OpenGL 光照方程的计算

       分析程序并计算，请看下面的一段程序，并计算三个顶点1、2和3处的光照的颜色值。必须写出过程，只有结果不得分。

#include <GL/glut.h>

void init(void) 
{
	GLfloat mat_ambient[] = { 0.2, 0.2, 0.2, 1.0 };
	GLfloat mat_diffuse[] = { 0.8, 0.8, 0.8, 1.0 };
	GLfloat mat_emission[] = { 0.0, 0.0, 0.0, 1.0 };
	GLfloat mat_specular[] = { 0.3, 0.3, 0.3, 1.0 };
	GLfloat mat_shininess[] = { 2.0 };

	GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };
	GLfloat light_ambient[] = {0.2, 0.2, 0.2, 1.0};
	GLfloat light_diffuse[] = {1.0, 1.0, 1.0, 1.0};
	GLfloat light_specular[] ={1.0, 1.0, 1.0, 1.0};
	GLfloat lmodel_ambient[] = {0.2, 0.2, 0.2, 1.0};
	glClearColor (0.0, 0.0, 0.0, 0.0);
	glShadeModel (GL_SMOOTH);
	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_EMISSION, mat_emission);
	glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);

	glLightfv(GL_LIGHT0, GL_POSITION, light_position);
	glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);
	glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);
	glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);

	glLightModelfv(GL_LIGHT_MODEL_AMBIENT, lmodel_ambient);
	glEnable(GL_LIGHTING);
	glEnable(GL_LIGHT0);
	glEnable(GL_DEPTH_TEST);
}
void display(void)
{
	glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glBegin(GL_TRIANGLES);
	glNormal3f(0.0f, 0.0f, 1.0f);
	glVertex3f(0.0, 0.0, 0.0);   //1
	glVertex3f(1.0, 0.0, 0.0);   //2
	glVertex3f(1.0, 1.0, 0.0);   //3
	glEnd();
	glFlush ();
}
void reshape (int w, int h)
{
	glViewport (0, 0, (GLsizei) w, (GLsizei) h);
	glMatrixMode (GL_PROJECTION);
	glLoadIdentity();
	if (w <= h)
		glOrtho (-1.5, 1.5, -1.5*(GLfloat)h/(GLfloat)w,1.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0);
	else
		glOrtho (-1.5*(GLfloat)w/(GLfloat)h,1.5*(GLfloat)w/(GLfloat)h, -1.5, 1.5, -10.0, 10.0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}
int main(int argc, char** argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
	glutInitWindowSize (500, 500); 
	glutInitWindowPosition (100, 100);
	glutCreateWindow (argv[0]);
	init ();
	glutDisplayFunc(display); 
	glutReshapeFunc(reshape);
	glutMainLoop();
	return 0;
}

        上述程序代码运行后，产生了一个三角形，使用QQ截图获取顶点1的像素值(该程序中顶点1的像素是(0,0,0))。。

       使用方法如下图：