Determine the right cell in TDrawgrid with mousecursor
lazarus / 31-LCL

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mangakissa · 2014-10-30 11:07

In this topic I got showhint on every cell. But there's something
strange. My TDrawgrid is indexed to 500 cels (20 cols * 25 rows). To
determine the position of the mousecursor I had to use OnMouseMove and
saved X and Y in a variabele. This peace of code will tel me on which
cell my mousecursor is focused.
Code: [Select]procedure TFrmPuzzelstukjes.PuzzelGridMouseMove(Sender:
TObject;
  Shift: TShiftState; X, Y: Integer);
begin
  fXas := X;
  fYas := Y;
end;

procedure TFrmPuzzelstukjes.DoShowHint(Sender: TObject; HintInfo:
PHintInfo);
var ax,ay     : longint;
    col, row  : integer;
    celnumber : integer;
begin
  TDrawGrid(Sender).MouseToCell(HintInfo^.CursorPos.X,HintInfo^.Cursor
Pos.Y,ax,ay);
  col := fXas div 20;
  row := fYas div 20;
  celnumber := (row * 20) + col + 1;
  HintInfo^.HintStr:= format('col (%d): %d, row (%d): %d, celnumber:
%d',[fXas,col,fYas,row,celnumber]);
end;
But when my mousecursor is located on cell 20, it's telling me cell 25
is focused. A small calculation: 485 (X) div 20 (number of cols in a
row) = 24.

OnMouseMove is giving te right X position, because TDrawgrid.width is
504.

How can I calculate the right index of the cell where the mousecursor
is focused?

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Blaazen · 2014-10-30 11:21

IMO you are doing it wrong. You should calculate

CellColumn = MouseX / WidthOfColumn.

And it will work, of course, only if all columns has the same width
and grid is not scrolled out.

And the same is for rows.

CellRow = MouseY / HeightOfRows.

EDIT: I realized now that there's property GridLineWidth (default 1)
which you should take into account too.

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wp · 2014-10-30 11:45

@mangakissa: Did you look at the source in grids.pas? Always a good
idea... You'll see that TCustomGrid has a method for determining the
rectangle enclosing a cell:

Code: [Select]    function CellRect(ACol, ARow: Integer): TRect;

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mangakissa · 2014-10-30 15:20

@wp

AFAIK CellRect is nice if you know the cell's col and row. You don't
know it if you are using a mouse on it.

@blaazen
Thanks.  I knew I did something wrong.
Just found out it should be this
Code: [Select]col := fXas div 25;
row := fYas div 25;
Because the cell is 25 * 25 pixels.
But your solution is much better and dynamic.

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wp · 2014-10-30 15:52

Quote if you know the cell's col and row.But you know that from
MouseToCell which you are calling ?!

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User137 · 2014-10-30 17:11

Col, Row is in those ax, ay you ignored?

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mangakissa · 2014-10-31 07:23

I read the ax and yx and those gave me the range of the cell, not the
col and row. But I solved it (thanks to Bart) with this:
Code: [Select]TCustomGrid(Sender).MouseToCell(HintInfo^.CursorPos.X,Hi
ntInfo^.CursorPos.Y,Col, Row);
It seems property MouseToCell from TDrawgrid has a different approach
than TCustomgrid.

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wp · 2014-10-31 08:28

QuoteIt seems property MouseToCell from TDrawgrid has a different
approach than TCustomgrid.Nonsense - look at the source code:
TDrawGrid inherits from TCustomDrawGrid which in turn inherits from
TCustomGrid. MouseToCell is implemented only in TCustomGrid,
therefore, TDrawGrid uses the same MouseToCell code as TCustomGrid.

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mangakissa · 2014-10-31 12:19

You're right. My apologies. I thought I saw different values but now I
see the same (put a memo on screen to see what happens).

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wp · 2014-10-31 12:43

No need to apologize - sometimes we all don't see the obvious.