C++ code>glFlush与glutSwapBuffers。这将导致display（）

注意：glutSwapBuffers将只在GL应用程序是双缓冲的情况下执行我描述的操作。当应用程序初始化GL时，除非有充分的理由，否则应始终请求双缓冲。您的应用程序不请求双缓冲。您需要将

main（）

中对

glutInitDisplayMode（GLUT_RGBA）

的调用替换为`glutIinit

，即使它运行得很快，也会显示一个窗口，直到您关闭它或按0x33键退出。尝试在调试程序中运行谢谢，将在datenwolf中运行

// Two-Dimensional Sierpinski Gasket
// Generated using randomly selected vertices and bisection

#include "Angel.h"

const int NumPoints = 5000;

//----------------------------------------------------------------------------

void
init( void )
{
    vec2 points[NumPoints];

    // Specifiy the vertices for a triangle
    vec2 vertices[3] = {
        vec2( -1.0, -1.0 ), vec2( 0.0, 1.0 ), vec2( 1.0, -1.0 )
    };

    // Select an arbitrary initial point inside of the triangle
    points[0] = vec2( 0.25, 0.50 );

    // compute and store N-1 new points
    for ( int i = 1; i < NumPoints; ++i ) {
        int j = rand() % 3;   // pick a vertex at random

        // Compute the point halfway between the selected vertex
        //   and the previous point
        points[i] = ( points[i - 1] + vertices[j] ) / 2.0;
    }

    // Create a vertex array object
    GLuint vao[1];
    glGenVertexArraysAPPLE( 1, vao );
    glBindVertexArrayAPPLE( vao[0] );


    // Create and initialize a buffer object
    GLuint buffer;
    glGenBuffers( 1, &buffer );
    glBindBuffer( GL_ARRAY_BUFFER, buffer );
    glBufferData( GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW );

    // Load shaders and use the resulting shader program
    GLuint program = InitShader( "vshader21.glsl", "fshader21.glsl" );
    glUseProgram( program );

    // Initialize the vertex position attribute from the vertex shader
    GLuint loc = glGetAttribLocation( program, "vPosition" );
    glEnableVertexAttribArray( loc );
    glVertexAttribPointer( loc, 2, GL_FLOAT, GL_FALSE, 0,
                           BUFFER_OFFSET(0) );

    glClearColor( 1.0, 1.0, 1.0, 1.0 ); // white background
}

//----------------------------------------------------------------------------

void
display( void )
{
    glClear( GL_COLOR_BUFFER_BIT );     // clear the window
    glDrawArrays( GL_POINTS, 0, NumPoints );    // draw the points
    glFlush();
}

//----------------------------------------------------------------------------

void
keyboard( unsigned char key, int x, int y )
{
    switch ( key ) {
    case 033:
        exit( EXIT_SUCCESS );
        break;
    }
}

//----------------------------------------------------------------------------

int
main( int argc, char **argv )
{
    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_RGBA );
    glutInitWindowSize( 512, 512 );

    glutCreateWindow( "Sierpinski Gasket" );

    init();

    glutDisplayFunc( display );
    glutKeyboardFunc( keyboard );

    glutMainLoop();
    return 0;
}

//////////////////////////////////////////////////////////////////////////////
//
//  --- Angel.h ---
//
//   The main header file for all examples from Angel 6th Edition
//
//////////////////////////////////////////////////////////////////////////////

#ifndef __ANGEL_H__
#define __ANGEL_H__

//----------------------------------------------------------------------------
// 
// --- Include system headers ---
//

#include <cmath>
#include <iostream>

//  Define M_PI in the case it's not defined in the math header file
#ifndef M_PI
#  define M_PI  3.14159265358979323846
#endif

//----------------------------------------------------------------------------
//
// --- Include OpenGL header files and helpers ---
//
//   The location of these files vary by operating system.  We've included
//     copies of open-soruce project headers in the "GL" directory local
//     this this "include" directory.
//

#ifdef __APPLE__  // include Mac OS X verions of headers
#  include <OpenGL/OpenGL.h>
#  include <GLUT/glut.h>
#else // non-Mac OS X operating systems
#  include <GL/glew.h>
#  include <GL/freeglut.h>
#  include <GL/freeglut_ext.h>
#endif  // __APPLE__

