 static const QSGGeometry::AttributeSet &attributes()
 {
     static QSGGeometry::Attribute attr[] = {
         QSGGeometry::Attribute::create(0, 2, GL_FLOAT, true),
         QSGGeometry::Attribute::create(1, 1, GL_FLOAT)
     };
     static QSGGeometry::AttributeSet set = { 2, 3 * sizeof(float), attr };
     return set;
 }

 LineNode::LineNode(float size, float spread, const QColor &color)
     : m_geometry(attributes(), 0)
 {
     setGeometry(&m_geometry);
     m_geometry.setDrawingMode(GL_TRIANGLE_STRIP);

     QSGSimpleMaterial<LineMaterial> *m = LineShader::createMaterial();
     m->state()->color = color;
     m->state()->size = size;
     m->state()->spread = spread;
     m->setFlag(QSGMaterial::Blending);
     setMaterial(m);
     setFlag(OwnsMaterial);
 }

 /*
  * Assumes that samples have values in the range of 0 to 1 and scales them to
  * the height of bounds. The samples are stretched out horizontally along the
  * width of the bounds.
  *
  * The position of each pair of points is identical, but we use the third value
  * "t" to shift the point up or down and to add antialiasing.
  */
 void LineNode::updateGeometry(const QRectF &bounds, const QList<qreal> &samples)
 {
     m_geometry.allocate(samples.size() * 2);

     float x = bounds.x();
     float y = bounds.y();
     float w = bounds.width();
     float h = bounds.height();

     float dx = w / (samples.size() - 1);

     LineVertex *v = (LineVertex *) m_geometry.vertexData();
     for (int i=0; i<samples.size(); ++i) {
         v[i*2+0].set(x + dx * i, y + samples.at(i) * h, 0);
         v[i*2+1].set(x + dx * i, y + samples.at(i) * h, 1);
     }

     markDirty(QSGNode::DirtyGeometry);
 }