为什么我的VAO不起作用？

Question

最近，我正在学习OpenGL编程。但是，当我想使用VAO实现样本时。它不像红皮书中所说的那样有效。

下面是我的代码。我创建了两个对象（一个四边形和一个三角形）。然后为每个对象使用一个vAO。但是在display（）函数中，我无法通过调用glBindVertexArray（）和glDrawElements（）来绘制特定对象。

#define GL_GLEXT_PROTOTYPES
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glx.h>
#include <GL/glut.h>
#include <stdio.h>

#define VERTICES 0
#define INDICES 1
#define NUM_BUFFERS 2
#define BUFFER_OFFSET(bytes) ((GLubyte*) NULL + (bytes))


static GLfloat spin = 0.0;


GLfloat vertices[][2] =
{

    {-25.0, -25.0},
    {-25.0, 25.0},
    {25.0, -25.0},
    {25.0, 25.0}
};
GLfloat vertices2[][2] =
{

    {-25.0, -25.0},
    {-25.0, 25.0},
    {25.0, -25.0}
};
GLubyte indices[4] = {1,0, 2, 3};
GLubyte indices2[3] = {1, 0, 2};
enum { qua, tri};
GLuint VAO[2];
GLenum PrimType[2];
GLsizei NumElements[2];



void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glPushMatrix();
    glRotatef(spin, 0.0, 0.0, 1.0);
    //just draw the quad for testing
    glBindVertexArray(VAO[qua]);
    glDrawElements(PrimType[qua], NumElements[qua], GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));
    glPopMatrix();
    glFlush();
    glutSwapBuffers();
}

void spinDisplay(void)
{
    spin = spin + 2.0;
    if (spin > 360.0)
        spin = spin - 360.0;
    display();
}


void myinit(void)
{

    glClearColor(0.0, 0.0, 0.0, 1.0);
    glColor3f(1.0, 1.0, 1.0);
    glShadeModel(GL_FLAT);

    GLuint buffers[NUM_BUFFERS];
    GLuint buffers2[NUM_BUFFERS];

    //quad
    glGenVertexArrays(1, &VAO[qua]);
    {
    glBindVertexArray(VAO[qua]);
    glEnableVertexAttribArray(0);
    glGenBuffers(NUM_BUFFERS, buffers);
    glBindBuffer(GL_ARRAY_BUFFER, buffers[VERTICES]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexPointer(2, GL_FLOAT, 0, BUFFER_OFFSET(0));;
    glEnableClientState(GL_VERTEX_ARRAY);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, buffers[INDICES]);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
    PrimType[qua] = GL_QUADS;
    NumElements[qua] = sizeof(indices) / sizeof(indices[0]);
    glBindVertexArray(0);
    }

    //triangle
    glGenVertexArrays(1, &VAO[tri]);
    {
    glBindVertexArray(VAO[tri]);
    glEnableVertexAttribArray(0);
    glGenBuffers(NUM_BUFFERS, buffers2);
    glBindBuffer(GL_ARRAY_BUFFER, buffers2[VERTICES]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices2), vertices2, GL_STATIC_DRAW);
    glVertexPointer(2, GL_FLOAT, 0, BUFFER_OFFSET(0));
    glEnableClientState(GL_VERTEX_ARRAY);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, buffers2[INDICES]);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices2), indices2, GL_STATIC_DRAW);
    PrimType[tri] = GL_TRIANGLES;
    NumElements[tri] = sizeof(indices2) / sizeof(indices2[0]);
    }

}

void myReshape(GLsizei w, GLsizei h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    if (w <= h) 
        glOrtho (-50.0, 50.0, -50.0*(GLfloat)h/(GLfloat)w, 
            50.0*(GLfloat)h/(GLfloat)w, -1.0, 1.0);
    else 
        glOrtho (-50.0*(GLfloat)w/(GLfloat)h, 
            50.0*(GLfloat)w/(GLfloat)h, -50.0, 50.0, -1.0, 1.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity ();
}



int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(500, 500);
    glutInitWindowSize(300, 300);
    glutCreateWindow("double buffer");
    myinit();
    glutIdleFunc(spinDisplay);
    glutReshapeFunc(myReshape);
    glutMainLoop();
}