Drawing a closed Polygon on an Image
lazarus / 39-Graphics

----------------------------------------------------------------------
Boleeman · 2023-11-04 09:00

Hi All.

Been playing around with drawing a closed polygon on an Image1

Just wanted to find out how:

1.   To make the Image1 background  initially WHITE and then have the
background remain white while making a blue filled polygon.
     (The image turns black after it is initially clicked)

2.   Also, how would you use the left mouse button to start a new
polygon, while still leaving the previous one still there.

I apologize for asking some probably simple questions, but I was Kinda
going round in circles.

----------------------------------------------------------------------
paweld · 2023-11-04 10:18

1. instead of:Code: [Select]  Image1.Canvas.Brush.Style :=
bsClear;setCode: [Select]  Image1.Canvas.Brush.Style := bsSolid;
  Image1.Canvas.Brush.Color := clWhite;
  Image1.Canvas.FillRect(Image1.ClientRect);   
2. revised project attached   
 
And anyway, for such operations the best is PaintBox

----------------------------------------------------------------------
Boleeman · 2023-11-04 11:23

Thanks for the example Paweld

That is exactly what I was looking for.

Initial click is left, then followed by right clicks.

I saw a few other threads that mentioned using a Paintbox instead of
Image.
Now I see why.

I decided to look more into polygons after failing with that Rose
Curve conversion with generics.
I will look over both codes to learn a few of your techniques.

With this example I liked the way you prefixed the shape vertices with
FPoly[j].X - 10, FPoly[j].y - 10

Thank you paweld once again for you great help.

----------------------------------------------------------------------
paweld · 2023-11-04 11:59

I just saw that there is still a piece of unnecessary code - creating
a bitmap in OnMouseDown - the final procedure should look like
thisCode: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.PaintBox1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);var  p: TPoint;  polyidx, ptidx:
Integer;begin  polyidx := Length(FPoly) - 1;  if polyidx >= 0 then   
ptidx := Length(FPoly[polyidx]) - 1  else    ptidx := -1;  if (Button
= mbLeft) or (polyidx < 0) then  //if mouse button left or no
polygons  begin    //create new polygon    Inc(polyidx);    ptidx :=
-1;    SetLength(FPoly, polyidx + 1);    SetLength(FPolyColor, polyidx
+ 1);    FPolyColor[polyidx] := RGBToColor(Random(255), Random(255),
Random(255));  //and set random pen color  end;  Inc(ptidx); 
SetLength(FPoly[polyidx], ptidx + 1);   p := Mouse.CursorPos; 
FPoly[polyidx][ptidx] := PaintBox1.ScreenToClient(p);  // or do this 
//FPoly[polyidx][ptidx].X := X;  //FPoly[polyidx][ptidx].Y := Y; 
PaintBox1.Invalidate;end;