// Define a helpful macro for handling offsets into buffer objects
#define BUFFER_OFFSET( offset )   ((GLvoid*) (offset))

//----------------------------------------------------------------------------
//
//  --- Include our class libraries and constants ---
//

namespace Angel {

//  Helper function to load vertex and fragment shader files
GLuint InitShader( const char* vertexShaderFile,
           const char* fragmentShaderFile );

//  Defined constant for when numbers are too small to be used in the
//    denominator of a division operation.  This is only used if the
//    DEBUG macro is defined.
const GLfloat  DivideByZeroTolerance = GLfloat(1.0e-07);

//  Degrees-to-radians constant 
const GLfloat  DegreesToRadians = M_PI / 180.0;

}  // namespace Angel

#include "vec.h"
#include "mat.h"
//#include "CheckError.h"

// #define Print(x)  do { std::cerr << #x " = " << (x) << std::endl; } while(0)

//  Globally use our namespace in our example programs.
using namespace Angel;

#endif // __ANGEL_H__

#include "Angel.h"

namespace Angel {

// Create a NULL-terminated string by reading the provided file
static char*
readShaderSource(const char* shaderFile)
{
    FILE* fp = fopen(shaderFile, "r");

    if ( fp == NULL ) { return NULL; }

    fseek(fp, 0L, SEEK_END);
    long size = ftell(fp);

    fseek(fp, 0L, SEEK_SET);
    char* buf = new char[size + 1];
    fread(buf, 1, size, fp);

    buf[size] = '\0';
    fclose(fp);

    return buf;
}


// Create a GLSL program object from vertex and fragment shader files
GLuint
InitShader(const char* vShaderFile, const char* fShaderFile)
{
    struct Shader {
    const char*  filename;
    GLenum       type;
    GLchar*      source;
    }  shaders[2] = {
    { vShaderFile, GL_VERTEX_SHADER, NULL },
    { fShaderFile, GL_FRAGMENT_SHADER, NULL }
    };

    GLuint program = glCreateProgram();

    for ( int i = 0; i < 2; ++i ) {
    Shader& s = shaders[i];
    s.source = readShaderSource( s.filename );
    if ( shaders[i].source == NULL ) {
         std::cerr << "Failed to read " << s.filename << std::endl;
        exit( EXIT_FAILURE );
    }

    GLuint shader = glCreateShader( s.type );
    glShaderSource( shader, 1, (const GLchar**) &s.source, NULL );
    glCompileShader( shader );

    GLint  compiled;
    glGetShaderiv( shader, GL_COMPILE_STATUS, &compiled );
    if ( !compiled ) {
         std::cerr << s.filename << " failed to compile:" << std::endl;
        GLint  logSize;
        glGetShaderiv( shader, GL_INFO_LOG_LENGTH, &logSize );
        char* logMsg = new char[logSize];
        glGetShaderInfoLog( shader, logSize, NULL, logMsg );
         std::cerr << logMsg << std::endl;
        delete [] logMsg;

        exit( EXIT_FAILURE );
    }

    delete [] s.source;

    glAttachShader( program, shader );
    }

    /* link  and error check */
    glLinkProgram(program);

    GLint  linked;
    glGetProgramiv( program, GL_LINK_STATUS, &linked );
    if ( !linked ) {
     std::cerr << "Shader program failed to link" << std::endl;
    GLint  logSize;
    glGetProgramiv( program, GL_INFO_LOG_LENGTH, &logSize);
    char* logMsg = new char[logSize];
    glGetProgramInfoLog( program, logSize, NULL, logMsg );
     std::cerr << logMsg << std::endl;
    delete [] logMsg;

    exit( EXIT_FAILURE );
    }

    /* use program object */
    glUseProgram(program);

    return program;
}

}  // Close namespace Angel block

void
display( void )
{
    glClear( GL_COLOR_BUFFER_BIT );     // clear the window
    glDrawArrays( GL_POINTS, 0, NumPoints );    // draw the points
    glFlush();
}