“Barycentric Coordinates!” Finally found the term (and the algorythm).
Special Thanks to P.Avery by post the code/question here: http://gamedev.stackexchange.com/questions/62651/finding-pixels-within-uv-coordinates
And yes, if we follow the formula correctly it works pretty well! 
to future Searchs: HOW TO DRAW A FILL TRIANGLE ON MATERIAL
Just remember on pass your triangle Vertices Coordinates as UV positions.
Regards!