判断一个点是否在矩形内PtInRegion－解决PtInRect不能正确判断不同形式TRent的情况

PtInRegion

API说明：

BOOL PtInRegion(

HRGN hrgn, // handle of region

int X, // x-coordinate of point

int Y // y-coordinate of point

);

Parameters

hrgn

Identifies the region to be examined.

X

Specifies the x-coordinate of the point.

Y

Specifies the y-coordinate of the point.

Return Values

If the specified point is in the region, the return value is nonzero.

Delphi代码：

unit Unit2;

interface

//{$DEFINE LEFTBOTTOM} //注释调此编译开关 PtInRect不能正确判断在该区域的点,PtInRegion能够正确判断

uses

Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

Dialogs;

type

TForm2 = class(TForm)

procedure FormCreate(Sender: TObject);

procedure FormPaint(Sender: TObject);

procedure FormMouseDown(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

procedure FormDestroy(Sender: TObject);

private

{ Private declarations }

p1, p2: TPoint; //p1, p2构成矩形

FRect: TRect;

FRgn: HRGN;

public

{ Public declarations }

end;

var

Form2: TForm2;

implementation

{$R *.dfm}

procedure TForm2.FormCreate(Sender: TObject);

begin

//从p1点向p2点方向画矩形(两个点画矩形有4中可能的情况：即p1为左上，左下，右下，右上坐标点)

{$IFDEF LEFTBOTTOM}

//p1为左下坐标，此时PtInRect能够正确判断在该区域的点

p1.X := 30;

p1.Y := 30;

p2.X := 200;

p2.Y := 110;

{$ELSE}

//p1为右上坐标，此时PtInRect不能正确判断在该区域的点

p1.X := 200;

p1.Y := 110;

p2.X := 30;

p2.Y := 30;

{$ENDIF}

FRect.Left := p1.X;

FRect.Right := p2.x;

FRect.Top := p1.y;

FRect.Bottom:= p2.y;

FRgn := CreateRectRgnIndirect(FRect);

end;

procedure TForm2.FormDestroy(Sender: TObject);

begin

DeleteObject(FRgn);

end;

procedure TForm2.FormMouseDown(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

begin

if PtInRegion(FRgn, X, Y) then {判断鼠标当前点是否在区域内}

ShowMessage('该点在矩形区域内');

end;

procedure TForm2.FormPaint(Sender: TObject);

begin

Canvas.Rectangle(FRect);

end;

end.