Client coordinates in a ScrollBox

[simsee]

In the case of a ScrollBox, is it an expected behavior for event handlers like MouseMove to provide the X,Y coordinates of the mouse pointer without taking into account the position of the scrollbar sliders? In other words, I note that the coordinates refer to the origin of the client's physical window, not the logical one. (under Windows o.s.).

Thanks in advance for the usual help.

[jamie]

yes

[simsee]

Thanks Jamie and sorry for the late response. I thought my question had been ignored.

My post arises from the fact that the MouseMove event handlers do not detect (in my case) the correct coordinates of the mouse pointer when it is over a graphic object in the scrollbox and the sliders are not in the initial position (=0).

Consider the following demo (compilable project attached):

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ExtCtrls;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     ScrollBox1: TScrollBox;
16.     Shape1: TShape;
17.     procedure ScrollBox1MouseMove(Sender: TObject; Shift: TShiftState; X,Y: Integer);
18.     procedure Shape1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
19.   private
20.  
21.   public
22.  
23.   end;
24.  
25. var
26.   Form1: TForm1;
27.  
28. implementation
29.  
30. {$R *.lfm}
31.  
32. { TForm1 }
33.  
34. procedure TForm1.ScrollBox1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
35. begin
36.   Caption:=(X+ScrollBox1.HorzScrollBar.Position).ToString+':'+(Y+ScrollBox1.VertScrollBar.Position).ToString;
37. end;
38.  
39. procedure TForm1.Shape1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
40. begin
41.   if Sender is TShape then
42.     ScrollBox1MouseMove(Sender,Shift,TShape(Sender).Left+X,TShape(Sender).Top+Y);
43. end;
44.  
45. end.

For example, the Y position of the mouse pointer when it is adjacent to the outside of the top side of the square is (wrongly) much smaller than when it is adjacent to the inside (see the blue points in the two screenshots).

Can you help me understand what I did wrong? Thank you.

[jamie]

When you drop a control on a scroll box, the LEFT, TOP of that control already accounts for the offset of the scrollbar.

  Your test code is adding the parent scrollbar position to it.

the X, Y values coming from the mouse always reports Client positions and does not care about the scrollbar, it makes believe there is no such thing. So, what you are getting is what you see in front of you, this also means the scrollbar will block part of the client.

 Maybe I miss understood the situation.

Jamie

[simsee]

Dear Jamie, you certainly understood the situation better than me. Something is still not clear to me. The problem also occurs if TShape objects are created dynamically.

However I solved the problem using a different approach, based upon Mouse.CursorPos, as follows:

Code: Pascal  [Select][+][-]

1. procedure TForm1.Upda]"]>BlockedusePos;
2. begin
3.   with ScreenToClient(Mouse.CursorPos) do
4.     Caption:=(X+ScrollBox1.HorzScrollBar.Position).ToString+':'+(Y+ScrollBox1.VertScrollBar.Position).ToString;
5. end;
6.  
7. procedure TForm1.ScrollBox1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
8. begin
9.   Upda]"]>BlockedusePos;
10. end;
11.  
12. procedure TForm1.Shape1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
13. begin
14.   Upda]"]>BlockedusePos;
15. end;

[jamie]

Ok, hope you are using the TShape from the trunk? That has an excellent addition to it that allows you to specify a polygon enclosure so you can have custom shapes. Also, you can detect if the mouse is clicked within the shape and not the unpainted areas.

[simsee]

Thanks Jamie. I'm using the current release. I didn't know there were these interesting new features in the trunk.

A problem with TShape is that non-rectangular shapes trigger events also when the mouse pointer is not on the surface of the shape, but is inside the rectangle that encloses it. I hope this problem has been resolved.

Going back to my demo, I suspect there is some bug in LCL, but I need to delve deeper.

[simsee]

In the meantime I fixed my first demo program as follows:

Code: Pascal  [Select][+][-]

1. procedure TForm1.ScrollBox1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
2. begin
3.   if Sender is TScrollBox then
4.     begin
5.       X:=X+ScrollBox1.HorzScrollBar.Position;
6.       Y:=Y+ScrollBox1.VertScrollBar.Position;
7.     end;
8.   Caption:=X.ToString+':'+Y.ToString;
9. end;