OpenGL--光照

• 理论基础
  1，人眼所看到的五颜六色的世界是由于物体表面反射到眼睛的颜色形成的，而这个反射颜色是由物体本身和光源共同决定的。某种颜色的物体反射对应颜色的光，吸收其它颜色的光，如红色物体吸收全部的G,B颜色，反射全部的R颜色。opengl把光单独分成4种类型：环境光(均匀充满场景)，散射光(手电筒)，镜面光(朝特定一方向反射)，发射光(夜明珠)。他们单独计算，最后叠加在一起，构成整个光照系统。
  2，法线向量：是一条垂直于某个表面的方向向量。除了顶点外，不能为多边形其他地方分配法线。同一个多边形的顶点可能共享同一条法线(平表面)，也可能具有不同的法线(曲面)。物体的法线向量其实就是定义了它的表面在空间中的方向。具体地说，定义了它相对光源的方向，opengl就是使用法线向量确定这个物体的各个顶点所接收的光照。(glNormal)
  3，光照操作一般就是指定3个东西：一，光照模型 二，光源属性 三，材料属性。如果没有指定，开启光源也会给予这3个东西默认值。

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• 实例代码
  1，绘制光照球体

#include "GLTools.h"
#include "GLShaderManager.h"

#ifdef __APPLE__
#include 
#else
#define FREEGLUT_STATIC
#include 
#endif

void init(void)
{
    GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat mat_shininess[] = { 50.0 };

    GLfloat light_ambient[] = {0.0, 0.0, 1.0, 1.0};
    GLfloat light_diffuse[] = {1.0, 0.0, 0.0, 1.0};
    GLfloat light_specular[] = {1.0, 1.0, 1.0, 1.0};
    /*方向性光源(最后参数为0)：光源位于无限远处，当光线到达物体表面时，可以认为所有光线都是平行的。如太阳光
     位置性光源(最后参数非零)：不同角度位置光照强度不同，表现更加逼真。如聚光灯*/
    GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };

    glClearColor (0.0, 0.0, 0.0, 0.0);
    glShadeModel (GL_SMOOTH);

    /*设置材料与光源属性*/
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);
    //光源位置
    glLightfv(GL_LIGHT0, GL_POSITION, light_position);
    //环境光
    glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);
    //散射光
    glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);
    //镜面强度
    glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);

    //激活光照并启动0号光源(启动了就会有默认属性)
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);
}

void display(void)
{
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glutSolidSphere (1.0, 20, 16);//绘制球体(它同时也定义了它的法线向量)
    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();
}

void keyboard(unsigned char key, int x, int y)
{
    switch (key) {
        case 27:
            exit(0);
            break;
    }
}

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);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;
}

2，光源的移动

#include "GLTools.h"
#include "GLShaderManager.h"

#ifdef __APPLE__
#include 
#else
#define FREEGLUT_STATIC
#include 
#endif

static int spin = 0;

void init(void)
{
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glShadeModel (GL_SMOOTH);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);
}

void display(void)
{
    GLfloat position[] = { 0.0, 0.0, 1.5, 1.0 };

    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glPushMatrix ();
        gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

        glPushMatrix ();
            /*光源旋转*/
            glRotated ((GLdouble) spin, 1.0, 0.0, 0.0);
            glLightfv (GL_LIGHT0, GL_POSITION, position);

            /*绘制一个不受光照的正方体表示光源*/
            glTranslated (0.0, 0.0, 1.5);
            glDisable (GL_LIGHTING);
            glColor3f (0.0, 1.0, 1.0);
            glutWireCube (0.1);
            glEnable (GL_LIGHTING);
        glPopMatrix ();

        glutSolidTorus (0.275, 0.85, 8, 15);
    glPopMatrix ();

    glFlush ();
}

void reshape (int w, int h)
{
    glViewport (0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(40.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void mouse(int button, int state, int x, int y)
{
    switch (button)
    {
        case GLUT_LEFT_BUTTON:
            if (state == GLUT_DOWN)
            {
                spin = (spin + 30) % 360;
                glutPostRedisplay();
            }
            break;
        default:
            break;
    }
}

void keyboard(unsigned char key, int x, int y)
{
    switch (key)
    {
        case 27:
            exit(0);
            break;
    }
}

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);
    glutMouseFunc(mouse);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;
}

3，材料属性变化对表现的影响

#include "GLTools.h"
#include "GLShaderManager.h"

#ifdef __APPLE__
#include 
#else
#define FREEGLUT_STATIC
#include 
#endif

void init(void)
{
    GLfloat ambient[] = { 0.0, 0.0, 0.0, 1.0 };
    GLfloat diffuse[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat position[] = { 0.0, 3.0, 2.0, 0.0 };
    GLfloat lmodel_ambient[] = { 0.4, 0.4, 0.4, 1.0 };

    glClearColor(0.0, 0.1, 0.1, 0.0);
    glEnable(GL_DEPTH_TEST);
    glShadeModel(GL_SMOOTH);
    //光源属性
    glLightfv(GL_LIGHT0, GL_AMBIENT, ambient);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse);
    glLightfv(GL_LIGHT0, GL_POSITION, position);
    //光照模型
    glLightModelfv(GL_LIGHT_MODEL_AMBIENT, lmodel_ambient);//环境光强度
    glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER, GL_FALSE);//局部观察点还是无限远观察点

