gridnode.cpp Example File

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 #include "gridnode.h"

 #include "qmath.h"

 #define GRID_SIZE 32

 GridNode::GridNode()
     : m_geometry(QSGGeometry::defaultAttributes_Point2D(), 0)
 {
     setGeometry(&m_geometry);
     m_geometry.setDrawingMode(GL_LINES);

     setMaterial(&m_material);
     m_material.setColor(Qt::gray);
 }

 /*
  * The function hardcodes a fixed set of grid lines and scales
  * those to the bounding rect.
  */
 void GridNode::setRect(const QRectF &rect)
 {
     int vCount = int((rect.width() - 1) / GRID_SIZE);
     int hCount = int((rect.height() - 1) / GRID_SIZE);

     int lineCount = vCount + hCount;

     QSGGeometry *g = geometry();

     g->allocate(lineCount * 2);

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

     QSGGeometry::Point2D *v = g->vertexDataAsPoint2D();

     // Then write the vertical lines
     for (int i=0; i<vCount; ++i)  {
         float dx = (i + 1) * GRID_SIZE;
         v[i*2].set(dx, y);
         v[i*2+1].set(dx, y + h);
     }
     v += vCount * 2;
     // Then write the horizontal lines
     for (int i=0; i<hCount; ++i)  {
         float dy = (i + 1) * GRID_SIZE;
         v[i*2].set(x, dy);
         v[i*2+1].set(x + w, dy);
     }

     // Tell the scenegraph we updated the geometry..
     markDirty(QSGNode::DirtyGeometry);
 }