unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, ActnMan, ActnColorMaps, ExtCtrls, Menus;

type
  TForm1 = class(TForm)
    MainMenu1: TMainMenu;
    N1: TMenuItem;
    mnu_Horizontal: TMenuItem;
    mnu_Vertical: TMenuItem;
    N2: TMenuItem;
    mnu_StartColor: TMenuItem;
    mnu_EndColor: TMenuItem;
    ColorDialog1: TColorDialog;
    procedure Draw(StartColor:TColor;EndColor:TColor;Direction:Integer);
    procedure mnu_StartColorClick(Sender: TObject);
    procedure mnu_VerticalClick(Sender: TObject);
    procedure mnu_HorizontalClick(Sender: TObject);
    procedure mnu_EndColorClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure FormResize(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  StartColor:TColor;
  EndColor:TColor;
  Direction:Integer;
implementation

{$R *.DFM}

procedure TForm1.Draw(StartColor:TColor;EndColor:TColor;Direction:Integer);
var
  i:Integer;
  Dct:TRect;
  c1,c2,c3:byte;
begin
    if Direction=0 then
    begin
        for i:=0 to self.Width-1 do
        begin
            c1:=GetRValue(StartColor)+Trunc(i*(GetRValue(EndColor)-GetRValue(StartColor))/(self.Width-1));
            c2:=GetGValue(StartColor)+Trunc(i*(GetGValue(EndColor)-GetGValue(StartColor))/(self.Width-1));
            c3:=GetBValue(StartColor)+Trunc(i*(GetBValue(EndColor)-GetBValue(StartColor))/(self.Width-1));
            Canvas.Brush.Color:=RGB(c1,c2,c3);
            //每次畫矩形的畫刷顏色
            Dct:=Rect(i,0,i+1,self.Height);
            //每次刷繪的矩形區域
            Canvas.FillRect(Dct);
            //填充顏色
        end;
    end
    else
    begin
        for i:=0 to self.Height-1 do
        begin
            c1:=GetRValue(StartColor)+Trunc(i*(GetRValue(EndColor)-GetRValue(StartColor))/(self.Height-1));
            c2:=GetGValue(StartColor)+Trunc(i*(GetGValue(EndColor)-GetGValue(StartColor))/(self.Height-1));
            c3:=GetBValue(StartColor)+Trunc(i*(GetBValue(EndColor)-GetBValue(StartColor))/(self.Height-1));
            Canvas.Brush.Color:=RGB(c1,c2,c3);
            //每次畫矩形的畫刷顏色
            Dct:=Rect(0,i,self.Width,i+1);
            //每次刷繪的矩形區域
            Canvas.FillRect(Dct);
            //填充顏色
        end;
    end;
end;

procedure TForm1.mnu_StartColorClick(Sender: TObject);
begin
    if ColorDialog1.Execute then
        StartColor:=ColorDialog1.Color;
    Draw(StartColor,EndColor,Direction);
end;

procedure TForm1.mnu_VerticalClick(Sender: TObject);
begin
    Direction:=1;
    Draw(StartColor,EndColor,Direction);
end;

procedure TForm1.mnu_HorizontalClick(Sender: TObject);
begin
    Direction:=0;
    Draw(StartColor,EndColor,Direction);
end;

procedure TForm1.mnu_EndColorClick(Sender: TObject);
begin
    if ColorDialog1.Execute then
        EndColor:=ColorDialog1.Color;
    Draw(StartColor,EndColor,Direction);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
    StartColor:=RGB(0,0,0);
    EndColor:=RGB(255,255,255);
    Direction:=0;
end;

procedure TForm1.FormPaint(Sender: TObject);
begin
    Draw(StartColor,EndColor,Direction);
end;

procedure TForm1.FormResize(Sender: TObject);
begin
    self.Canvas.Refresh;
    Draw(StartColor,EndColor,Direction);
end;

end.