    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
}


void display(void)
{
    GLfloat no_mat[] = { 0.0, 0.0, 0.0, 1.0 };
    GLfloat mat_ambient[] = { 0.7, 0.7, 0.7, 1.0 };
    GLfloat mat_ambient_color[] = { 0.8, 0.8, 0.2, 1.0 };
    GLfloat mat_diffuse[] = { 0.1, 0.5, 0.8, 1.0 };
    GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat no_shininess[] = { 0.0 };
    GLfloat low_shininess[] = { 5.0 };
    GLfloat high_shininess[] = { 100.0 };
    GLfloat mat_emission[] = {0.3, 0.2, 0.2, 0.0};

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    /*材料属性*/
    glPushMatrix();
    glTranslatef (-3.75, 3.0, 0.0);
    //材料的环境颜色
    glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);
    //材料的散射颜色
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    //材料的镜面颜色
    glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
    //镜面指数
    glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
    //材料的发射颜色
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（1，2）*/
    glPushMatrix();
    glTranslatef (-1.25, 3.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（1，3）*/
    glPushMatrix();
    glTranslatef (1.25, 3.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（1，4）*/
    glPushMatrix();
    glTranslatef (3.75, 3.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
    glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（2，1）*/
    glPushMatrix();
    glTranslatef (-3.75, 0.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
    glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（2，2）*/
    glPushMatrix();
    glTranslatef (-1.25, 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, low_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（2，3）*/
    glPushMatrix();
    glTranslatef (1.25, 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, high_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（2，4）*/
    glPushMatrix();
    glTranslatef (3.75, 0.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
    glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（3，1）*/
    glPushMatrix();
    glTranslatef (-3.75, -3.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
    glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（3，2）*/
    glPushMatrix();
    glTranslatef (-1.25, -3.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（3，3）*/
    glPushMatrix();
    glTranslatef (1.25, -3.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    /*（3，4）*/
    glPushMatrix();
    glTranslatef (3.75, -3.0, 0.0);
    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);
    glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);
    glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);
    glutSolidSphere(1.0, 16, 16);
    glPopMatrix();

    glFlush();
}

void reshape(int w, int h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= (h * 2))
        glOrtho (-6.0, 6.0, -3.0*((GLfloat)h*2)/(GLfloat)w,
                 3.0*((GLfloat)h*2)/(GLfloat)w, -10.0, 10.0);
    else
        glOrtho (-6.0*(GLfloat)w/((GLfloat)h*2),
                 6.0*(GLfloat)w/((GLfloat)h*2), -3.0, 3.0, -10.0, 10.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
    switch (key) {
        case 27:
            exit(0);
            break;
    }
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize (600, 450);
    glutCreateWindow(argv[0]);
    init();
    glutReshapeFunc(reshape);
    glutDisplayFunc(display);
    glutKeyboardFunc (keyboard);
    glutMainLoop();
    return 0;
}

4，颜色材料模式：频繁更改材料属性效率更高的方式

#include "GLTools.h"
#include "GLShaderManager.h"

#ifdef __APPLE__
#include 
#else
#define FREEGLUT_STATIC
#include 
#endif
//需要频繁改变的材料属性
GLfloat diffuseMaterial[4] = { 0.5, 0.5, 0.5, 1.0 };

void init(void)
{
    GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };

    glClearColor (0.0, 0.0, 0.0, 0.0);
    glShadeModel (GL_SMOOTH);
    glEnable(GL_DEPTH_TEST);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial);
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialf(GL_FRONT, GL_SHININESS, 25.0);
    glLightfv(GL_LIGHT0, GL_POSITION, light_position);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);

    /*频繁更改材料属性，这个效率更高，它只需要更改相应颜色值
     就可以更改材料属性，减少glMaterial*()调用次数*/
    glColorMaterial(GL_FRONT, GL_DIFFUSE);

     //激活颜色材料模式
    glEnable(GL_COLOR_MATERIAL);
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glutSolidSphere(1.0, 20, 16);
    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();
}

void mouse(int button, int state, int x, int y)
{
    //更改材料散射颜色
    switch (button) {
        case GLUT_LEFT_BUTTON:
            if (state == GLUT_DOWN) {
                diffuseMaterial[0] += 0.1;
                if (diffuseMaterial[0] > 1.0)
                    diffuseMaterial[0] = 0.0;
                glColor4fv(diffuseMaterial);
                glutPostRedisplay();
            }
            break;
        case GLUT_MIDDLE_BUTTON:
            if (state == GLUT_DOWN) {
                diffuseMaterial[1] += 0.1;
                if (diffuseMaterial[1] > 1.0)
                    diffuseMaterial[1] = 0.0;
                glColor4fv(diffuseMaterial);
                glutPostRedisplay();
            }
            break;
        case GLUT_RIGHT_BUTTON:
            if (state == GLUT_DOWN) {
                diffuseMaterial[2] += 0.1;
                if (diffuseMaterial[2] > 1.0)
                    diffuseMaterial[2] = 0.0;
                glColor4fv(diffuseMaterial);
                glutPostRedisplay();
            }
            break;
        default:
            break;
    }
}

void keyboard(unsigned char key, int x, int y)
{
    switch (key) {
        case 27:
            exit(0);
            break;
    }
}

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);
    glutMouseFunc(mouse);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;

}