GLUT Tutorials 8: GLUT子菜单

博客转自：https://www.cnblogs.com/yangxi/archive/2011/09/16/2178507.html

前一章我们知道了怎么建立简单的菜单，现在我们来看看怎样来添加一个级联的子菜单。子菜单的建立和我们前面用的建立菜单的函数一样。建立菜单后我们把子菜单作为一个条目添加进去。使用函数glutAddSubMenu来完成这项工作：

void glutAddSubMenu(char *entryName，int menuIndex)；
参数：
entryName：子菜单名称。
menuIndex：子菜单索引，这个就是我们调用glutCreateMenu来创建子菜单返回的值。

上面就是添加子菜单的函数。下面是一小段代码，说明上面函数的用处的。

void createGLUTMenus() {
 
         int menu,submenu;
 
         submenu = glutCreateMenu(processMenuEvents);
         glutAddMenuEntry("Red",RED);
         glutAddMenuEntry("Blue",BLUE);
         glutAddMenuEntry("Green",GREEN);
 
         menu = glutCreateMenu(processMenuEvents);
         glutAddMenuEntry("White",WHITE);
         glutAddSubMenu("RGB Menu",submenu);
         glutAttachMenu(GLUT_RIGHT_BUTTON);
}

注意这里处理菜单事件的函数，对菜单和子菜单都是一样的，你可以自己写个处理子菜单事件的函数。完整代码如下

#include <gl/glut.h>

#define RED 1
#define GREEN 2
#define BLUE 3
#define WHITE 4

//所有的变量被初始化为1，表明三角形最开始是白色的。
float red = 1.0, blue = 1.0, green = 1.0;
static float angle = 0.0, angleX = 0.0, ratio;
// initially define the increase of the angle by 0.05;
float deltaAngle = 0.05;

void renderScene(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glPushMatrix();
    glRotatef(angle, 0.0, 1.0, 0.0);
    glRotatef(angleX, 1.0, 0.0, 0.0);
    glColor3f(red, green, blue);

    glBegin(GL_TRIANGLES);
    glVertex3f(-0.5, -0.5, 0.0);
    glVertex3f(0.5, 0.0, 0.0);
    glVertex3f(0.0, 0.5, 0.0);
    glEnd();
    glPopMatrix();
    // this is the new line
    // previously it was: angle++;
    angle += deltaAngle;
    glutSwapBuffers();
}

void reShape(int w, int h)
{
    // 防止被0除.
    if (h == 0)
        h = 1;

    ratio = 1.0f * w / h;
    //Reset the coordinate system before modifying
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    //设置视口为整个窗口大小
    glViewport(0, 0, w, h);

    //设置可视空间
    gluPerspective(45, ratio, 1, 1000);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(0.0, 0.0, 5.0, 0.0, 0.0, -1.0, 0.0f, 1.0f, 0.0f);
}

void processMenuEvents(int option) 
{
    //option，就是传递过来的value的值。
    switch (option) {
    case RED:
        red = 1.0;
        green = 0.0;
        blue = 0.0; break;
    case GREEN:
        red = 0.0;
        green = 1.0;
        blue = 0.0; break;
    case BLUE:
        red = 0.0;
        green = 0.0;
        blue = 1.0; break;
    case WHITE:
        red = 1.0;
        green = 1.0;
        blue = 1.0; break;
    }
}

void createGLUTMenus()
{
    int menu, submenu;

    submenu = glutCreateMenu(processMenuEvents);
    glutAddMenuEntry("Red", RED);
    glutAddMenuEntry("Blue", BLUE);
    glutAddMenuEntry("Green", GREEN);

    menu = glutCreateMenu(processMenuEvents);
    glutAddMenuEntry("White", WHITE);
    glutAddSubMenu("RGB Menu", submenu);
    glutAttachMenu(GLUT_RIGHT_BUTTON);
}

void main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(320, 320);
    glutCreateWindow("GLUT Tutorial Menu");
    glutDisplayFunc(renderScene);
    glutIdleFunc(renderScene);
    glutReshapeFunc(reShape);

    //调用我们的函数来创建菜单
    createGLUTMenus();

    glutMainLoop();
}

显示效果如下