You can draw progressively a line with dots using BGRABitmap, more precisely:
procedure DrawLineAntialias(x1, y1, x2, y2: integer; c1, c2: TBGRAPixel; dashLen: integer; DrawLastPixel: boolean; var DashPos: integer);
First initialize DashPos variable to zero and pass it as a parameter. Its value will change in order to continue the line properly. If you want a simple dash, set c1 to the color of the dashes and c2 to BGRAPixelTransparent.