OpenGL编程轻松入门之特殊效果操作

　2007-05-06 19:58:27　来源：WEB开发网　　　

核心提示：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，OpenGL编程轻松入门之特殊效果操作，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，dfactor指定红，绿，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

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(w<h)
　　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);
}