再學 GDI+[12]: 准備工作 - 矩形命中

　本例效果圖:

　　代碼文件:unit Unit1;
interface
uses
　Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
　Dialogs;
type
　TForm1 = class(TForm)
　　procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
　　　Shift: TShiftState; X, Y: Integer);
　　procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
　　procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
　　　Shift: TShiftState; X, Y: Integer);
　　procedure FormPaint(Sender: TObject);
　end;
var
　Form1: TForm1;
implementation
{$R *.dfm}
uses GDIPOBJ, GDIPAPI;
var
　f: Boolean;
　x1,y1,x2,y2: Integer;
　RectArr: array of TRect;
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
　Shift: TShiftState; X, Y: Integer);
begin
　f := True;
　x1 := X;
　y1 := Y;
　x2 := X;
　y2 := Y;
end;
procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
　Y: Integer);
var
　i: Integer;
begin
　if f then
　begin
　　Canvas.DrawFocusRect(Rect(x1,y1,x2,y2));
　　x2 := X;
　　y2 := Y;
　　Canvas.DrawFocusRect(Rect(x1,y1,x2,y2));
　end else begin
　　Text := '';
　　for i := Low(RectArr) to High(RectArr) do
　　　if PtInRect(RectArr[i], Point(X,Y)) then
　　　　Text := Format('在第 %d 個矩形中', [i+1]);
　end;
end;
procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
　Shift: TShiftState; X, Y: Integer);
begin
　if not f then Exit;
　SetLength(RectArr, Length(RectArr)+1);
　RectArr[High(RectArr)] := Rect(x1,y1,x2,y2);
　f := False;
　Repaint;
end;
procedure TForm1.FormPaint(Sender: TObject);
var
　g: TGPGraphics;
　p: TGPPen;
　i: Integer;
begin
　g := TGPGraphics.Create(Canvas.Handle);
　p := TGPPen.Create(aclRed, 1);
　g.Clear(aclWhite);
　for i := Low(RectArr) to High(RectArr) do
　　g.DrawRectangle(p, MakeRect(RectArr[i]));
　g.Free;
　p.Free;
end;
end.窗體文件:object Form1: TForm1
　Left = 0
　Top = 0
　Caption = 'Form1'
　ClIEntHeight = 179
　ClIEntWidth = 277
　Color = clBtnFace
　Font.Charset = DEFAULT_CHARSET
　Font.Color = clWindowText
　Font.Height = -11
　Font.Name = 'Tahoma'
　Font.Style = []
　OldCreateOrder = False
　Position = poDesktopCenter
　OnMouseDown = FormMouseDown
　OnMouseMove = FormMouseMove
　OnMouseUp = FormMouseUp
　OnPaint = FormPaint
　PixelsPerInch = 96
　TextHeight = 13
end