Hi Part12studios and thank you for this answer !!
i've tried this solution but this wasnt as accurate as i wanted soo i did it like this:
1/ draw a first sprite on the very first touch
2/ compute distance between the last sprite created and current touch position
3/ repeat N times (where N is the result of the division of the distance by a global variable "distanceBetweenPoints")
4/ and inside the repeat loop i'm drawing a point at lastSprite.X and lastSprite.Y + define position by angle where angle = the relative angle to current touch point, and distance = "distanceBetweenPoints"
I hope it's clear :D
with this method the line is very smooth :D
My last problem is to find a way to "pin" each points with the last one created