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每个物体在不同的环境在会有不同的视觉效果。为了使效果更加真实需要增加特殊效果。

例8：绘制三个互相重叠的矩形，这三个矩形从左到右分别为绿、红、蓝。其中红色、蓝色矩形的透明度分别为50%的透明度，即alpha值为0.5，如图九所示。

#include stdlib.h

#include GL/glut.h

void myInit(void)

{

glClearColor(0.2,0.8,0.8,0.0);//将背景设置为湖蓝色

glEnable(GL_BLEND);//激活GL_BLEND

glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);//指定像素的数学算法

glEnable(GL_FLAT);

}

void myDisplay(void)

{

glClear(GL_COLOR_BUFFER_BIT);

/*绘制一个绿色的矩形 alpha = 1.0*/

glColor4f(0.0,1.0,0.0,1.0);

glBegin(GL_POLYGON);

glVertex3f(-0.75,0.5,0.0);

glVertex3f(-0.75,-0.75,0.0);

glVertex3f(0.5,-0.75,0.0);

glVertex3f(0.5,0.5,0.0);

glEnd();

/*绘制一个红色的矩形 alpha = 0.5*/

glColor4f(1.0,0.0,0.0,0.5);

glBegin(GL_POLYGON);

glVertex3f(-0.25,1.0,0.0);

glVertex3f(-0.25,-0.25,0.0);

glVertex3f(1.0,-0.25,0.0);

glVertex3f(1.0,1.0,0.0);

glEnd();

/*绘制一个蓝色的矩形 alpha = 0.5*/

glColor4f(0.0,0.0,1.0当地时间30日下午4时许,0.5);

glBegin(GL_POLYGON);

glVertex3f(0.25,1.5,0.0);

glVertex3f(0.25,0.25,0.0);

glVertex3f(1.5,0.25,0.0);

glVertex3f(1.5,1.5,0.0);

glEnd();

glFlush();

}

void myReshape(int w,int h)

{

glViewport(0,0,w,h);

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

if(wh)

glOrtho(-1.5,1.5,-1.5*(GLfloat)h/(GLfloat)w,1.5*(GLfloat)h/(GLfloat)w,-1.5,1.5);

else

glOrtho(-1.5*(GLfloat)w/(GLfloat)h,1.5*(GLfloat)w/(GLfloat)h,-1.5,1.5,-1.5,1.5);

glMatrixMode(GL_MODELVIEW);

glLoadIdentity();

glTranslatef(-0.4,0.0,0.0);

}

int main(int argc,char ** argv)

{

/*初始化*/

glutInit(argc,argv);

glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);

glutInitWindowSize(300,400);

glutInitWindowPosition(200,200);

/*创建窗口*/

glutCreateWindow("BLEND POLYGON");

/*绘制与显示*/

myInit();

glutReshapeFunc(myReshape);

glutDisplayFunc(myDisplay);

/*进入GLUT事件处理循环*/

glutMainLoop();

return(0);

}

图九：三个互相重叠的矩形

·glBlendFunc（GLenum sfactor，GLenum dfactor） 指定像素算法。sfactor指定红，绿，蓝及alpha源混合因素是如何计算的。dfactor指定红，绿，蓝及alpha目标混合因素是如何计算的。

例9：绘制一个被雾化的圆锥体，如图十所示，为了观察不同的雾化参数，程序中加入了键盘操作。"shift+1"，" shift+2"键分别增加和减弱雾化浓度，"shift+3"设置雾化的起始点和终止点，"shift+4"和"shift+5"键改变雾化方程，"shift+6"将雾化颜色由白改为绿色，如图十一所示。

#include stdlib.h

#include GL/glut.h

GLfloat light_ambient[] = {0.1,0.1,0.1,0.0};

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

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

GLfloat light_position[] = {-10.0,0.0,5.0,0.0};

GLfloat material_ambient[] = {0.1745,0.01175,0.01175};

GLfloat material_diffuse[] = {0.61424,0.04136,0.04136};

GLfloat material_specular[] = {0.727811,0.626959,0.62659};

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

GLfloat fogColorGreen[] = {0.0,1.0,0.0,1当前应高度重视投资效益和经济增长质量我的钢铁.0};

float fogDensity = 0.02;

void myInit(void)

{

/*设置背景色*/

glClearColor(0.5,0.5,0.5,1.0);

/*设置光照*/

glLightfv(GL_LIGHT0,GL_AMBIENT,light_ambient);

glLightfv(GL_LIGHT0,GL_DIFFUSE,light_diffuse);

glLightfv(GL_LIGHT0,GL_SPECULAR,light_specular);

glLightfv(GL_LIGHT0,GL_POSITION,light_position);

/*设置材质*/

glMaterialfv(GL_FRONT,GL_AMBIENT,material_ambient);

glMaterialfv(GL_FRONT,GL_DIFFUSE,material_diffuse);

glMaterialfv(GL_FRONT,GL_SPECULAR,material_specular);

glMaterialf(GL_FRONT,GL_SHININESS,0.6*128);

glShadeModel(GL_SMOOTH);

glEnable(GL_DEPTH_TEST);

glDepthFunc(GL_LESS);

glEnable(GL_LIGHTING);

glEnable(GL_LIGHT0);

glEnable(GL_AUTO_NORMAL);

glEnable(GL_NORMALIZE);

glFrontFace(GL_CW);

/*设置雾化*/

glEnable(GL_FOG);

glFogi(GL_FOG_MODE,GL_LINEAR);

glFogfv(GL_FOG_COLOR,fogColorWhite);

glFogf(GL_FOG_DENSITY,fogDensity);

glFogf(GL_FOG_START,0.0);

glFogf(GL_FOG_END,15.0);

glHint(GL_FOG_HINT,GL_DONT_CARE);

}

/*根据不同的键值设置不同的雾化效果*/

static void myKey(unsigned char key,int x,int y)

{

switch(key)

{

case 33: //shift+1

fogDensity *= 1.10;

glFogi(GL_FOG_MODE,GL_EXP);

glFogf(GL_FOG_DENSITY,fogDensity);

glutPostRedisplay();

break;

case 64: //shift+2

fogDensity /= 1.10;

glFogi(GL_FOG_MODE,GL_EXP);

glFogf(GL_FOG_DENSITY,fogDensity);

glutPostRedisplay();

break;

case 35: //shift+3

glFogi(GL_FOG_START,0.0);

glFogi(GL_FOG_END,8.0);

glutPostRedisplay();

break;

case 36: //shift+4

glFogi(GL_FOG_MODE,GL_EXP2);

glutPostRedisplay();

break;

case 37: //shift+5

glFogi(GL_FOG_MODE,GL_LINEAR);

glutPostRedisplay();

break;

case 94: //shift+6

glFogfv(GL_FOG_COLOR,fogColorGreen);

glutPostRedisplay();

break;

case 27: //Esc

exit(0);

default:

break;

}

}

/*绘制圆锥体*/

void myDisplay(void)

{

glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

glPushMatrix();

glTranslatef(-4.0,4.0,0.0);

glRotatef(30.0,1.0,1.0,0.0);

glutSolidCone(1.0,50.0,20.0,20.0);

glPopMatrix();

glutSwapBuffers();

}

void myReshape(int w,int h)

{

glViewport(0,0,(GLsizei)w,(GLsizei)h);

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

gluPerspective(100.0,1.0,1.0,20.0);

glMatrixMode(GL_MODELVIEW);

glLoadIdentity();

glTranslatef(0.0,0.0,-15.5);

}

int main(int argc,char ** argv)

{

/*初始化*/

glutInit(argc,argv);

glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB|GLUT_DEPTH);

glutInitWindowSize(300,300);

glutInitWindowPosition(100,100);

/*创建窗口*/

glutCreateWindow(" FOG ");

/*绘制与显示*/

myInit();

glutKeyboardFunc(myKey);

glutReshapeFunc(myReshape);

glutDisplayFunc(myDisplay);

/*进入GLUT事件处理循环*/

glutMainLoop();

return 0;

}

图十：被雾化的圆锥体

·glFog指定雾化参数。后面不同的字母表明参数的数据类型。f表示float，i表示integer，v表示vector，也就是表明一个指针。

GL_FOG_MODE是一个单值整数或浮点数，该数值指定了用来计算雾化融合因子f的方程。

GL_DENSITY 是一个单值整数或浮点数，该值指定雾化浓度。

GL_FOG_START 是一个单值整数或浮点数，该值指定雾化的起始值。

GL_FOG_END是一个单值整数或浮点数，该值指定雾化的终止值。

GL_FOG_INDEX是一个单值整数或浮点数，该值指定雾化索引值if，缺省的雾化索引值为0.0。

GL_FOG_COLOR包含4个整数值或浮点数值，这些数值指定的是雾化颜色Cf，整数值进行线性映射。

·glHint指定实现的线索。本例中GL_FOG_HINT指定雾化计算精度。GL_DONT_CARE指对选项不做考虑。

图十一：雾化为绿色的圆锥体

本例中还涉及到键盘操作，glutKeyboardFun。此函数注册当前窗口的键盘回调函数。因为这不是本节的主要内容，我们只简单提一下。此函数的原形为void glutKeyboardFunc （void（*func）（unsigned char key，int x，int y））所以我们自己写的回调函数必须按照原形上规定的写。查看本文来源

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