第五章_OpenGL光照与材质(二)

第五章光照与材质

5.8 全局环境光

每个光源可以有自己的环境光，但也可以有不来自于任何光源的环境光，指定环境光的方法是：

利用参数GL_LIGHT_MODEL_AMBIENT来调用函数glLightModel*()。

如：

float model_ambient[] = { 0.2 , 0.2 , 0.2 , 1.0 };

glLightModelfv(GL_LIGHT_MODEL_AMBIENT , model_ambient ) ;

上述代码为场景中的物体提供了软弱的白色环境光，所以即使场景中没有任何光源，也可以看到场景中的物体。

【综合示例EP5-5】场景中绘制一组静物模型，然后加入一个简单的光照，先使用光源自己的环境光，再统一使用全局环境光。

代码如下：

#include "stdafx.h"

int nAngleY=0; // 沿Y轴旋转的角度

int nAngleX=0; // 沿X轴旋转的角度

int nAngleZ=0; // 沿Z轴旋转的角度

void CALLBACK ClockwiseRotateByX()

{

nAngleX--;

}

void CALLBACK CounterClockwiseRotateByX()

{

nAngleX++;

}

void CALLBACK ClockwiseRotateByZ()

{

nAngleZ--;

}

void CALLBACK CounterClockwiseRotateByZ()

{

nAngleZ++;

}

void CALLBACK ClockwiseRotateByY()

nAngleY--;

}

void CALLBACK CounterClockwiseRotateByY()

{

nAngleY++;

}

void myinit (void)

{

/* 将背景清为白色*/

glClearColor (0.0, 0.0,0.0, 1.0);

glShadeModel (GL_SMOOTH);

GLfloat ambient[] = { 0.5, 0.0, 0.0, 1.0 };

GLfloat specular[] = { 1.0, 1.0, 0.0, 1.0 };

GLfloat diffuse[] = { 0.5, 0.5, 0.5, 1.0 };

GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };

GLfloat model_ambient[] = { 0.3, 0.0, 0.3, 1.0 };

GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };

GLfloat mat_shininess[] = { 128.0 };

glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);

glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);

glLightfv(GL_LIGHT1, GL_POSITION, light_position);

//glLightfv (GL_LIGHT1, GL_AMBIENT, ambient);

glLightfv (GL_LIGHT1, GL_SPECULAR, specular);

glLightfv (GL_LIGHT1, GL_DIFFUSE, diffuse);

// 指定全局环境光

glLightModelfv(GL_LIGHT_MODEL_AMBIENT,model_ambient);

glEnable(GL_LIGHTING);

glEnable(GL_LIGHT1);

glDepthFunc(GL_LEQUAL);

glEnable(GL_DEPTH_TEST);

glEnable(GL_AUTO_NORMAL);

glEnable(GL_NORMALIZE);

void CALLBACK reshape(GLsizei w, GLsizei h)

{

if (!h) return;

glViewport(0, 0, w, h);

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

if (w <= h)

glOrtho (-500.0, 500.0, -500.0*(GLfloat)h/(GLfloat)w,

500.0*(GLfloat)h/(GLfloat)w, -500, 500);

else

glOrtho (-500.0*(GLfloat)w/(GLfloat)h,

500.0*(GLfloat)w/(GLfloat)h, -500.0, 500.0, -500, 500);

glMatrixMode(GL_MODELVIEW);

}

void CALLBACK display(void)

{

glLoadIdentity();

glClear (GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);//清除背景

glRotated(nAngleX,1,0,0);

glRotated(nAngleY,0,1,0);

glRotated(nAngleZ,0,0,1);

glLineStipple(1, 0x3F07); // 指定点划格式

glEnable(GL_LINE_STIPPLE); // 进入点划模式

glBegin(GL_LINES);

// X轴：红

glColor3f (1.0, 0, 0);

glVertex3d(-490,0,0);

glVertex3d(490,0,0);

