Creating Multisample Texture Correctly

Question

For standard OpenGL textures, the filtering state is part of the texture, and must be defined when the texture is created. This leads to code like:

glGenTextures(1,&_texture_id);
glBindTexture(GL_TEXTURE_2D,_texture_id);
glTexParameterf(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
glTexImage2D(...);

This works perfectly. I am trying to make a multisampled texture (for use in a FBO). The code is very similar:

glGenTextures(1,&_texture_id);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE,_texture_id);
glTexParameterf(GL_TEXTURE_2D_MULTISAMPLE,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D_MULTISAMPLE,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
glTexImage2DMultisample(...);

I am using a debug context, and with this code the first glTexParameterf(...) call causes:

GL_INVALID_ENUM error generated. multisample texture targets doesn't support sampler state

I don't know what this is supposed to mean. Notice that multisampled textures only support nearest filtering. I am specifying this. I noticed that for some of the calls (in particular glTexParameterf(...)), the GL_TEXTURE_2D_MULTISAMPLE is not a listed input in the documentation (which would indeed explain the invalid enum error if they're actually invalid, not just forgotten). However, if it is not accepted, then how am I supposed to set nearest filtering?

Answer 1

You do not need to set nearest filtering because multisample textures are not filtered at all. The specification (section 8.10) does list GL_TEXTURE_2D_MULTISAMPLE as a valid target for glTexParameteri (which you should use instead of glTexParameterf for integer parameters), but lists among possible errors:

An INVALID_ENUM error is generated if target is either TEXTURE_2D_MULTISAMPLE or TEXTURE_2D_MULTISAMPLE_ARRAY, and pname is any sampler state from table 23.18.