Draw polygon on Image - delphi

Question

I've been searching this quite a while but couldn't get the answer.
I want to draw a polygon on an image, but I want to do this with by creating points;
With the MouseCursor create this specific points, and with a button draw a line along these points;
I found this:
var
Poly: array of TPoint;
begin
// Allocate dynamic array of TPoint
SetLength(Poly, 6);
// Set array elements
Poly[0] := Point(10, 10);
Poly[1] := Point(30, 5);
Poly[2] := Point(100, 20);
Poly[3] := Point(120, 100);
Poly[4] := Point(50, 120);
Poly[5] := Point(10, 60);
// Pass to drawing routine
Canvas.Polygon(Poly);
// Redim if needed
SetLength(Poly, 7);
Poly[6] := Point(1, 5);
// Pass to drawing routine
Canvas.Polygon(Poly);
end;
This is what I want, but the difference is the Point[1], Point[2], etc is given by the user with a MouseEvent.

Answer 1

You might superimpose a Paintbox over your image and use a code like this
unit Unit3;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls, StdCtrls;
type
TPointArray=array of TPoint;
TForm3 = class(TForm)
Image1: TImage;
PaintBox1: TPaintBox;
Button1: TButton;
procedure PaintBox1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
procedure PaintBox1Paint(Sender: TObject);
procedure Button1Click(Sender: TObject);
private
{ Private-Deklarationen }
FPointArray:TPointArray;
public
{ Public-Deklarationen }
end;
var
Form3: TForm3;
implementation
{$R *.dfm}
procedure TForm3.Button1Click(Sender: TObject);
begin
PaintBox1.Visible := false;
Image1.Canvas.Polygon(FPointArray);
end;
procedure TForm3.PaintBox1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
SetLength(FPointArray,Length(FPointArray)+1);
FPointArray[High(FPointArray)].X := X;
FPointArray[High(FPointArray)].Y := Y;
Paintbox1.Invalidate;
end;
procedure TForm3.PaintBox1Paint(Sender: TObject);
var
i:Integer;
begin
PaintBox1.Canvas.Brush.Style := bsClear; //as suggested by TLama
PaintBox1.Canvas.Polygon(FPointArray);
for I := 0 to High(FPointArray) do
begin
PaintBox1.Canvas.TextOut(FPointArray[i].X-5,FPointArray[i].y-5,IntToStr(i));
end;
end;
end.

Answer 2

Make an array of points managed by your form. Declare a dynamic-array field in your form class:
private
FPoly: array of TPoint;
In your OnClick event, lengthen the array and append a new coordinate to it:
procedure TFruitForm.ImageClick(Sender: TObject);
var
p: TPoint;
begin
p := ...;
SetLength(FPoly, Length(FPoly) + 1);
FPoly[High(FPoly)] := p;
end;
To assign p, see How do I get the coordinates of the mouse when a control is clicked?
Instead of an array, you might also consider using a generic list: TList<TPoint>.