opengl 云

透明效果的话，先用glEnable(GL_BLEND)开启混合功能，设置模式，比如glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA)，代表把源颜色乘alpha值，目标颜色乘（1-alpha）值，然后设置物体的alpha值即可。
举个例子
#include<gl/glut.h>
void myDisplay()
{
glClear(GL_COLOR_BUFFER_BIT);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
glColor4f(1,0,0,0.8);
glRectf(-1,-1,0.5,0.5);
glColor4f(0,1,0,0.6);
glRectf(-0.5,-0.5,1,1);
glutSwapBuffers();
}

int main(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);
glutInitWindowPosition(200, 200);
glutInitWindowSize(500, 500);
glutCreateWindow("旋转四面体");
glutDisplayFunc(&myDisplay);
glutMainLoop();
return 0;
}