The fastDraw example

fastDraw

The fastDraw() function enables interactivity even with large scenes.

This example demonstrates the use of the fastDraw() function, which is called when the camera is manipulated. This function can be used to display a simplified version of the scene and is usefull for displaying very complex scene, while keeping an interactive camera motion.

fastDraw.h

#include <QGLViewer/qglviewer.h>

class Viewer : public QGLViewer
{
protected:
  virtual void init();
  virtual void draw();
  virtual void fastDraw();
  virtual QString helpString() const;
};

fastDraw.cpp

#include "fastDraw.h"

using namespace std;
using namespace qglviewer;

void Viewer::init()
{
  // Increase the material shininess, so that the difference between
  // the two versions of the spiral is more visible.
  glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 50.0);
  GLfloat specular_color[4] = { 0.8f, 0.8f, 0.8f, 1.0 };
  glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR,  specular_color);

  restoreStateFromFile();
  help();
}

static void drawSpiral(bool simplified = false)
{
  int nbSteps = 600;
  int nbSub = 50;
  if (simplified)
    {
      nbSteps = 60;
      nbSub = 2;
    }

  for (float n=0; n<nbSub; ++n)
    {
      glBegin(GL_QUAD_STRIP);
      for (float i=0.0; i<nbSteps; ++i)
	{
	  float ratio = i/nbSteps;
	  float angle = 21.0*ratio;
	  float radius = 1.0 - 0.5*ratio;

	  Vec center(radius*cos(angle), ratio-0.5, radius*sin(angle));

	  for (unsigned short j=0; j<2; ++j)
	    {
	      float delta = 3.0*(n+j)/nbSub;
	      Vec shift(cos(angle)*cos(delta), sin(delta), sin(angle)*cos(delta));

	      glColor3f(1-ratio, (n+j)/nbSub , ratio);
	      glNormal3fv(shift);
	      glVertex3fv(center+0.2f*shift);
	    }
	}
      glEnd();
    }
}

void Viewer::draw()
{
  drawSpiral();
}

void Viewer::fastDraw()
{
  drawSpiral(true);
}

QString Viewer::helpString() const
{
  QString text("<h2>F a s t D r a w</h2>");
  text += "The <code>fastDraw()</code> function is called instead of <code>draw()</code> when the camera ";
  text += "is manipulated. Providing such a simplified version of <code>draw()</code> allows for interactive ";
  text += "frame rates when the camera is moved, even for very complex scenes.";
  return text;
}

main.cpp

#include "fastDraw.h"
#include <qapplication.h>

int main(int argc, char** argv)
{
  QApplication application(argc,argv);

  Viewer viewer;

  viewer.setWindowTitle("fastDraw");

  viewer.show();

  return application.exec();
}

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