This isn't supposed to be something very fast and impressive and especially this is my first triangle filler. Also it has many problems that I will try to fix later.
My method: - find slope for every edge (m1, m2, m3) - find y-intersect for every edge (b1, b2, b3) - find out if one or another edge is on the current row (yi1, yi2, yi3) - find x-position of the point on edges that intersect with the current row - go to closest edge point - put pen down - go to last edge point - put pen up - go to next line - repeat for whole triangle
