glEnable(GL_COLOR_MATERIAL) applying to all drawn objects

问题

I'm developing a version of the Frogger game for a University project, and we got to the light and materials part. The problem I have is: when I set the materials for the frog, it applies them to all other objects that are drawn. How do I make it so that it only applies to the frog? If I disable GL_COLOR_MATERIAL after the draw or after the material properties have been set, everything becomes red.

void Frog::draw(void)
{
    Vector3 _pos = Entity::getPosition();

    glPushMatrix();

    glEnable(GL_COLOR_MATERIAL);

    GLfloat greenEmissiveMaterial[] = {1.0, 0.0, 0.0};
    glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE);

    GLfloat mat_ambient[] = {0.7, 0.0, 0.0, 1.0};
    GLfloat mat_diffuse[] = { 0.7, 0.0, 0.0, 1.0 };
    GLfloat mat_specular[] = { 0.0, 0.0, 0.0, 0.0 };
    GLfloat mat_shininess[] = {1.8 };

    glColor3f(1.0, 0.0, 0.0);

    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);

glDisable(GL_COLOR_MATERIAL);

    glScalef(0.1, 0.1, 0.1);
    glTranslatef( _pos.getX()*U , _pos.getY()*U , 1 );
    //CORPO
    glPushMatrix();
    glColor3f(0.0, 1.0, 0.0);
    glutSolidSphere(0.5,50,50);
    glPopMatrix();

    glPushMatrix();
    glColor3f(0.0, 1.0, 0.0);
    glTranslatef(0.0, 0.5, 0.0);
    glutSolidSphere(0.3,50,50);
    glPopMatrix();


    glPopMatrix();

}

回答1:

Enabling the state GL_COLOR_MATERIAL causes the material color to track the current color for the face you specify in a call to glColorMaterial (...). In other words, while GL_COLOR_MATERIAL is enabled and glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE) has been set, the value of GL_AMBIENT and GL_DIFFUSE are determined exclusively by the current color for the front-face.

Thus, the the following call:

glColor3f (1.0f, 0.0f, 0.0f);

Is effectively equivalent to this in your software:

glColor3f (1.0f, 0.0f, 0.0f); // Set the "current" color

GLfloat red [3] = { 1.0f, 0.0f, 0.0f };

glMaterialfv (GL_FRONT, GL_AMBIENT_AND_DIFFUSE, red);

You can see that you have changed the value of GL_AMBIENT and GL_DIFFUSE to red. And you also tried to change the ambient / diffuse material color manually while that state was enabled in your original code, which is not going to do anything.

The behavior above is described in more detail here:

Name

glColorMaterial — cause a material color to track the current color

C Specification

void glColorMaterial( GLenum face, GLenum mode);

Description

glColorMaterial specifies which material parameters track the current color. When GL_COLOR_MATERIAL is enabled, the material parameter or parameters specified by mode, of the material or materials specified by face, track the current color at all times.

To enable and disable GL_COLOR_MATERIAL, call glEnable and glDisable with argument GL_COLOR_MATERIAL. GL_COLOR_MATERIAL is initially disabled.

If you want to stop tracking the current color and use the values in mat_ambient and mat_diffuse, then you should add the following code sometime after you disable GL_COLOR_MATERIAL:

glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);

来源：https://stackoverflow.com/questions/26638039/glenablegl-color-material-applying-to-all-drawn-objects

标签

opengl

visual-c++