How to draw on TPanel

Question

I need to draw on the TPanel, ideally straight, so I don’t have another component on top of it that interferes with the capture of the mousevent event (I want to draw a small “dimensional capture” on it). How can I do it?

Answer 1

For everything to be correct, you should probably write a descendant class. Override the method Paintto draw the dimension pen, and override the methods MouseDown, MouseUpand MouseMoveto add resizing functionality to the control.

I think a better solution than trying to draw TPanelin the application code for several reasons:

• The property Canvasis protected in TPanel, so you do not have access to it from outside the class. You can get around this with a type, but it's a hoax.
• Variability sounds more like a panel function than an application function, so put it in the code for the control panel, and not in the main application code.

Here you can start:

type
  TSizablePanel = class(TPanel)
  private
    FDragOrigin: TPoint;
    FSizeRect: TRect;
  protected
    procedure Paint; override;
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState;
      X, Y: Integer); override;
    procedure MouseMove(Shift: TShiftState; X, Y: Integer); override;
    procedure MouseUp(Button: TMouseButton; Shift: TShiftState;
      X, Y: Integer); override;
  end;

procedure TSizeablePanel.Paint;
begin
  inherited;
  // Draw a sizing grip on the Canvas property
  // There a size-grip glyph in the Marlett font,
  // so try the Canvas.TextOut method in combination
  // with the Canvas.Font property.
end;

procedure TSizeablePanel.MouseDown;
begin
  if (Button = mbLeft) and (Shift = []) 
      and PtInRect(FSizeRect, Point(X, Y)) then begin
    FDragOrigin := Point(X, Y);
    // Need to capture mouse events even if the mouse
    // leaves the control. See also: ReleaseCapture.
    SetCapture(Handle);
  end else inherited;
end;

Answer 2

This is one of many ways that Raize Components can make your life easier. I just go into Delphi, go down to TRzPanel and type:

RzPanel1.Canvas.Rectangle ...

I am sure there are other solutions, but I do not need to look for them with Raize.

(just a satisfied customer for about 10 years ...)

EDIT: , Raize Components, , TRzSizePanel , OnCanResize ( , ).

Answer 3

- TImage . , TCanvas , F1 , . ( , ...)

Answer 4

: http://delphi.about.com/library/weekly/aa110105a.htm

TAdvPanel: http://www.tmssoftware.com/site/advpanel.asp