visualize-normals.cpp

void drawFaceNormals()
{
    glColor3f(0,0,1);  // The colour we will be drawing is white (red = 1, green = 1, blue = 1).
    vector<vec3> verts = trig.Vertices();
    vector<vec3> fnorms = trig.FaceNormals();

    vec3 fnorm, pos, from, to;

    glBegin(GL_LINES);
    for(int i = 0; i < fnorms.size(); i++){
        fnorm = 10.0f*fnorms[i];
        vec3 pos1 = verts[i*3];
        vec3 pos2 = verts[i*3+1];
        vec3 pos3 = verts[i*3+2];

        float mul = 1/2.0f;
        vec3 center = mul*pos1 + mul*(pos2-pos1) + mul*(pos3 - mul*(pos2-pos1));

        from = vec3(mvp * vec4(center, 1.0f));
        to = vec3(mvp * vec4(center+fnorm, 1.0f));

        glVertex3f(from.x, from.y, from.z);
        glVertex3f(to.x, to.y, to.z); 
    }
    glEnd();
}

void drawVertexNormals()
{
    vector<vec3> verts = trig.Vertices();
    vector<vec3> vnorms = trig.VertexNormals();

    vec3 vnorm, pos, from, to;

    glColor3f(0,1,0);  // The colour we will be drawing is white (red = 1, green = 1, blue = 1).
    glBegin(GL_LINES);
    for(int i = 0; i < vnorms.size(); i++){
        vnorm = 10.0f*vnorms[i];
        vec3 pos = verts[i];

        from = vec3(mvp * vec4(pos, 1.0f));
        to = vec3(mvp* vec4(pos+vnorm, 1.0f));

        glVertex3f(from.x, from.y, from.z);
        glVertex3f(to.x, to.y, to.z); 
    }
    glEnd();
}