再学 GDI+[13]: DrawBezier - 绘制贝塞尔线
本例效果图:



代码文件:
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);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses GDIPOBJ,GDIPAPI;

var
  pts: array[0..3] of TGPPoint = ((X:30;Y:100),(X:120;Y:10),(X:170;Y:150),(X:220;Y:100));
  ptn: Integer = -1;
  f: Boolean;

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.DrawBezier(p, pts[0], pts[1], pts[2], pts[3]);

  p.SetColor(aclBlue);
  for i := 0 to 3 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;
    for i := 0 to 3 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 ptn := i;
    end;
  end;
end;

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

end.
窗体文件:
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
  OnMouseDown = FormMouseDown
  OnMouseMove = FormMouseMove
  OnMouseUp = FormMouseUp
  OnPaint = FormPaint
  PixelsPerInch = 96
  TextHeight = 13
end