// Y轴：绿

glColor3f (0.0, 1.0, 0);

glVertex3d(0,-490,0);

glVertex3d(0,490,0);

// Z轴：蓝

glColor3f (0.0, 0.0, 1);

glVertex3d(0,0,-490);

glVertex3d(0,0,490);

glEnd();

glDisable(GL_LINE_STIPPLE);//离开点划模式

glColor3f (1.0, 0.0, 0);

glPushMatrix(); // 车体

glTranslatef(0,210,0);

auxSolidBox(600, 20, 400);

glPopMatrix();

glPushMatrix(); // 左前腿

glTranslatef(-260,100,180);

auxSolidBox(25, 200, 25);

glPopMatrix();

glPushMatrix(); // 左后腿

glTranslatef(-260,100,-180);

auxSolidBox(25, 200, 25);

glPopMatrix();

glPushMatrix(); // 右前腿

glTranslatef(260,100,180);

auxSolidBox(25, 200, 25);

glPopMatrix();

glPushMatrix(); // 右后腿

glTranslatef(260,100,-180);

auxSolidBox(25, 200, 25);

glPopMatrix();

glPushMatrix(); // 球

glTranslatef(-200,260,0);

auxSolidSphere(40);

glPopMatrix();

glPushMatrix(); // 八面体

glTranslatef(-200,260,160);

auxSolidOctahedron(40);

glPopMatrix();

glPushMatrix(); // 圆锥体

glTranslatef(-60,220,120);

glRotatef(-90,1,0,0);

auxSolidCone(60, 100);

glPopMatrix();

glPushMatrix(); //

glTranslatef(60,270,0);

glRotatef(40,0,1,0);

auxSolidTeapot(70);

glPopMatrix();

glPushMatrix(); //

glTranslatef(240,360,0);

auxSolidCylinder(40,140);

glPopMatrix();

auxSwapBuffers();

}

int _tmain(int argc, _TCHAR* argv[])

{

auxInitDisplayMode (AUX_DOUBLE | AUX_RGBA);

auxInitPosition (0, 0, 1000, 700);

auxInitWindow ("全局环境光");

myinit ();

auxKeyFunc (AUX_LEFT, ClockwiseRotateByY);

auxKeyFunc (AUX_RIGHT, CounterClockwiseRotateByY);

auxKeyFunc (AUX_UP, ClockwiseRotateByX);

auxKeyFunc (AUX_DOWN, CounterClockwiseRotateByX);

auxKeyFunc (AUX_D, ClockwiseRotateByZ);

auxKeyFunc (AUX_d, ClockwiseRotateByZ);

auxKeyFunc (AUX_U, CounterClockwiseRotateByZ);

auxKeyFunc (AUX_u, CounterClockwiseRotateByZ);

auxReshapeFunc(reshape);//回调函数

auxMainLoop(display);

return 0;

}

5.9 近视点和无穷远视点

在无穷远点的情况下，场景中所有顶点到视点的方向都相同。采用近视点时（local viewpoint），结果的真实感会更强，但需计算每个顶点的方向，因此总体性能将下降。

默认情况下，认为视点位于无穷远处，位置将影响镜面反射区计算，也就是说，顶点的镜面反射亮度取决于该顶点的法线、顶点相对于光源的方向和顶点相对于视点的方向。指定方法是：

glLightModeli(GL_LIGHT_MODEL_LOCAL_VIEWER , GL_TRUE) ;

上述代码把视点放在坐标系的（0 ，0 ，0 ）处，若把视点放到无穷远处，则执行如下代码

glLightModeli(GL_LIGHT_MODEL_LOCAL_VIEWER , GL_FALSE) ;

上述代码可在EP5-5中实现。

【综合示例EP5-6】场景中绘制一组静物模型，使用透视投影实现。

把实验五中的投影方式，由平行投影改为透视投影。转动场景时，物体显示会出现不正常。其中一个关键是要加入面剔除功能，第二个关键是对于茶壶而言，其面的定义是按顺时针的，这与一般物体的定义不同。下面的关键代码已用粗体标出。

