opengl - 使用 VBO 的纹理绑定(bind)无法正常工作

Question

我的程序的目的是显示 2 个具有 2 个不同纹理的四边形。问题是加载的最旧的纹理设置在两个四边形上(仅 texQuadB)。我尝试用 texQuadA 和 texQuadB 替换 buf[3] 的两次调用，但它不起作用。我找不到将纹理与特定 VBO 绑定(bind)的正确方法。

#define OFFSET_BUFFER(bytes) ((GLfloat *)NULL + bytes)

GLfloat verticesQuadA[12] =
{
    -1.0f, 0.0f, 1.0f,
    -1.0f, 1.0f, 1.0f,
    0.0f, 1.0f, 1.0f,
    0.0f, 0.0f, 1.0f,
};

GLfloat verticesQuadB[12] =
{
    0.0f, 0.0f, 1.0f,
    0.0f, 1.0f, 1.0f,
    1.0f, 1.0f, 1.0f,
    1.0f, 0.0f, 1.0f,
};

GLfloat colors[12] =
{
    1.0f, 0.0f, 0.0f,
    0.0f, 1.0f, 0.0f,
    0.0f, 0.0f, 1.0f,
    1.0f, 0.0f, 1.0f,
};

GLfloat texture[8] =
{
    0.0f, 0.0f,
    1.0f, 0.0f,
    1.0f, 1.0f,
    0.0f, 1.0f
};

int main(int argc, char *argv[])
{
    SDL_Init(SDL_INIT_VIDEO);
    SDL_WM_SetCaption("Texture Mapping",NULL);
    SDL_SetVideoMode(500, 500, 32, SDL_OPENGL);

    bool continuer = true;
    SDL_Event event;
    GLuint  buf[4];
    GLuint texQuadA, texQuadB;

    glClearDepth(1.0f);
    glClearColor(0.1f, 0.1f, 0.1f, 0.1f);
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(70.0f, (float)500.0f / (float)500.0f, 1.0f, 3000.0f);
    glewInit();

    texQuadA = loadTexture("caisse.jpg");
    texQuadB = loadTexture("metal.jpg");

    //glBindTexture(GL_TEXTURE_2D, texQuadA);
    //glBindTexture(GL_TEXTURE_2D, texQuadB);

    glGenBuffers(4, buf);

    glBindBuffer(GL_ARRAY_BUFFER, buf[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(verticesQuadA), verticesQuadA, GL_STATIC_DRAW);

    glBindBuffer(GL_ARRAY_BUFFER, buf[1]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(verticesQuadB), verticesQuadB, GL_STATIC_DRAW);

    glBindBuffer(GL_ARRAY_BUFFER, buf[2]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(colors), colors, GL_STATIC_DRAW);

    glBindBuffer(GL_ARRAY_BUFFER, buf[3]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(texture), texture, GL_STATIC_DRAW);

    while (continuer)
    {
        SDL_WaitEvent(&event);
        switch(event.type)
        {
            case SDL_QUIT:
                continuer = false;
        }

        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glEnable(GL_TEXTURE_2D);

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        gluLookAt(0.0f, 0.0f, 3.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);

        //Draw Quad A ---------------------------------------

        glBindBuffer(GL_ARRAY_BUFFER, buf[0]);
        glVertexPointer(3, GL_FLOAT, 0, OFFSET_BUFFER(0));

        glBindBuffer(GL_ARRAY_BUFFER, buf[2]);
        glColorPointer(3, GL_FLOAT, 0, OFFSET_BUFFER(0));

        glBindBuffer(GL_ARRAY_BUFFER, buf[3]);
        glTexCoordPointer(2, GL_FLOAT, 0, OFFSET_BUFFER(0));

        glEnableClientState(GL_VERTEX_ARRAY);
        glEnableClientState(GL_COLOR_ARRAY);
        glEnableClientState(GL_TEXTURE_COORD_ARRAY);

        glDrawArrays(GL_QUADS, 0, 4);

        glDisableClientState(GL_TEXTURE_COORD_ARRAY);   
        glDisableClientState(GL_COLOR_ARRAY);
        glDisableClientState(GL_VERTEX_ARRAY);

        //Draw Quad B ---------------------------------------

        glBindBuffer(GL_ARRAY_BUFFER, buf[1]);
        glVertexPointer(3, GL_FLOAT, 0, OFFSET_BUFFER(0));

        glBindBuffer(GL_ARRAY_BUFFER, buf[2]);
        glColorPointer(3, GL_FLOAT, 0, OFFSET_BUFFER(0));

        glBindBuffer(GL_ARRAY_BUFFER, buf[3]);
        glTexCoordPointer(2, GL_FLOAT, 0, OFFSET_BUFFER(0));

        glEnableClientState(GL_VERTEX_ARRAY);
        glEnableClientState(GL_COLOR_ARRAY);
        glEnableClientState(GL_TEXTURE_COORD_ARRAY);

        glDrawArrays(GL_QUADS, 0, 4);

        glDisableClientState(GL_TEXTURE_COORD_ARRAY);   
        glDisableClientState(GL_COLOR_ARRAY);
        glDisableClientState(GL_VERTEX_ARRAY);

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

        glFlush();
        SDL_GL_SwapBuffers();
    }
    glDeleteBuffers(3, buf);
    glDisable(GL_TEXTURE_2D);
    SDL_Quit();

    return 0;
}

Answer 1

OpenGL 是一个状态机。绑定(bind)纹理是设置该状态的一部分。启用纹理后，OpenGL 将在绘制几何体时使用当前纹理状态(您绑定(bind)的最后一个纹理)。在绘制 Quad A 之前，请绑定(bind) texQuadA。在绘制Quad B之前，绑定(bind)texQuadB:

glBindTexture(GL_TEXTURE_2D, texQuadA);
// Draw Quad A

glBindTexture(GL_TEXTURE_2D, texQuadB);
// Draw Quad B

在这种情况下，VBO 是不相关的。