GDI+ 閉合樣條曲線：DrawClosedCurve 自動閉合與張力控制

DrawClosedCurve 類似 DrawCurve，但會自動將首尾點連接形成閉合曲線。同樣支援張力參數控制彎曲度，適合繪製有機形狀、氣泡、葉片等閉合輪廓。

參數說明

g.DrawClosedCurve(p, PGPPoint(PtArr), Length(PtArr), tension);

• PtArr：控制點陣列 (至少 3 點)
• tension：張力參數 (預設 0.5，0 為直線多邊形)

程式碼實作

點擊新增點，軌跡條調整張力 (-2.5 ~ 3.5)，按鈕清空：

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    TrackBar1: TTrackBar;
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormPaint(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure TrackBar1Change(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
uses GDIPOBJ, GDIPAPI;

var
  PtArr: array of TGPPoint;
  i: Integer = 0;
  tension: Single;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Button1.Caption := '擦除';
  TrackBar1.ShowSelRange := False;
  TrackBar1.Min := -25;
  TrackBar1.Max := 35;
  TrackBar1.Position := 5;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  Inc(i);
  SetLength(PtArr, i);
  PtArr[i - 1].X := X;
  PtArr[i - 1].Y := Y;
  Text := IntToStr(i);
  Repaint;
end;

procedure TForm1.FormPaint(Sender: TObject);
var
  g: TGPGraphics;
  p: TGPPen;
  i: Integer;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  p := TGPPen.Create(aclRed, 2);
  g.Clear(aclWhite);
  g.DrawClosedCurve(p, PGPPoint(PtArr), Length(PtArr), tension);
  p.SetWidth(1);
  p.SetColor(aclBlack);
  for i := 0 to Length(PtArr) - 1 do
    g.DrawEllipse(p, PtArr[i].X - 2, PtArr[i].Y - 2, 4, 4);
  g.Free;
  p.Free;
end;

procedure TForm1.TrackBar1Change(Sender: TObject);
begin
  tension := TrackBar1.Position / 10;
  Repaint;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  i := 0;
  SetLength(PtArr, i);
  Repaint;
  Text := IntToStr(i);
end;

end.

表單設計 (DFM)

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 188
  ClientWidth = 264
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  Position = poDesktopCenter
  OnCreate = FormCreate
  OnMouseUp = FormMouseUp
  OnPaint = FormPaint
  PixelsPerInch = 96
  TextHeight = 13
  object Button1: TButton
    Left = 181
    Top = 155
    Width = 75
    Height = 25
    Caption = 'Button1'
    TabOrder = 0
    OnClick = Button1Click
  end
  object TrackBar1: TTrackBar
    Left = 8
    Top = 155
    Width = 167
    Height = 25
    TabOrder = 1
    OnChange = TrackBar1Change
  end

執行效果

DrawCurve vs DrawClosedCurve 差異

閉合曲線配合填充筆刷 (FillClosedCurve) 可繪製任意形狀填充區域。