#include "stdafx.h"

int nAngleY=0; // 沿Y轴旋转的角度

int nAngleX=0; // 沿X轴旋转的角度

int nAngleZ=0; // 沿Z轴旋转的角度

void CALLBACK ClockwiseRotateByX()

{

nAngleX--;

}

void CALLBACK CounterClockwiseRotateByX()

{

nAngleX++;

}

void CALLBACK ClockwiseRotateByZ()

{

nAngleZ--;

}

void CALLBACK CounterClockwiseRotateByZ()

{

nAngleZ++;

}

void CALLBACK ClockwiseRotateByY()

{

nAngleY--;

}

void CALLBACK CounterClockwiseRotateByY()

{

nAngleY++;

}

void myinit (void)

{

/* 将背景清为白色*/

glClearColor (0.0, 0.0,0.0, 1.0);

glClearDepth(1.0f); // 深度范围在【，】之间

glShadeModel (GL_SMOOTH);

// 光源属性值

GLfloat ambient[] = { 0.5, 0.0, 0.0, 1.0 };

GLfloat specular[] = { 1.0, 1.0, 0.0, 1.0 };

GLfloat diffuse[] = { 0.5, 0.5, 0.5, 1.0 };

GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };

// 材质属性值

GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };

GLfloat mat_shininess[] = { 128.0 };

// 设置材质

glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);

glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);

// 设置光源

glLightfv(GL_LIGHT1, GL_POSITION, light_position);

glLightfv (GL_LIGHT1, GL_AMBIENT, ambient);

glLightfv (GL_LIGHT1, GL_SPECULAR, specular);

glLightfv (GL_LIGHT1, GL_DIFFUSE, diffuse);

glEnable(GL_LIGHTING);

glEnable(GL_LIGHT1);

// 启动深度测试

glEnable(GL_DEPTH_TEST);

glDepthFunc(GL_LEQUAL);

// 启动自动法线

glEnable(GL_AUTO_NORMAL);

glEnable(GL_NORMALIZE);

// 启动面剔除功能

glEnable(GL_CULL_FACE); // 不渲染一些面的功能启动

glFrontFace(GL_CCW); // 指定正面的方向

glCullFace(GL_BACK); // 不渲染背面

}

void CALLBACK reshape(GLsizei w, GLsizei h)

{

if (!h) return;

glViewport(0, 0, w, h);

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

gluPerspective(60.0,w/h,1.0f,2000.0f);

glMatrixMode(GL_MODELVIEW);

glLoadIdentity();

}

void CALLBACK display(void)

{

glLoadIdentity();

glClear (GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);//清除背景

glTranslatef(0,0,-1200);

glRotated(nAngleX,1,0,0);

glRotated(nAngleY,0,1,0);

glRotated(nAngleZ,0,0,1);

glLineStipple(1, 0x3F07); // 指定点划格式

glEnable(GL_LINE_STIPPLE); // 进入点划模式

glBegin(GL_LINES);

// X轴：红

glColor3f (1.0, 0, 0);

glVertex3d(-490,0,0);

glVertex3d(490,0,0);

// Y轴：绿

glColor3f (0.0, 1.0, 0);

glVertex3d(0,-490,0);

glVertex3d(0,490,0);

