c# - GraphicsPath.AddPolygon not rendering properly -

basically have form , trying "dim" areas of draw focus part of form. i'm using form no border , 50% opacity, aligned actual form. area trying mask dark gray area, roughly, pictured:

to "u"-shaped form, i'm using graphicspath addpolygon, calculating points of each vertex:

var p = new graphicspath(); var origin = new point(top, left); var maxextentpt = new point(origin.x + width, origin.y + height); point[] points = {     origin,      new point(origin.x + leftpanel.width, origin.y),     new point(origin.x + leftpanel.width, maxextentpt.y - bottompanel.height),     new point(maxextentpt.x - rightpanel.width, maxextentpt.y- bottompanel.height),     new point(maxextentpt.x - rightpanel.width, origin.y),     new point(maxextentpt.x, origin.y),     maxextentpt,     new point(origin.x, maxextentpt.y),     origin }; p.addpolygon(points); overlayform.region = new region(p); overlayform.location = pointtoscreen(point.empty); 

the 3 panels in code masking, using dimensions calculate points. instead of getting expected result, mask looks this, size changing resize main form (i recalculate region on move , resize):

is there limitation of graphicspath.addpolygon i'm not aware of? double-checked (quadruple-checked, really) results of calculations, including taking coordinates each point , plugging them ipe see if shape correct... was. not in program!

edit: here values of each point, when hit breakpoint @ p.addpolygon(points); i'm starting in upper left-hand corner , going around clockwise:

looks points wrong after all.

everything ought in coordinates of clientrectangle, so

origin should not new point(top, left) location of form. should point.empty or (0,0). or use leftpanel.location.

and

maxextentpt = new point(origin.x + width, origin.y + height); 

should read:

var maxextentpt = new point(origin.x + clientsize.width, origin.y + clientsize.height); 

(the difference size of border+title..)

let me know if works better!