two sided lighting invalid

[nkrobot]

Here is the problem. I use the methods
glLightModeli(GL_LIGHT_MODEL_TWO_SIDE,GL_TRUE); to make the polygon show both of the two sides. But actually if I add
a negtive matrixtransform when drawing a polygon ,both of the two sides will be unlit(dark actually)
. the question is I must use the two sided lighting and I have to use this type of matrix . Also the vetex's order I use is uncertain.
So Is there any way to solve the problem?
Thank you!
The code here...

 //The matrix which may cause problem
GLfloat a[16] = {
	1,0,0,0,
	0,-1,0,0,//If a negtive matrix, an error accur.
	0,0,1,0,
	0,0,0,1
};//I know use the negtive num may cause the problem, but I have to use this because a lot of data I have contain this kind of matrix.
 
int InitGL(GLvoid)
{	
	//......
	//enable light
	glEnable(GL_LIGHTING);
	glEnable(GL_LIGHT0);
	glFrontFace(GL_CCW);//it dosen't matter whether use GL_CW or GL_CCW
	glLightModeli(GL_LIGHT_MODEL_TWO_SIDE,GL_TRUE);//if set two face show, sometimes the result is not as I expect.
	//.....							
}
//Draw scene
int DrawGLScene(GLvoid)					
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	
	glLoadIdentity();
	glMultMatrixf(a);//using the matrix causing problem
 
	glTranslatef(-1.5f,0.0f,-12.0f);					
	glRotatef(rtri,0.0f,1.0f,0.0f);						
	//just draw a single triangle. but the light can effect neither of the two faces when I use the matrix which contains negtive num.
	glBegin(GL_TRIANGLES);								
		glVertex3f( 0.0f, 1.0f, 0.0f);					
		glVertex3f(-1.0f,-1.0f, 0.0f);					
		glVertex3f( 1.0f,-1.0f, 0.0f);					
	glEnd();											
	return TRUE;									
}

[Dark Photon]

..if I add a negtive matrixtransform when drawing a polygon ,both of the two sides will be unlit...So Is there any way to solve the problem?

...
glBegin(GL_TRIANGLES);								
glVertex3f( 0.0f, 1.0f, 0.0f);					
glVertex3f(-1.0f,-1.0f, 0.0f);					
glVertex3f( 1.0f,-1.0f, 0.0f);					
glEnd();
...

Where are your vertex normals? You need normals for OpenGL to evaluate the lighting at each vertex for you. See glNormal3f

I never use two-sided lighting but my guess is you'll need to disable back-face culling: glDisable( GL_CULL_FACE ). Tweaking that alone may be enough. That y inversion in your MODELVIEW matrix is switching the winding order (i.e. whether your poly is front or back facing).