程序代码如下：
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);
          //每次画矩形的画刷颜色
          Dct:=Rect(i,0,i+1,self.Height);
          //每次刷绘的矩形区域
          Canvas.FillRect(Dct);
          //填充颜色
        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);
          //每次画矩形的画刷颜色
          Dct:=Rect(0,i,self.Width,i+1);
          //每次刷绘的矩形区域
          Canvas.FillRect(Dct);
          //填充颜色
        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.

选择“File”|“Save All”选项，在弹出的对话框中选择合适的文件名保存文件。然后按F9键运行程序，程序运行的初始画面如图1-5所示。
读者可以选择渐变背景的(水平方向和垂直方向)和绘制颜色(起始和终止颜色)，图1-6所示为改变渐变背景方向和绘制颜色后的程序运行结果。
  
            图1-5  程序运行的初始画面                       图1-6  程序运行结果

通过本实例，读者可以学习如何对颜色进行线性插值，并且解决窗体上图形重绘的问题。在设计实际的图形应用程序时，运用这两点可以避免走弯路。
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