Lighting and material color problems - opengl

Question

I can't change any object color when lighting is enabled.
This is my init function (the part of the light and material):
glEnable (GL_LIGHTING);
glEnable (GL_LIGHT0);
GLfloat light_ambient[] = {0.5, 0.5, 0.5, 1.0};
GLfloat light_diffuse[] = {0.0, 0.5, 0.5, 1.0};
GLfloat light_specular[] = {0.0, 0.0, 0.5, 1.0};
GLfloat light_position[]={0, -1.0, 0, 0.0};
glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);
glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);
glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);
glLightfv(GL_LIGHT0, GL_POSITION, light_position);
Each object has a vector of colors. This is how I draw my objects:
float mat_a[] = {0.0, 0.0, 0.0, 1.0};
float mat_d[] = {0.0, 0.0, 0.0, 1.0};
float mat_s[] = {0.0, 0.0, 0.0, 1.0};
...
colors_vect = some_object->getColor();
glDisable(GL_COLOR_MATERIAL);
mat_a[0] = colors_vect.at(0);
mat_a[1] = colors_vect.at(1);
mat_a[2] = colors_vect.at(2);
mat_d[0] = colors_vect.at(3); //The values are correct.
mat_d[1] = colors_vect.at(4);
mat_d[2] = colors_vect.at(5);
mat_s[0] = colors_vect.at(6);
mat_s[1] = colors_vect.at(7);
mat_s[2] = colors_vect.at(8);
glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, mat_a);
glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, mat_d);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, mat_s);
glEnable(GL_COLOR_MATERIAL);
glBegin(GL_POLYGON);
...
This code doesn't work. I tried to give the mat some random values and still nothing changes.
What am I doing wrong? Any help would be appreciated!

Answer 1

Your problem is caused by this line:
glEnable(GL_COLOR_MATERIAL);
This enables functionality that allows material properties to track the current color, which is the color set with regular glColor() calls. If this is enabled, glColorMaterial() controls which parts of the material parameters track the current color. The default is GL_AMBIENT_AND_DIFFUSE, which means that the current color is used for the ambient and diffuse material parameters.
You need to make a choice about how you want to update your material properties:
If you need to change colors very frequently, it can be most efficient to enable GL_COLOR_MATERIAL, and use glColor() to update the material properties.
You can use glColorMaterialfv(), which gives you more control, and e.g. allows you to set different colors for ambient and diffuse. For this approach, you need to keep GL_COLOR_MATERIAL disabled.
You used a mix of these two, where you set the material properties with glColorMaterialfv(), but then also enabled GL_COLOR_MATERIAL. This means that the ambient and diffuse material properties you set are not used. Instead the current color is used for those two properties. These properties would then change any time you call glColor(). If you never call glColor(), they would use the default value for the current color, which is white (1.0, 1.0, 1.0, 1.0).