C++ OpenGL lighting only lights certain walls

1
votes

I am lighting my scene in opengl and there are 4 walls, only 2 of them are being lit. I think it is something wrong with the normals but I am not sure.

This is the lighting code:

glShadeModel(GL_SMOOTH);
//glEnable(GL_CULL_FACE);

glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_LIGHT1);

GLfloat lightpos0[] = {-5, 1, 0, 0.};
GLfloat AmbientLight0[] = {0.2, 0.2, 0.2,1.0}; 
GLfloat DiffuseLight0[] = {0.8, 0.8, 0.8,1.0};
GLfloat SpecularLight0[] = {1.0, 1.0, 1.0,1.0};

glLightfv(GL_LIGHT0, GL_POSITION, lightpos0);
glLightfv(GL_LIGHT0, GL_AMBIENT, AmbientLight0);
glLightfv(GL_LIGHT0, GL_DIFFUSE, DiffuseLight0);
glLightfv(GL_LIGHT0, GL_SPECULAR, SpecularLight0);

GLfloat lightpos1[] = {5, 1, 0, 0};
GLfloat AmbientLight1[] = {0.2, 0.2, 0.2,1.0}; 
GLfloat DiffuseLight1[] = {0.8, 0.8, 0.8,1.0};
GLfloat SpecularLight1[] = {1.0, 1.0, 1.0,1.0};

glLightfv(GL_LIGHT1, GL_POSITION, lightpos1);
glLightfv(GL_LIGHT1, GL_AMBIENT, AmbientLight1);
glLightfv(GL_LIGHT1, GL_DIFFUSE, DiffuseLight1);
glLightfv(GL_LIGHT1, GL_SPECULAR, SpecularLight1);

This is the code for drawing the 4 walls.

    //north
    glBegin(GL_QUADS);
glNormal3f(1.0,0,0);
glVertex3f(-10,0,-10);
glVertex3f( 10,0,-10);
glVertex3f( 10,5,-10);
glVertex3f(-10,5,-10);
glEnd();
//south
glBegin(GL_QUADS);
glNormal3f(-1.0, 0, 0);
glVertex3f(-10,0, 10);
glVertex3f( 10,0, 10);
glVertex3f( 10,5, 10);
glVertex3f(-10,5, 10);
glEnd();
//east
glBegin(GL_QUADS);
glNormal3f(0,0, -1.0);
glVertex3f( 10,0,-10);
glVertex3f( 10,0,10);
glVertex3f( 10,5,10);
glVertex3f( 10,5,-10);
glEnd();
//west
glBegin(GL_QUADS);
glNormal3f(0,0,1.0);
glVertex3f( -10,0,-10);
glVertex3f( -10,0,10);
glVertex3f( -10,5,10);
glVertex3f( -10,5,-10);
glEnd();

If it helps, here's and image of whats happening: http://i.stack.imgur.com/xRgVL.png

2
c++opengllighting

2 Answers

2
votes

As pointed out by Vladislav Khorev, the normals must be directed out of the coordinate that is common to all points (given this special orthogonal arrangement). But also one should consider the winding of the polygons:

 // Polygon A --  north     Polygon B -- south
 glVertex3f(-10,0,-10);     glVertex3f(-10,0, 10); 
 glVertex3f( 10,0,-10);     glVertex3f( 10,0, 10);
 glVertex3f( 10,5,-10);     glVertex3f( 10,5, 10);
 glVertex3f(-10,5,-10);     glVertex3f(-10,5, 10);
 Normal(0,0,1),             Normal(0,0,-1);

The two polygons (north and south), are of different winding. The first is ClockWise observed from point 0,0,0 and the other of CCW. One should be consistent with these.

1
votes

It seems that you pass wrong normal vector to walls.

If your wall got Z = -10 for all points (wall is parallel to X), then it must have normal vector directed in positive direction of Z: (0,0,1). Same is true for all directions.

Try this:

glBegin(GL_QUADS);
glNormal3f(0,0,1);
glVertex3f(-10,0,-10);
glVertex3f( 10,0,-10);
glVertex3f( 10,5,-10);
glVertex3f(-10,5,-10);
glEnd();
//south
glBegin(GL_QUADS);
glNormal3f(0, 0, -1);
glVertex3f(-10,0, 10);
glVertex3f( 10,0, 10);
glVertex3f( 10,5, 10);
glVertex3f(-10,5, 10);
glEnd();
//east
glBegin(GL_QUADS);
glNormal3f(-1,0, -0);
glVertex3f( 10,0,-10);
glVertex3f( 10,0,10);
glVertex3f( 10,5,10);
glVertex3f( 10,5,-10);
glEnd();
//west
glBegin(GL_QUADS);
glNormal3f(1, 0, 0);
glVertex3f( -10,0,-10);
glVertex3f( -10,0,10);
glVertex3f( -10,5,10);
glVertex3f( -10,5,-10);
glEnd();