The cameraLight example

cameraLight

This example shows how to position a GL_LIGHT on the camera.

A spot light position and direction are set so that they always match the camera's current setup.

This is done using the camera->position() and camera->viewDirection() methods which return values expressed in the world coordinates system.

cameraLight.h

#include <QGLViewer/qglviewer.h>

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

private :
  virtual void drawSpiral();
};

cameraLight.cpp

#include "cameraLight.h"

using namespace std;
using namespace qglviewer;

void Viewer::draw()
{
	// Place light at camera position
	const Vec cameraPos = camera()->position();
	const GLfloat pos[4] = {(float)cameraPos[0], (float)cameraPos[1], (float)cameraPos[2], 1.0f};
	glLightfv(GL_LIGHT1, GL_POSITION, pos);

	// Orientate light along view direction
	glLightfv(GL_LIGHT1, GL_SPOT_DIRECTION, camera()->viewDirection());

	drawSpiral();
}

// Draws a spiral
void Viewer::drawSpiral()
{
	const float nbSteps = 1000.0;

	glBegin(GL_QUAD_STRIP);
	for (int i=0; i<nbSteps; ++i)
	{
		const float ratio = i/nbSteps;
		const float angle = 21.0*ratio;
		const float c = cos(angle);
		const float s = sin(angle);
		const float r1 = 1.0 - 0.8f*ratio;
		const float r2 = 0.8f - 0.8f*ratio;
		const float alt = ratio - 0.5f;
		const float nor = 0.5f;
		const float up = sqrt(1.0-nor*nor);
		glColor3f(1.0-ratio, 0.2f , ratio);
		glNormal3f(nor*c, up, nor*s);
		glVertex3f(r1*c, alt, r1*s);
		glVertex3f(r2*c, alt+0.05f, r2*s);
	}
	glEnd();
}

void Viewer::init()
{
	// Light setup
	glDisable(GL_LIGHT0);
	glEnable(GL_LIGHT1);

	// Light default parameters
	const GLfloat light_ambient[4]  = {1.0, 1.0, 1.0, 1.0};
	const GLfloat light_specular[4] = {1.0, 1.0, 1.0, 1.0};
	const GLfloat light_diffuse[4]  = {1.0, 1.0, 1.0, 1.0};

	glLightf( GL_LIGHT1, GL_SPOT_EXPONENT, 3.0);
	glLightf( GL_LIGHT1, GL_SPOT_CUTOFF,   10.0);
	glLightf( GL_LIGHT1, GL_CONSTANT_ATTENUATION,  0.1f);
	glLightf( GL_LIGHT1, GL_LINEAR_ATTENUATION,    0.3f);
	glLightf( GL_LIGHT1, GL_QUADRATIC_ATTENUATION, 0.3f);
	glLightfv(GL_LIGHT1, GL_AMBIENT,  light_ambient);
	glLightfv(GL_LIGHT1, GL_SPECULAR, light_specular);
	glLightfv(GL_LIGHT1, GL_DIFFUSE,  light_diffuse);

	// Restore previous viewer state.
	restoreStateFromFile();

	// Opens help window
	help();
}

QString Viewer::helpString() const
{
	QString text("<h2>C a m e r a L i g h t</h2>");
	text += "See the <b>Mouse</b> tab and the documentation web pages for details.<br><br>";
	text += "Press <b>Escape</b> to exit the viewer.";
	return text;
}

main.cpp

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

int main(int argc, char** argv)
{
  // Read command lines arguments.
  QApplication application(argc,argv);

  // Instantiate the viewer.
  Viewer viewer;

  viewer.setWindowTitle("cameraLight");

  // Make the viewer window visible on screen.
  viewer.show();

  // Run main loop.
  return application.exec();
}

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