Specular lighting not working [duplicate] - c++

Question

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No spot of light on cube
(1 answer)
Closed 5 years ago.
I created a 3D scene where I added a light source and a 3D box, which should be illuminated by the light source. Both Ambient and Diffuse colors seem to work properly, but the specular color does not seem to be calculated correctly. When moving the camera in front of the side with the light source, no specular 'dot' can be seen. But when i move the camera towards the top of the cube and look at the origin (0, 0, 0), a faint specular 'dot' can be seen on the illuminated side of the cube.
My question is the following: what am I doing wrong?
Everything in the code below happens in the modelMatrix, and the _nav member manages the camera movement.
Here's the code:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(_nav->getCamPosx(), _nav->getCamPosy(), _nav->getCamPosz(),
_nav->getCamViewx(), _nav->getCamViewy(), _nav->getCamViewz(),
_nav->getCamUpx(), _nav->getCamUpy(), _nav->getCamUpz());
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
GLfloat qaAmbientLight[] = {0.2f, 0.2f, 0.2f, 1.0f};
GLfloat qaDiffuseLight[] = {0.8f, 0.8f, 0.8f, 1.0f};
GLfloat qaSpecularLight[] = {1.0f, 0.0f, 0.0f, 1.0f}; //red for testing
glLightfv(GL_LIGHT0, GL_AMBIENT, qaAmbientLight);
glLightfv(GL_LIGHT0, GL_DIFFUSE, qaDiffuseLight);
glLightfv(GL_LIGHT0, GL_SPECULAR, qaSpecularLight);
// Set the light position
GLfloat qaLightPosition[] = {0.5f, 0.5f, 1.2f, 1.0f};
glLightfv(GL_LIGHT0, GL_POSITION, qaLightPosition);
GLfloat cyan[] = {0.f, .8f, .8f, 1.f};
GLfloat white[] = {0.8f, 0.8f, 0.8f, 1.0f};
//GLfloat dark[] = {0.0, 0.0, 0.0, 1.0};
glMaterialfv(GL_FRONT, GL_AMBIENT, cyan);
glMaterialfv(GL_FRONT, GL_DIFFUSE, cyan);
glMaterialfv(GL_FRONT, GL_SPECULAR, white);
GLfloat shininess[] = {80};
glMaterialfv(GL_FRONT, GL_SHININESS, shininess);
glBegin(GL_QUADS);
glNormal3f(0.0f, -1.0f, 0.0f);
glVertex3f(0.1f, 0.0f, 0.1f);
glVertex3f(1.0f, 0.0f, 0.1f);
glVertex3f(1.0f, 0.0f, 1.0f);
glVertex3f(0.1f, 0.0f, 1.0f);
glNormal3f(0.0f, 0.0f, -1.0f);
glVertex3f(0.1f, 0.0f, 0.1f);
glVertex3f(1.0f, 0.0f, 0.1f);
glVertex3f(1.0f, 1.0f, 0.1f);
glVertex3f(0.1f, 1.0f, 0.1f);
glNormal3f(-1.0f, 0.0f, 0.0f);
glVertex3f(0.1f, 0.0f, 0.1f);
glVertex3f(0.1f, 0.0f, 1.0f);
glVertex3f(0.1f, 1.0f, 1.0f);
glVertex3f(0.1f, 1.0f, 0.1f);
//face that gets illuminated
glNormal3f(0.0f, 0.0f, 1.0f);
glVertex3f(1.0f, 0.0f, 1.0f);
glVertex3f(0.1f, 0.0f, 1.0f);
glVertex3f(0.1f, 1.0f, 1.0f);
glVertex3f(1.0f, 1.0f, 1.0f);
glNormal3f(1.0f, 0.0f, 0.0f);
glVertex3f(1.0f, 0.0f, 0.1f);
glVertex3f(1.0f, 0.0f, 1.0f);
glVertex3f(1.0f, 1.0f, 1.0f);
glVertex3f(1.0f, 1.0f, 0.1f);
glNormal3f(0.0f, 1.0f, 0.0f);
glVertex3f(0.1f, 1.0f, 0.1f);
glVertex3f(1.0f, 1.0f, 0.1f);
glVertex3f(1.0f, 1.0f, 1.0f);
glVertex3f(0.1f, 1.0f, 1.0f);
glEnd();
Facing cube side with light source:
Top view of the cube, the faint red is the specular 'dot':

Answer 1

In fixed function OpenGL illumination is calculated only at the vertices and the resulting colour then interpolated across the faces. For specular reflexes to show up then you need sufficiently many vertices so that there's actually enough spatial sampling.
Obviously it's not very efficient to subdivide meshes, just to provide enough sampling points for illumination purposes. So over the years a number of per-pixel-illumination techniques were developed. It's pretty straightforward to implement using shaders ( https://www.opengl.org/sdk/docs/tutorials/ClockworkCoders/lighting.php ).