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TGraphObject.HitTesting.md

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TGraphObject.HitTesting.md

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Graph Object Hit-Testing

The hit-test result of a graph object is a mask of 32-bit values. Presence of each value in the result, determines which part of the graph object is at the point of hit-testing.

Value Meaning Scope
GHT_NOWHERE The point is not on the object. TGraphObject
GHT_TRANSPARENT The point is on the object, but the object is not selectable. TGraphObject
GHT_LEFT The point is on the left side of the object. TGraphNode
GHT_TOP The point is on the top side of the object. TGraphNode
GHT_RIGHT The point is on the right side of the object. TGraphNode
GHT_BOTTOM The point is on the bottom side of the object. TGraphNode
GHT_TOPLEFT The point is on the top-left corner of the object. TGraphNode
GHT_TOPRIGHT The point is on the top-right corner of the object. TGraphNode
GHT_BOTTOMLEFT The point is on the bottom-left corner of the object. TGraphNode
GHT_BOTTOMRIGHT The point is on the bottom-right corner of the object. TGraphNode
GHT_CLIENT The point is on the body of the object. TGraphObject
GHT_CAPTION The point is on the caption of the object. TGraphObject
GHT_POINT The point is on one of the control points of the object. The high-order word holds the point's index. TGraphLink
GHT_LINE The point is on one of the line segments of the object. The high-order word holds the line's index. TGraphLink

For example, the following function returns the index of a breakpoint/endpoint of a given link, if the mouse pointer is over such point.

function IndexOfPointUnderMouseCursor(Link: TGraphLink): Integer;
var
  HT: DWord;
begin 
  HT := Link.HitTest(Link.Owner.CursorPos);
  if (HT and GHT_POINT) <> 0 then
    Result := HiWord(HT)
  else
    Result := -1;
end;