从一个texture读出rgba数据

    int iBytesPerRow = iWidth * 4;
    unsigned char *baseAddress = malloc(iBytesPerRow * iHeight);
    
    GLuint fboID;
    glGenFramebuffers(1, &fboID);
    glBindFramebuffer(GL_FRAMEBUFFER, fboID);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, inputTexture, 0);
    glPixelStorei(GL_PACK_ALIGNMENT, 1);
    glReadPixels(0, 0, iWidth, iHeight, GL_RGBA, GL_UNSIGNED_BYTE, baseAddress);
    glDeleteFramebuffer(1, &fboID);

将rgba写入一个texture

        GLuint texture;
        glActiveTexture(GL_TEXTURE1);
        glGenTextures(1, &texture);
        glBindTexture(GL_TEXTURE_2D, texture);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width , height, 0, format, GL_UNSIGNED_BYTE, buffer);
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );