Bug 35448

transset on the xclock window works fine with compiz (and presumably any
other composite manager supporting the standard transparency mechanisms).

What more do you want in xclock than that?

I am not a compiz fan because I am using fvwm. 
And it seems compiz a script-based application, so it may be a little bit resource-consuming.

I tried to use xcompmgr & transset to make the transparency for xclock, but I found the transparency is not the same thing as I expected.

transset's transparency is a full transparency, but what I am expecting is only to remove the background color for xclock with a '-shape' option like xlogo & xeyes do and the clock face still remains the same.

Oh, then use oclock, the analog clock program from X.Org with shaped window
support.

I don't think you really give a solution.
oclock is not the same as xclock.

Maybe you think it is no important or just meaningless, but anyway you have the right to close it.

Then I don't understand what you're asking for.

In any case, we'll consider patches submitted (though adding features like
this to xclock will make it not be small anymore, and bloat it like the
other clock apps you don't like), but since xclock doesn't have any active
maintainers or developers, I don't think anyone here will go off and write it.

It should be true that xclock has no active maintainers, because it is too long time no change.
I think the feature does't have ability to bloat xclock even a bit. it is tiny enough that many other X small apps have it also. The implementation may just be a task of several minutes for a proficient X apps developer. But I doubt it is true that be hard to find one developer who is spare and also has interests.