With[{coord = {{2, 0}, {-1, 2}, {0, -2}},
gridset =
Join[{#, GrayLevel[.6]} & /@ Range[-3, 3], {#, GrayLevel[.9]} & /@
Complement[Range[-3, 3, 1/10], Range[-3, 3]]]},
GraphicsBox[{
TagBox[
StyleBox[PolygonBox[coord],
Directive[FaceForm[],
EdgeForm[{Thickness[0], Hue[1, 1, 0.7], Opacity[1]}]]],
"DynamicName", BoxID -> "VertexID$1"],
StyleBox[PointBox[DynamicLocation["VertexID$1", Automatic, #]],
Blue, PointSize[.01]] & /@ {Left, Right, Top, Bottom},