opengl - 如何修复以下 gcc 警告？

Question

我已经开始学习 OpenGL 并设法使用顶点缓冲区对象创建一个旋转立方体。但是，当我编译代码时，gcc 会发出以下警告:

|| sdlogl.c: In function ‘initGL’:
sdlogl.c|48| warning: implicit declaration of function ‘glGenBuffers’
sdlogl.c|50| warning: implicit declaration of function ‘glBindBuffer’
sdlogl.c|51| warning: implicit declaration of function ‘glBufferData’

我应该如何解决这些警告？

这是我的代码:

#include <SDL/SDL.h>
#include <SDL/SDL_opengl.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glext.h>

SDL_Surface *surface;
float rquad=0.0f;
GLuint vertexBuffer,colorBuffer;

float vert[]={
     1, 1, 1,   1, 1,-1,  -1, 1,-1,  -1, 1, 1,
     1,-1, 1,   1,-1,-1,  -1,-1,-1,  -1,-1, 1,
     1, 1, 1,   1,-1, 1,   1,-1,-1,   1, 1,-1,
    -1, 1, 1,  -1,-1, 1,  -1,-1,-1,  -1, 1,-1,
     1, 1, 1,  -1, 1, 1,  -1,-1, 1,   1,-1, 1,
     1, 1,-1,  -1, 1,-1,  -1,-1,-1,   1,-1,-1
};
float colors[]={
    1,0,0,  1,0,0,  1,0,0,  1,0,0,
    0,1,0,  0,1,0,  0,1,0,  0,1,0,
    0,0,1,  0,0,1,  0,0,1,  0,0,1,
    1,1,0,  1,1,0,  1,1,0,  1,1,0, 
    1,0,1,  1,0,1,  1,0,1,  1,0,1, 
    0,1,1,  0,1,1,  0,1,1,  0,1,1
};

Uint32 timerfunc(Uint32 interval,void* param){
    rquad+=0.8f;
    return interval;
}

void initGL(){

    glViewport(0,0,640,480);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45,640.0/480.0,0.1,100);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glShadeModel(GL_SMOOTH);
    glClearColor(0,0,0,0);
    glClearDepth(1);
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);

    glGenBuffers(1,&vertexBuffer);
    glGenBuffers(1,&colorBuffer);
    glBindBuffer(GL_ARRAY_BUFFER,vertexBuffer);
    glBufferData(GL_ARRAY_BUFFER,72*sizeof(float),vert,
            GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER,colorBuffer);
    glBufferData(GL_ARRAY_BUFFER,72*sizeof(float),colors,
            GL_STATIC_DRAW);
}

void drawGLScene(){
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    glTranslatef(0,0,-6);
    glRotatef(rquad,1,1,0.5);

    glBindBuffer(GL_ARRAY_BUFFER,vertexBuffer);
    glVertexPointer(3,GL_FLOAT,0,0);
    glBindBuffer(GL_ARRAY_BUFFER,colorBuffer);
    glColorPointer(3,GL_FLOAT,0,0);

    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_COLOR_ARRAY);

    glDrawArrays(GL_QUADS,0,24);

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_COLOR_ARRAY);

    glBindBuffer(GL_ARRAY_BUFFER,0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,0);

    SDL_GL_SwapBuffers();
}

int main(int argc, char** argv){
    int videoFlags=0;
    videoFlags|=SDL_OPENGL;
    videoFlags|=SDL_GL_DOUBLEBUFFER;
    videoFlags|=SDL_HWPALETTE;
    videoFlags|=SDL_HWSURFACE;
    videoFlags|=SDL_HWACCEL;

    int done=0;
    SDL_Event event;
    const SDL_VideoInfo* videoInfo;

    SDL_Init(SDL_INIT_VIDEO|SDL_INIT_TIMER);
    videoInfo=SDL_GetVideoInfo();
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER,1);

    SDL_WM_SetCaption("Hello OpenGL!",NULL);
    surface=SDL_SetVideoMode(640,480,32,videoFlags);

    initGL();
    SDL_AddTimer(10,timerfunc,NULL);
    while(!done){
        while(SDL_PollEvent(&event)){
            if(event.type==SDL_QUIT){
                done=1;
            }
        }
        drawGLScene();
    }
    SDL_Quit();
    return 0;
}

此外，我使用以下命令编译代码:gcc sdlogl.c -g -Wall -lSDL -lGL -lGLU

Answer 1

您收到的这些警告告诉您，上述函数的原型(prototype)尚未正确声明，并且编译器假定默认的 C 函数签名 int ()。

包含 glext.h 不会为您提供声明(出于各种原因)，但会为您提供适当的 typedef 来自行引入这些标识符。但随着时间的推移，它会变得乏味。这就是实现包装器库的原因。我推荐 GLEW 或 GLEE。使用 GLEE，整个事情归结为包含 GL/glee.h 而不是 GL/gl.h。