用delphi怎么画透明的圆

Question

我用Image2.Canvas.Ellipse(Circle.Left,Circle.Top,Circle.Right,Circle.Bottom);
画的圆是实心的，如何画空心圆？

Answer 1

那是因为image本身的问题，只要在上面画，就会自动有背景颜色，你可以在其他组件上画，比如form或者panel

Answer 2

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls;type
  TForm1 = class(TForm)
    procedure FormPaint(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.FormPaint(Sender: TObject);
begin
  canvas.Pen.Color:=clGreen;
  canvas.Ellipse(100,100,300,300);
end;end.

Answer 3

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls;type
  TForm1 = class(TForm)
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
  private
     fselecting:boolean;
     fbeginpt,fendpt:tpoint;
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  fselecting:=true;
  fbeginpt:=Form1.ScreenToClient(mouse.CursorPos);
end;procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  fselecting:=false;
  fendpt:=Form1.ScreenToClient(mouse.CursorPos);
  Self.Repaint;
end;procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  fendpt:=Form1.ScreenToClient(mouse.CursorPos);
  if fselecting then
  begin
    Canvas.FillRect(Canvas.ClipRect);
    canvas.Ellipse(rect(fbeginpt,fendpt));
    canvas.Pen.Color:=clred;
    Canvas.Pen.Width:=1;
  end;
end;end.

Answer 4

这个就可以，画之前先设置
Canvas.Brush.Style := bsClear;

Answer 5

另类思路：放个圆形、透明的Tshape