Transfer first z or m value to point

[lbartoletti]

Description

This PR is the continuation of the #42812 (comment). It adds a method for adding the Z and the M from a QgsPointSequence. It is equivalent to using the transferFirstZValueToPoint and transferFirstMValueToPoint methods but avoid looping twice.

It is used in the QgsCircle, QgsEllipse, QgsTriangle classes. Three other dedicated PR will complete and add tests on these classes using this method.

Sponsored by: Métropole Européenne de Lille @Jean-Roc

[nyalldawson]

Looks good!

If you wanted to make it super-flexible you could make the new method accept an iterator begin/end argument instead of QgsPointSequence, so that we could potentially call it on other point structures (such as the QgsGeometry vertex iterator) without the added expense of translating those to QgsPointSequence.

Probably not a big factor here, but something to keep in mind for future api additions which are designed to work with larger number of input points.

[lbartoletti]

Gentle ping @nyalldawson 😊

[pblottiere]

Using a generic iterator was indeed a good idea! Code looks good to me.

[pblottiere]

Hi @lbartoletti,

While not strictly being a new feature, this PR is not really a bugfix either. Can we target this for 3.22? And sorry for not having merged sooner...

[nyalldawson]

Looks fantastic to me. I think this is safe to merge for 3.20

[pblottiere]

I think this is safe to merge for 3.20

Nice 🎉!

[lbartoletti]

Thanks @nyalldawson @pblottiere 🙏