[Lazarus] Hint as text over TAChart

[Werner Pamler]

The most general way: Use the CurrentExtent of the chart, it is in 
"graph coorinates", though, and you have to convert it to pixels yourself:

uses
   TAChartUtils;

procedure TForm1.Button1Click(Sender: TObject);
var
   ext: TDoubleRect;
begin
   ext := Chart1.CurrentExtent;
   Label1.Caption := Format('Left = %d, Top = %d, Right = %d, Bottom = 
%d', [
     Chart1.XGraphToImage(ext.a.x),   // "a" is the lower left corner
     Chart1.YGraphToImage(ext.b.y),   // "b" is the upper right corner
     Chart1.XGraphToImage(ext.b.x),
     Chart1.YGraphtoImage(ext.a.y)
   ]);
end;

Or you could catch one of the events OnBeforeDrawBackwall or 
OnAfterDrawBackwall which are fired during the painting process and 
contain the rectangle enclosed by the axis lines as a parameter; simply 
store that Rect for later usage.