获取多边形面积的函数 - 回复 "dacsd" 的问题

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

{获取多边形面积的函数}
function GetPolygonArea(const pt: PPoint; const Count: Integer): Double;
function LineSqr(const pt1,pt2: TPoint): Double;
begin
Result := (pt2.X - pt1.X) * (pt1.Y + pt2.Y) / 2;
end;
type
ArrPt = array of TPoint;
var
i: Integer;
begin
Result := 0;
for i := 0 to Count - 2 do
Result := Result + LineSqr(ArrPt(pt)[i], ArrPt(pt)[i+1]);
Result := Result + LineSqr(ArrPt(pt)[Count-1], ArrPt(pt)[0]);
end;

{测试1: 把窗体矩形当个多边形测试一下, 使用静态数组}
procedure TForm1.Button1Click(Sender: TObject);
var
pts: array[0..3]of TPoint;
Area1: Double;
Area2: Integer;
begin
pts[0] := ClientRect.TopLeft;
pts[1] := Point(0, ClientHeight);
pts[2] := ClientRect.BottomRight;
pts[3] := Point(ClientWidth, 0);

{用上面的函数获取面积}
Area1 := GetPolygonArea(@pts, Length(pts));
{用 宽*高 获取面积}
Area2 := ClientWidth * ClientHeight;
{对比显示两个结果}
Text := Format('%f, %d', [Area1, Area2]); {没有问题}
end;

{测试2: 把窗体用对角线分隔的三角形当个多边形测试一下, 使用动态数组}
procedure TForm1.Button2Click(Sender: TObject);
var
pts: array of TPoint;
Area1: Double;
Area2: Integer;
begin
SetLength(pts, 3);
pts[0] := ClientRect.TopLeft;
pts[1] := Point(0, ClientHeight);
pts[2] := ClientRect.BottomRight;

{用上面的函数获取面积}
Area1 := GetPolygonArea(@pts[0], Length(pts));
{用 宽*高/2 获取面积}
Area2 := ClientWidth * ClientHeight div 2;
{对比显示两个结果}
Text := Format('%f, %d', [Area1, Area2]); {没有问题}
end;

end.

object Form1: TForm1
Left = 0
Top = 0
Caption = 'Form1'
ClientHeight = 206
ClientWidth = 339
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'Tahoma'
Font.Style = []
OldCreateOrder = False
PixelsPerInch = 96
TextHeight = 13
object Button1: TButton
Left = 136
Top = 72
Width = 75
Height = 25
Caption = 'Button1'
TabOrder = 0
OnClick = Button1Click
end
object Button2: TButton
Left = 136
Top = 112
Width = 75
Height = 25
Caption = 'Button2'
TabOrder = 1
OnClick = Button2Click
end
end