https://www.khronos.org/registry/OpenGL-Refpages/es3.0/html/glRenderbufferStorage.xhtml
https://www.khronos.org/registry/OpenGL-Refpages/es3.0/html/glRenderbufferStorageMultisample.xhtml
glRenderbufferStorage — establish data storage, format and dimensions of a renderbuffer object's image
有点像descriptor
bind前后用 sample
//渲染缓冲区作为颜色缓冲区
glGenRenderbuffers（1，& colorBuffer）;
glBindRenderbuffer（GL_RENDERBUFFER，colorBuffer）;
glRenderbufferStorage（GL_RENDERBUFFER，GL_RGBA，width，height）;
glBindRenderbuffer（GL_RENDERBUFFER，0）;
//将渲染缓冲区作为颜色缓冲区附加到fbo
glFramebufferRenderbuffer（GL_FRAMEBUFFER，GL_COLOR_ATTACHMENT0，GL_RENDERBUFFER，colorBuffer）;
有了扩展就可以用glRenderbufferStorageMultisample 作为ogles上msaa stay in tile 的解决方案（memoryless）
kGL_EXT_multisampled_render_to_texture
kGL_IMG_multisampled_render_to_texture
kGL_APPLE_framebuffer_multisample（apple现在用metal
kGL_NV_framebuffer_multisample kGL_NV_framebuffer_blit