Does somebody know if it's still possible to make a c_trace go through certain blocks?

This was possible in the past by using passable blocks and setting the IGNORE_PASSABLE flag for c_trace.
However, according to the manual the passable flag for blocks is an "Obsolete flag, for non-mesh levels only".
In fact, passable blocks are not ignored by c_trace anymore, even if IGNORE_PASSABLE is set.

I also tried detail blocks, because these are supposed to be "ignored by the collision detection", but no luck. They aren't ignored by c_trace.

Any other ideas (apart from using entities)?

I think flag2 does that.

Thanks, but IGNORE_FLAG2 only works for entities (tested).

Ah. It's not hard to make blocks in med. And I say this as a programmer.

Check block's flag, and if it's flag for example equals to 5, then traces ignores it.
BTW notice that you need to use SCAN_TEXTURE in trace, to detect block's flag.

Thank you both for your ideas.

As all blocks but the floor in my level need to be ignored by c_trace, I'll export/import the floor as mdl entity. Then I can just use IGNORE_WORLD and trace for the floor entity.

Yeah, there are many workarounds for this situation, all up to you.