Inconsistency of shading in polygons on the same axis in OpenGL - opengl

Question

I am building a house in OpenGL. On the outside and on the inside where there are doors or windows, I use a Quad to go below and above the windows all the way around the house, and then a quad to fill in the gaps between windows. These will have the same plane value, but for some reason GL_LIGHT passes shadows onto some. Any clue why?
Quad between windows
glBegin(GL_QUADS);
glTexCoord2d(0, 0);glVertex3d(0, 1.1, 0);
glTexCoord2d(2, 0);glVertex3d(0, 1.1, 2);
glTexCoord2d(2, 1.6);glVertex3d(0, 2.7, 2);
glTexCoord2d(0, 1.6);glVertex3d(0, 2.7, 0);
glEnd();
Below windows
glBegin(GL_QUADS);
glTexCoord2d(0, 0);glVertex3d(0, 0.1, 0);
glTexCoord2d(15, 0);glVertex3d(0, 0.1, 15);
glTexCoord2d(15, 1);glVertex3d(0, 1.1, 15);
glTexCoord2d(0.0, 1);glVertex3d(0, 1.1, 0);
glEnd();
Above windows
glBegin(GL_QUADS);
glTexCoord2d(0, 2.6);glVertex3d(0, 2.7, 0);
glTexCoord2d(15, 2.6);glVertex3d(0, 2.7, 15);
glTexCoord2d(15, 3.0);glVertex3d(0, 3.1, 15);
glTexCoord2d(0.0,3.0);glVertex3d(0, 3.1, 0);
glEnd();
here is the code for the light
GLfloat light_position[] = { 50, 50, -1.0};
GLfloat diffuse[] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat specular[] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat ambient[] = { 1.0, 1.0, 1.0, 1.0 };
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_LIGHT1);
glEnable(GL_NORMALIZE);
glLightfv(GL_LIGHT0, GL_POSITION , light_position );
glLightfv(GL_LIGHT0, GL_SPECULAR , specular);
glLightfv(GL_LIGHT0, GL_DIFFUSE , diffuse );
glLightfv(GL_LIGHT0, GL_AMBIENT , ambient );
Here is a screenshot of the result
http://imgur.com/WsgZWBF
Why is it doing this, and is there any way to fix it?

Answer 1

You need to supply (meaningful) vertex/face normals for OpenGL's lighting to work properly:
18.020 Why are my objects all one flat color and not shaded and illuminated?
This effect occurs when you fail to supply a normal at each vertex.
OpenGL needs normals to calculate lighting equations, and it won't calculate normals for you (with the exception of evaluators). If your application doesn't call glNormal*(), then it uses the default normal of (0.0, 0.0, 1.0) at every vertex. OpenGL will then compute the same, or nearly the same, lighting result at each vertex. This will cause your model to look flat and lack shading.
The solution is to simply calculate the normals that need to be specified at any given vertex. Then send them to OpenGL with a call to glNormal3f() just prior to specifying the vertex, which the normal is associated with.