Question: Why do the drawn points by pointplot look unclear?

The graph we draw in the graph theory package appear to be vectorial. So the export pdf is also clear. 

with(GraphTheory):
DrawGraph(PathGraph(2), stylesheet=[vertexborder=false,
vertexpadding=5,edgecolor = blue,vertexcolor=black,edgethickness=2],size=[250,250])

draw1.pdf

We know that DrawGraph only offers straight forms for drawn edges.  Sometimes we need to draw graphs with curves.  But when I try to use maple, I find that the vertices (by pointplot) are blurred after zooming in (or even without zooming out).

with(plottools):    
with(plots):
Bezier:=proc(x0,y0,x1,y1,x2,y2,x3,y3)
local f,g,c,l1,l2,l3,p0,p1,p2,p3;
f:=t->x0*(1-t)^3+3*x1*t*(1-t)^2+3*x2*t^2*(1-t)+x3*t^3:
g:=t->y0*(1-t)^3+3*y1*t*(1-t)^2+3*y2*t^2*(1-t)+y3*t^3:
c:=plot([f(t),g(t),t=0..1],thickness=2,scaling=constrained, color=blue,axes=none):
p0:=pointplot([x0,y0],symbol= solidcircle,symbolsize = 50,color=black):
p1:=pointplot([x3,y3],symbol= solidcircle,symbolsize = 50,color=black):
display(c,p0,p1,size=[300,300]);
end:

x0:=0:   y0:=0:
x1:=-0.2:  y1:=0.2:
x2:=0.5:  y2:=0.2:
x3:=0.3:  y3:=0:
p:=Bezier(x0,y0,x1,y1,x2,y2,x3,y3)

 draw2.pdf 

How to make these vertices vectorially drawn (like DrawGraph)？