// Z轴：蓝

glColor3f (0.0, 0.0, 1);

glVertex3d(0,0,-490);

glVertex3d(0,0,490);

glEnd();

glDisable(GL_LINE_STIPPLE);//离开点划模式glFrontFace(GL_CCW);

glColor3f (1.0, 0.0, 0);

glPushMatrix(); // 车体

glTranslatef(0,210,0);

auxSolidBox(600, 20, 400);

glPopMatrix();

glPushMatrix(); // 左前腿

glTranslatef(-260,100,180);

auxSolidBox(25, 200, 25);

glPopMatrix();

glPushMatrix(); // 左后腿

glTranslatef(-260,100,-180);

auxSolidBox(25, 200, 25);

glPopMatrix();

glPushMatrix(); // 右前腿

glTranslatef(260,100,180);

auxSolidBox(25, 200, 25);

glPopMatrix();

glPushMatrix(); // 右后腿

glTranslatef(260,100,-180);

auxSolidBox(25, 200, 25);

glPopMatrix();

glPushMatrix(); // 球

glTranslatef(-200,360,0);

auxSolidSphere(40);

glPopMatrix();

glPushMatrix(); // 八面体

glTranslatef(-200,360,160);

auxSolidOctahedron(40);

glPopMatrix();

glPushMatrix(); // 圆锥体

glTranslatef(-60,300,120);

glRotatef(-90,1,0,0);

auxSolidCone(60, 100);

glPopMatrix();

glFrontFace(GL_CW);

glPushMatrix(); //

glTranslatef(60,300,0);

glRotatef(40,0,1,0);

auxSolidTeapot(70);

glPopMatrix();

glFrontFace(GL_CCW);

glPushMatrix(); //

glTranslatef(240,362,0);

auxSolidCylinder(40,140);

glPopMatrix();

auxSwapBuffers();

}

int _tmain(int argc, _TCHAR* argv[])

{

auxInitDisplayMode (AUX_DOUBLE | AUX_RGBA|AUX_DEPTH);

auxInitPosition (0, 0, 1000, 700);

auxInitWindow ("透视投影下的光照");

myinit ();

auxKeyFunc (AUX_LEFT, ClockwiseRotateByY);

auxKeyFunc (AUX_RIGHT, CounterClockwiseRotateByY);

auxKeyFunc (AUX_UP, ClockwiseRotateByX);

auxKeyFunc (AUX_DOWN, CounterClockwiseRotateByX);

auxKeyFunc (AUX_D, ClockwiseRotateByZ);

auxKeyFunc (AUX_d, ClockwiseRotateByZ);

auxKeyFunc (AUX_U, CounterClockwiseRotateByZ);

auxKeyFunc (AUX_u, CounterClockwiseRotateByZ);

auxReshapeFunc(reshape);//回调函数

auxMainLoop(display);

return 0;

}

5.10材质

OpenGL用材料对光的红、绿、蓝三原色的反射率来近似定义材料的颜色。象光源一样，材料颜色也分成环境、漫反射和镜面反射成分，它们决定了材料对环境光、漫反射光和镜面反射光的反射程度（或者说成反射系数与前面的理论对应）。

在进行光照计算时，材料对环境光的反射率与每个进入光源的环境光相乘，对漫反射光的反射率与每个进入光源的漫反射光相乘，对镜面光的反射率与每个进入光源的镜面反射光相乘。对环境光与漫反射光的反射程度决定了材料的颜色，对镜面反射光的反射率通常是白色或灰色。镜面反射高光最亮的地方将变成具有光源镜面光强度的颜色。例如一个光亮的红色塑料球，球的大部分表现为红色，光亮的高光将是白色的。

5.10.1 材质RGB值和光源RGB值的关系

对于光源，R、G、B值等于R、G、B对其最大强度的百分比。若光源颜色的R、G、B值都是1.0，则是最强的白光；若值变为0.5，颜色仍为白色，但强度为原来的一半，于是表现为灰色；若R＝G＝1.0，B＝0.0，则光源为黄色。

对于材质，R、G、B值为材质对光的R、G、B成分的反射率。比如，一种材质的R＝1.0、G＝0.5、B＝0.0，则材质反射全部的红色成分，一半的绿色成分，不反射蓝色成分。也就是说，若OpenGL的光源颜色为（LR、LG、LB），材质颜色为（MR、MG、MB），那么，在忽略所有其他反射效果的情况下，最终到达眼睛的光的颜色为（LR*MR、LG*MG、LB*MB）。

