3 MB WMV movie showing the issue: http://vault101.co.uk/downloads/fog_glitch.wmv
It’s late/early (however you view it) and my brain is fried.
When rotating the camera left/right and even up/down any object that is lit using OpenGL lighting fades to black the further we get from an imaginary sweet spot.
I’m sure I’ve hit this issue before and can’t remember how I solved it, or what was causing it.
A quick search on this forum and another opengl one turned up nothing obvious but I’m half asleep 
sample of the code - removed a load of setup junk included loading textures - hopefully this is useful in solving this, I’ve pseudo coded a heap of the tree/terrain junk as it’s very lengthy and spread across heaps of class files.
I just have my fingers crossed that I can find how I solved this last time (searches subversion repository logs) or someone can go “Ah yeah it’s cos of this…”
pre() { // before 'running'
ortho_mode();
gl.glClearColor(fog_colour[0], fog_colour[1], fog_colour[2], fog_colour[3]);
// set the fog attributes
gl.glFogf(gl.GL_FOG_START, near_distance);
gl.glFogf(gl.GL_FOG_END, far_distance);
gl.glFogfv(gl.GL_FOG_COLOR, fog_colour, 0);
gl.glFogi(gl.GL_FOG_MODE, gl.GL_EXP);
gl.glFogf(gl.GL_FOG_DENSITY, fog_density);
// enable the fog
gl.glEnable(gl.GL_FOG);
// enable the default light
gl.glEnable(gl.GL_LIGHTING);
gl.glEnable(gl.GL_LIGHT0);
if (!gl.glIsEnabled(gl.GL_DEPTH_TEST)) {
gl.glEnable(gl.GL_DEPTH_TEST);
}
}
main_loop() {
draw_perspective();
draw_ortho();
}
draw_perspective() {
if (!perspective_mode)
perspective_mode();
gl.glLoadIdentity();
gl.glPolygonMode(gl.GL_FRONT_AND_BACK, gl.GL_FILL);
glu.gluLookAt(MEngine.g_Camera.m_vPosition.x,
MEngine.g_Camera.m_vPosition.y,
MEngine.g_Camera.m_vPosition.z,
MEngine.g_Camera.m_vView.x,
MEngine.g_Camera.m_vView.y,
MEngine.g_Camera.m_vView.z,
MEngine.g_Camera.m_vUpVector.x,
MEngine.g_Camera.m_vUpVector.y,
MEngine.g_Camera.m_vUpVector.z);
pseudo -> turn off depth testing
pseudo -> draw sky box
pseudo -> turn on depth testing
pseudo -> turn on face culling (front)
pseudo -> draw terrain using display lists
pseudo -> cull face (back)
pseudo -> draw billboards
pseudo -> draw trees using display lists
pseudo -> turn off depth testing
pseudo -> turn off face culling
}
draw_ortho() {
if (!ortho_mode)
ortho_mode();
// nothing here yet but a call to ortho_mode ensures we're still pushing those matricies to avoid GL_STACK_UNDERFLOW
}
perspective_mode() {
gl.glMatrixMode(gl.GL_PROJECTION);
gl.glPopMatrix();
gl.glMatrixMode(gl.GL_MODELVIEW);
gl.glPopMatrix();
if (!gl.glIsEnabled(gl.GL_CULL_FACE))
gl.glEnable(gl.GL_CULL_FACE);
if (!gl.glIsEnabled(gl.GL_DEPTH_TEST))
gl.glEnable(gl.GL_DEPTH_TEST);
}
ortho_mode() {
if (gl.glIsEnabled(gl.GL_CULL_FACE))
gl.glDisable(gl.GL_CULL_FACE); // Disable Face Culling, as this won't show blended
if (gl.glIsEnabled(gl.GL_DEPTH_TEST))
gl.glDisable(gl.GL_DEPTH_TEST);
gl.glMatrixMode(gl.GL_PROJECTION);
gl.glPushMatrix();
gl.glLoadIdentity();
gl.glOrtho(0, SL.getInt(SL.I_SCREENWIDTH), SL.getInt(SL.I_SCREENHEIGHT), 0, 0, 1);
gl.glMatrixMode(gl.GL_MODELVIEW);
gl.glPushMatrix();
gl.glLoadIdentity();
}