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GDI+ 貝茲曲線群組繪製：DrawBeziers 多段連續曲線

編輯：Delphi

DrawBeziers 方法一次繪製一組連續的三次貝茲曲線。點陣列需包含 3n+1 個點：第一點為起點，後續每三點定義一段曲線 (兩控制點 + 一終點)，終點自動成為下一段的起點，實現平滑連續的複雜曲線路徑。

參數說明

g.DrawBeziers(p, PGPPoint(pts), Length(pts));

pts：TGPPoint 動態陣列，長度必須為 3n+1 (如 4, 7, 10, 13...)
每段曲線消耗 3 點：控制點1、控制點2、終點

程式碼實作

互動式編輯器：按住 Ctrl 點擊新增控制點，拖曳現有點調整曲線，即時預覽：

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    procedure FormPaint(Sender: TObject);
    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 FormCreate(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

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

var
  pts: array of TGPPoint;
  ptn: Integer = -1;
  f: Boolean;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Text := '按住 Ctrl 鍵可添加點';
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);
  g.DrawBeziers(p, PGPPoint(pts), Length(pts));
  p.SetColor(aclBlue);
  for i := Low(pts) to High(pts) do
    g.DrawRectangle(p, MakeRect(Rect(pts[i].X - 2, pts[i].Y - 2, pts[i].X + 2, pts[i].Y + 2)));
  g.Free;
  p.Free;
end;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  f := True;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
var
  R: TRect;
  i: Integer;
begin
  if f then
  begin
    if ptn = -1 then Exit;
    pts[ptn].X := X;
    pts[ptn].Y := Y;
    Repaint;
  end
  else
  begin
    ptn := -1;
    Cursor := crDefault;
    for i := Low(pts) to High(pts) do
    begin
      R := Rect(pts[i].X - 2, pts[i].Y - 2, pts[i].X + 2, pts[i].Y + 2);
      if PtInRect(R, Point(X, Y)) then
      begin
        ptn := i;
        Cursor := crHandPoint;
      end;
    end;
  end;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  f := False;
  if ssCtrl in Shift then
  begin
    SetLength(pts, Length(pts) + 1);
    pts[High(pts)].X := X;
    pts[High(pts)].Y := Y;
    Canvas.Pen.Color := clBlue;
    Canvas.Rectangle(X - 2, Y - 2, X + 2, Y + 2);
    { 點數為 3n+1 時才能構成完整曲線 }
    if Length(pts) mod 3 = 1 then Repaint;
  end;
end;

end.

表單設計 (DFM)

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 188
  ClientWidth = 254
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  Position = poDesktopCenter
  OnCreate = FormCreate
  OnMouseDown = FormMouseDown
  OnMouseMove = FormMouseMove
  OnMouseUp = FormMouseUp
  OnPaint = FormPaint
  PixelsPerInch = 96
  TextHeight = 13
end