Quick lighting question

[Fahrenheit451]

Just learning about lighting and wondered if I was doing something wrong with my setup. I create three spotlights that shine onto a large gluSphere. Using gluLookAt I view the scene from up the Z axis, essentially from the front, and everything looks ok. I change the eye view point by decreasing the Z axis and essentialy "flip" the view when I hit the destination (origin in this case) of gluLookAt so I am viewing the rear of the sphere. Odd thing is that the spot lights are still shining on the back side of the sphere. It's as though the spehere is opaque.

Let me know if code/screenshots are required. Thanks.

[ce110ut]

yeah - could you please post some code [and screenies]?

we hope to help
:regards:

[Fahrenheit451]

Here is my init and draw scene routines:

int DrawGLScene()                                                                   
{ 
	// clear buffers
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
	glLoadIdentity();
 
	// setup camera view point
	gluLookAt(0.0f,2.0f,zoom,  0.0f,2.0f,0.0f,  0.0f,1.0f,0.0f);
 
	// update light positions
	glLightfv(GL_LIGHT1, GL_POSITION, lightPositionR);
	glLightfv(GL_LIGHT1, GL_SPOT_DIRECTION, lightDirectionR);
	glLightfv(GL_LIGHT2, GL_POSITION, lightPositionG);
	glLightfv(GL_LIGHT2, GL_SPOT_DIRECTION, lightDirectionG);
	glLightfv(GL_LIGHT3, GL_POSITION, lightPositionB);
	glLightfv(GL_LIGHT3, GL_SPOT_DIRECTION, lightDirectionB);
 
	// check key presses
	CheckKeyPress();
 
	// Draw ground at 0.0 Y axis
	DrawGround();
 
	// draw spot light positions and direction indicators
	DrawCrossHairs(lightPositionR[0],...
	DrawCrossHairs(lightPositionG[0],...
	DrawCrossHairs(lightPositionB[0],...
 
	// render and update particle fountain
	pMgr->Render();
	pMgr->Update(g_timer.timeStep);
 
	// draw sphere
	DrawSphere();
 
	// update fps in window title bar
	DisplayText();
 
	// update counters
	yrot += 0.05f;
	if (yrot > 359.0)
		yrot = 0.0f;
 
	return true;
} 
 
int InitGL(void)                                                                        
{
 
	yrot = 0.0f;
 
	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
	glClearDepth(1.0f);
 
	glShadeModel(GL_SMOOTH);
	glEnable(GL_DEPTH_TEST);
	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
 
	// load up our textures
	if (!LoadGLTexture(PARTICLE_TEXTURE1_FILE,...
 
	// Setup Particle Manager
	pMgr = new ParticleManager();
 
	// Create and setup new particle fountain
	fount[0] = new Fountain1;
	CreateFount();
 
	// enable and setp lighting and materials
	glEnable(GL_LIGHTING);
	// meterial properties
	glMaterialfv(GL_FRONT, GL_AMBIENT, matAmbient);
	glMaterialfv(GL_FRONT, GL_DIFFUSE, matDiffuse);
	glMaterialf(GL_FRONT, GL_SHININESS, 100.0f);
	// global ambient light
	glLightfv(GL_LIGHT0, GL_AMBIENT, ambientLight);
//	glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuseLight);
//	glLightfv(GL_LIGHT0, GL_SPECULAR, specularLight);
	glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);
 
	// red spot light
	glLightfv(GL_LIGHT1, GL_AMBIENT, ambientLightR);
	glLightfv(GL_LIGHT1, GL_DIFFUSE, diffuseLightR);
	glLightfv(GL_LIGHT1, GL_SPECULAR, specularLightR);
	glLightfv(GL_LIGHT1, GL_POSITION, lightPositionR);
	glLightf(GL_LIGHT1, GL_SPOT_CUTOFF, 5.0f);
	glLightf(GL_LIGHT1, GL_SPOT_EXPONENT, 100.0f);
		FVector p1, p2, p3;
		p1.Set(-1.0f, 2.0f, 20.0f);
		p2.Set(-5.0f, 2.0f, -2.0f);
		p3 = p2 - p1; p3.Normalize();
		lightDirectionR[0] = p3.x; lightDirectionR[1] = p3.y; lightDirectionR[2] = p3.z;
	glLightfv(GL_LIGHT1, GL_SPOT_DIRECTION, lightDirectionR);
 
	// green spot light
	glLightfv(GL_LIGHT2, GL_AMBIENT, ambientLightG);
	glLightfv(GL_LIGHT2, GL_DIFFUSE, diffuseLightG);
	glLightfv(GL_LIGHT2, GL_SPECULAR, specularLightG);
	glLightfv(GL_LIGHT2, GL_POSITION, lightPositionG);
	glLightf(GL_LIGHT2, GL_SPOT_CUTOFF, 5.0f);
	glLightf(GL_LIGHT2, GL_SPOT_EXPONENT, 100.0f);
		p1.Set(1.0f, 2.0f, 20.2f);
		p2.Set(5.0f, 2.0f, -2.0f);
		p3 = p2 - p1; p3.Normalize();
		lightDirectionG[0] = p3.x; lightDirectionG[1] = p3.y; lightDirectionG[2] = p3.z;
	glLightfv(GL_LIGHT2, GL_SPOT_DIRECTION, lightDirectionG);
 
	// blue spot light
	glLightfv(GL_LIGHT3, GL_AMBIENT, ambientLightB);
	glLightfv(GL_LIGHT3, GL_DIFFUSE, diffuseLightB);
	glLightfv(GL_LIGHT3, GL_SPECULAR, specularLightB);
	glLightfv(GL_LIGHT3, GL_POSITION, lightPositionB);
	glLightf(GL_LIGHT3, GL_SPOT_CUTOFF, 20.0f);
	glLightf(GL_LIGHT3, GL_SPOT_EXPONENT, 100.0f);
		p1.Set(0.0f, 0.0f, 6.0f);
		p2.Set(0.0f, 5.0f, -2.0f);
		p3 = p2 - p1; p3.Normalize();
		lightDirectionB[0] = p3.x; lightDirectionB[1] = p3.y; lightDirectionB[2] = p3.z;
	glLightfv(GL_LIGHT3, GL_SPOT_DIRECTION, lightDirectionB);
 
	glEnable(GL_COLOR_MATERIAL);
	glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE);
 
	// switch on lights
	glEnable(GL_LIGHT0);
	glEnable(GL_LIGHT1);
	glEnable(GL_LIGHT2);
	glEnable(GL_LIGHT3);
 
	return true; 
}

screenshots here
http://hw001.gate01.com/sean451/tmp/f1.jpg
http://hw001.gate01.com/sean451/tmp/b1.jpg

Thanks a lot

[chowe6685]

try positioning the light before positioning the camera

[Fahrenheit451]

Thanks. That seems to have fixed the spots appearing on the back of the sphere, but now my spots are all messed up. Not shining in the direction I calculate, but thats probably an issue with my direction calculations. I will work on it. Thanks again. btw. I realise I still have a bit more work to do on understanding the basics when it comes to viewing/transformations, but could you give me a brief explanation why placing the lights before the camera position worked better?

[plasmonster]

Fahrenheit451,

whenever you specify light positions, the gl assumes that you want to transform them with the model matrix. If you want your light position unaltered by he model matrix, simple load an identity matrix before setting them:

glMatrixMode( GL_MODELVIEW );
glPushMatrix();
glLoadIdentity();

// now set the lights...
//...

glPopMatrix();