Illumination changes when rotating camera

OpenGL OpenGL: Basic Coding
1

Hello, I have a problem with lighting in OpenGL, when I rotate camera changes the illumination of the scene.
The light is directional: incident at the same angle for all objects, like the sun.

		const GLfloat			lightAmbient[] = {0.2, 0.2, 0.2, 1.0};
		const GLfloat			lightDiffuse[] = {1.0, 0.6, 0.0, 1.0};
		const GLfloat			matAmbient[] = {0.6, 0.6, 0.6, 1.0};
		const GLfloat			matDiffuse[] = {1.0, 1.0, 1.0, 1.0};	
		const GLfloat			matSpecular[] = {1.0, 1.0, 1.0, 1.0};
		const GLfloat			lightPosition[] = {0.0, 0.0, 1.0, 0.0}; 
		const GLfloat			lightShininess = 100.0;

		glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, matAmbient);
		glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, matDiffuse);
		glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, matSpecular);
		glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, lightShininess);
		glLightfv(GL_LIGHT0, GL_AMBIENT, lightAmbient);
		glLightfv(GL_LIGHT0, GL_DIFFUSE, lightDiffuse);
		glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);

I tried calling glLightfv on each frame after tell opengl which is the matrix of the camera, but still happening:

glMatrixMode(GL_MODELVIEW);




float mat[4*4]={ CamMatrix->iM[0], CamMatrix->iM[4], -CamMatrix->iM[ 8], 0,
			 CamMatrix->iM[1], CamMatrix->iM[5], -CamMatrix->iM[ 9], 0,
			 CamMatrix->iM[2], CamMatrix->iM[6], -CamMatrix->iM[10], 0,
                         CamMatrix->iM[3], CamMatrix->iM[7], -CamMatrix->iM[11], 1  };


glLoadMatrixf( mat );
glPushMatrix();

float lightPosition[] = {0.0f, 2.0f, 1.0f, 0.0f}; 
glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);

Thanks in advance.

2

This should work, you need to ensure that the matrix has the viewing transform and only the viewing transform on the matrix stack.

If you load another viewing matrix differently then you’ll get a discrepancy.

You’re dicking around with that matrix, it needs to be the SAME matrix as the one loaded for viewing and loaded in the same way as viewing.

3

But in my engine, I set modelview matrix for each 3D object:

//—Generate rotate matrix for OpenGl.
//—Final matrix is CamMatrix ObjectMatrix
float mat[44]={ FinalMatrix->iM[0], FinalMatrix->iM[4], -FinalMatrix->iM[ 8], 0,
FinalMatrix->iM[1], FinalMatrix->iM[5], -FinalMatrix->iM[ 9], 0,
FinalMatrix->iM[2], FinalMatrix->iM[6], -FinalMatrix->iM[10], 0,
FinalMatrix->iM[3], FinalMatrix->iM[7], -FinalMatrix->iM[11], 1 };

glLoadMatrixf( mat );

.
.
.

glDrawElements( GL_TRIANGLES, iGlTriCount, GL_UNSIGNED_SHORT, iGlTris );

Where should I put glLightfv(GL_LIGHT0, GL_POSITION, lightPosition); ?

I do not tell opengl which is the camera matrix, I only use camera matrix to generate FinalMatrix. I do not use glLookAt, it is not available in iphone.

Thank you very much for your help

4

Where should I put glLightfv(GL_LIGHT0, GL_POSITION, lightPosition); ?

Right after the camera transform, before drawing any object

5

Yes, I am doing it there.

6

and you pop the matrix after the camera transform?