xcode – OpenGL深度问题

以下代码是发生问题的代码的简单示例.它在同一个地方渲染出2个梯形,其中一个旋转.但旋转的一个总是显示在顶部,即使旋转时应该在第一个梯形后面.

我想我通过初始化OpenGL搞砸了一些东西.此外,当搜索stackoverflow时,我发现有人建议执行以下代码并查看输出的帖子.

int depth;
glGetIntegerv(GL_DEPTH_BITS,&depth);
printf("%i bits depth",depth);

好的输出是,0位深度,这是不好我猜:(

我正在使用glfw库在xCode上开发Mac

#include <GL/glfw.h>
#include <stdlib.h>

int main( void )
{
   int running = GL_TRUE;

   if( !glfwInit() )
   {
      exit( EXIT_FAILURE );
   }

   // Open an OpenGL window
   if( !glfwOpenWindow( 640,480,GLFW_WINDOW ))
   {
      glfwTerminate();
      exit( EXIT_FAILURE );
   }

   glEnable(GL_DEPTH_TEST);

   float angle = 0;

   // Main loop
   while( running )
   {

      double elapsedTime = glfwGetTime();
      glfwSetTime(0);
      angle += 90 * elapsedTime;

      // OpenGL rendering goes here...
      glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

      glMatrixMode(GL_MODELVIEW);
      glLoadIdentity();

      glPushMatrix(); //Save the transformations performed thus far
      glColor3f(1.0f,1.0,0.0);
      glTranslatef(0.0f,0.0f,0.0f); //Move to the center of the trapezoid
      //glRotatef(angle,1.0f,0.0f); //Rotate about the y-axis
      glBegin(GL_QUADS);

      //Trapezoid
      glVertex3f(-0.7f,-0.5f,0.0f);
      glVertex3f(0.7f,0.0f);
      glVertex3f(0.4f,0.5f,0.0f);
      glVertex3f(-0.4f,0.0f);

      glEnd();

      glPopMatrix();

      glPushMatrix(); //Save the transformations performed thus far
      glColor3f(1.0f,0.0,0.0f); //Move to the center of the trapezoid
      glRotatef(angle,0.0f);

      glEnd();

      glPopMatrix(); //Undo the move to the center of the trapezoid

      glfwSwapBuffers();

      // Check if ESC key was pressed or window was closed
      running = !glfwGetKey( GLFW_KEY_ESC ) &&
      glfwGetWindowParam( GLFW_OPENED );
   }

   // Close window and terminate GLFW
   glfwTerminate();
   // Exit program
   exit( EXIT_SUCCESS );
}