对于两束光，相应的值分别为（R1、G1、B1）和（R2、G2、B2），则OpenGL将各个颜色成分相加，得到（R1+R2、G1+G2、B1+B2），若任一成分的和值大于1（超出了设备所能显示的亮度）则约简到1.0。

5.10.2 材质定义

材质的定义与光源的定义类似。其函数为：

void glMaterial{if}[v](GLenum face,GLenum pname,TYPE param);

定义光照计算中用到的当前材质。face可以是GL_FRONT、GL_BACK、GL_FRONT_AND_BACK，它表明当前材质应该应用到物体的哪一个面上；pname说明一个特定的材质；param是材质的具体数值，若函数为向量形式，则param是一组值的指针，反之为参数值本身。非向量形式仅用于设置GL_SHINESS。pname参数值具体内容见表5-2。另外，参数GL_AMBIENT_AND_DIFFUSE表示可以用相同的RGB值设置环境光颜色和漫反射光颜色。GL_SHINESS值介于[0,128]之间，值越大，光斑越小，越集中。

表5-2 材质参数介绍

【综合示例EP5-7】材质的综合示例。

#include"stdafx.h"

int nAngleY=0; // 沿Y轴旋转的角度int nAngleX=0; // 沿X轴旋转的角度int nAngleZ=0; // 沿Z轴旋转的角度

void CALLBACK ClockwiseRotateByX()

{

nAngleX--;

}

void CALLBACK CounterClockwiseRotateByX() {

nAngleX++;

}

void CALLBACK ClockwiseRotateByZ()

{

nAngleZ--;

}

void CALLBACK CounterClockwiseRotateByZ() {

nAngleZ++;

}

void CALLBACK ClockwiseRotateByY()

{

nAngleY--;

}

void CALLBACK CounterClockwiseRotateByY() {

nAngleY++;

}

void myinit (void)

{

/* 将背景清为白色*/

glClearColor (0.0, 0.0,0.0, 1.0);

glShadeModel (GL_SMOOTH);

GLfloat ambient[] = { 0.0, 0.0, 0.0, 1.0 };

GLfloat specular[] = { 1.0, 1.0, 0.0, 1.0 };

GLfloat diffuse[] = { 1.0, 1.0, 1.0, 1.0 };

GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };

GLfloat lmodel_ambient[] = { 0.4, 0.4, 0.4, 1.0 };

GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };

GLfloat mat_shininess[] = { 128.0 };

glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);

glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);

glLightfv(GL_LIGHT1, GL_POSITION, light_position);

glLightfv (GL_LIGHT1, GL_AMBIENT, ambient);

glLightfv (GL_LIGHT1, GL_SPECULAR, specular);

glLightfv (GL_LIGHT1, GL_DIFFUSE, diffuse);

// 指定全局环境光

glLightModelfv(GL_LIGHT_MODEL_AMBIENT, lmodel_ambient);

// 指定视点:GL_TRUE:视点位于（，，），GL_FALSE：视点在无穷远glLightModeli(GL_LIGHT_MODEL_LOCAL_VIEWER, GL_FALSE);

glEnable(GL_LIGHTING);

glEnable(GL_LIGHT1);

glDepthFunc(GL_LEQUAL);

glEnable(GL_DEPTH_TEST);

glEnable(GL_AUTO_NORMAL);

glEnable(GL_NORMALIZE);

}

void CALLBACK reshape(GLsizei w, GLsizei h)

{

if (!h) return;

glViewport(0, 0, w, h);

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

if (w <= h)

glOrtho (-500.0, 500.0, -500.0*(GLfloat)h/(GLfloat)w,

500.0*(GLfloat)h/(GLfloat)w, -500, 500);

else

glOrtho (-500.0*(GLfloat)w/(GLfloat)h,

500.0*(GLfloat)w/(GLfloat)h, -500.0, 500.0, -500, 500);

glMatrixMode(GL_MODELVIEW);

