Printing or PDF with specific scale with OL4

[Bertrand Durand]

Hello, 

I'm using the new OL4 librairy with geoserver 2.11 and I try to make a PDF from my map with a specific scale and it's never right :(

I try to use printing module with geoext but it's only compatible with OL 3 ... 

is there any example with OL 4 ? 

thanks

Bertrand