OpenGL之特殊效果处理.docVIP

　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(0.0,0.0,1.0,0.5);　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