}

void CALLBACK 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[] = { 0.0, 0.8, 0.0, 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};

glLoadIdentity();

glClear (GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);//清除背景

glRotated(nAngleX,1,0,0);

glRotated(nAngleY,0,1,0);

glRotated(nAngleZ,0,0,1);

glLineStipple(1, 0x3F07); // 指定点划格式

glEnable(GL_LINE_STIPPLE); // 进入点划模式

glBegin(GL_LINES);

// X轴：红

glColor3f (1.0, 0, 0);

glVertex3d(-490,0,0);

glVertex3d(490,0,0);

// Y轴：绿

glColor3f (0.0, 1.0, 0);

glVertex3d(0,-490,0);

glVertex3d(0,490,0);

// Z轴：蓝

glColor3f (0.0, 0.0, 1);

glVertex3d(0,0,-490);

glVertex3d(0,0,490);

glEnd();

glDisable(GL_LINE_STIPPLE);//离开点划模式

/* (1,1) draw sphere in first row, first column

* diffuse reflection only; no ambient or specular

*/

glPushMatrix();

glTranslatef (-375, 300, 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, no_mat);

auxSolidSphere(100.0);

glPopMatrix();

/* (1,2) draw sphere in first row, second column

* diffuse and specular reflection; low shininess; no ambient

*/

glPushMatrix();

glTranslatef (-125, 300.0, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (1,3) draw sphere in first row, third column

* diffuse and specular reflection; high shininess; no ambient

*/

glPushMatrix();

glTranslatef (125, 300.0, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (1,4) draw sphere in first row, fourth column

* diffuse reflection; emission; no ambient or specular reflection */

glPushMatrix();

glTranslatef (375, 300.0, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (2,1) draw sphere in second row, first column

* ambient and diffuse reflection; no specular

*/

glPushMatrix();

glTranslatef (-375, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (2,2) draw sphere in second row, second column

* ambient, diffuse and specular reflection; low shininess

*/

glPushMatrix();

glTranslatef (-125, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (2,3) draw sphere in second row, third column

* ambient, diffuse and specular reflection; high shininess */

glPushMatrix();

glTranslatef (125, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (2,4) draw sphere in second row, fourth column

* ambient and diffuse reflection; emission; no specular

*/

glPushMatrix();

glTranslatef (375, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (3,1) draw sphere in third row, first column

* colored ambient and diffuse reflection; no specular

*/

glPushMatrix();

glTranslatef (-375, -300.0, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (3,2) draw sphere in third row, second column

* colored ambient, diffuse and specular reflection; low shininess */

glPushMatrix();

glTranslatef (-125, -300.0, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (3,3) draw sphere in third row, third column

* colored ambient, diffuse and specular reflection; high shininess */

glPushMatrix();

glTranslatef (125, -300.0, 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);

auxSolidSphere(100.0);

glPopMatrix();

/* (3,4) draw sphere in third row, fourth column

* colored ambient and diffuse reflection; emission; no specular */

glPushMatrix();

glTranslatef (375, -300.0, 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);

auxSolidSphere(100.0);

glPopMatrix();

auxSwapBuffers();

}

int _tmain(int argc, _TCHAR* argv[])

{

auxInitDisplayMode (AUX_DOUBLE | AUX_RGBA|AUX_DEPTH);

auxInitPosition (0, 0, 1000, 700);

auxInitWindow ("材质示例");

myinit ();

auxKeyFunc (AUX_LEFT, ClockwiseRotateByY);

auxKeyFunc (AUX_RIGHT, CounterClockwiseRotateByY);

auxKeyFunc (AUX_UP, ClockwiseRotateByX);

auxKeyFunc (AUX_DOWN, CounterClockwiseRotateByX);

auxKeyFunc (AUX_D, ClockwiseRotateByZ);

auxKeyFunc (AUX_d, ClockwiseRotateByZ);

auxKeyFunc (AUX_U, CounterClockwiseRotateByZ);

auxKeyFunc (AUX_u, CounterClockwiseRotateByZ);

auxReshapeFunc(reshape);//回调函数

auxMainLoop(display);

return 0;

}

5.10.3 颜色材质模式

glMaterial*函数改变材质时开销较大，因此建议最好尽可能少的改变材质，以减少改变材质时所带来的性能开销，可采用另一种方式即改变材质颜色，相应函数为glColorMaterial()，说明如下：

void glColorMaterial(GLenum face,GLenum mode);

函数参数face指定面，值有GL_FRONT、GL_BACK或GL_FRONT_AND_BACK（缺省值）。mode指定材质成分，值有GL_AMBIENT、GL_DIFFUSE、GL_AMBIENT_AND_DIFFUSE（缺省值）、GL_SPECULAR或GLEMISSION。

注意：这个函数说明了两个独立的值，第一个参数说明哪一个面和哪些面被修改，而第二个参数说明这些面的哪一个或哪些材质成分要被修改。OpenGL并不为每一种face保持独立的mode变量。在调用glColorMterial()以后，首先需要用GL_COLOR_MATERIAL作为参数调用glEnable()来启动颜色材质，然后在绘图时调用glColor*()来改变当前颜色，或用glMaterial()来改变材质成分。当不用这种方式来改变材质时，可调用glDisable(GL_COLOR_MA TERIAL)来关闭取消。如下面一段代码：

glColorMaterial(GL_FRONT,GL_DIFFUSE);

glEnable(GL_COLOR_MATERIAL);

glColor3f(0.3,0.5,0.7);

/* draw some objects here. */

glcolor3f(0.0,1.0,0.0);

/* draw other objects here.*/

glDisable(GL_COLOR_MATERIAL);

当需要改变场景中大部分物体的单个材质时，最好调用glColorMaterial()；当需要修改不止一个材质参数时，最好调用glMaterial*()。注意，当不需要颜色材质时一定要关闭它，以避免相应的开销。

注：该函数指定的不是光的强度，而是物体对光的反射率。如上例中指定了颜色材质的散射光属性，则下面的glColor3f(0.3,0.5,0.7)是说明了对散射光的R、G、B的反射率！此时还需要光源的散射光强度，二者缺一不可！

【综合示例EP5-8】使用glColorMterial（）函数改变材质的散射光属性。按下鼠标的左键修改散射光颜色的红色分量，按下鼠标的中间键修改散射光颜色的绿色分量，按下鼠标的右键修改散射光颜色的蓝色分量，

完整的程序代码如下，粗体部分为新加入的代码。

#include"stdafx.h"

int nAngleY=0; // 沿Y轴旋转的角度

int nAngleX=0; // 沿X轴旋转的角度

int nAngleZ=0; // 沿Z轴旋转的角度

GLfloat diffuseMaterial[] = { 0.5, 0.5, 0.5, 1.0 };

void CALLBACK leftbutton (AUX_EVENTREC *event) {

diffuseMaterial[0] += 0.1;

if (diffuseMaterial[0] > 1.0)

diffuseMaterial[0] = 0.0;

}

void CALLBACK rightbutton (AUX_EVENTREC *event) {

diffuseMaterial[2] += 0.1;

if (diffuseMaterial[2] > 1.0)

diffuseMaterial[2] = 0.0;

}

void CALLBACK middlebutton (AUX_EVENTREC *event) {

diffuseMaterial[1] += 0.1;

if (diffuseMaterial[1] > 1.0)

diffuseMaterial[1] = 0.0;

}

void CALLBACK ClockwiseRotateByX()

{

nAngleX--;

}

void CALLBACK CounterClockwiseRotateByX()

{

nAngleX++;

}

void CALLBACK ClockwiseRotateByZ()

{

nAngleZ--;

}