再学 GDI+[17]: FillRectangle、ColorRefToARGB、TGPSolidBrush 和颜色透明度

本例效果图:

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代码文件:

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unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, ComCtrls, StdCtrls, ExtCtrls;



type

  TForm1 = class(TForm)

    ColorListBox1: TColorListBox;

    TrackBar1: TTrackBar;

    procedure FormCreate(Sender: TObject);

    procedure FormPaint(Sender: TObject);

    procedure ColorListBox1Click(Sender: TObject);

    procedure TrackBar1Change(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



uses GDIPOBJ,GDIPAPI;



procedure TForm1.FormCreate(Sender: TObject);

begin

  Self.Position := poDesktopCenter;

  ColorListBox1.Align := alRight;

  TrackBar1.ShowSelRange := False;

  TrackBar1.PageSize := 20;

  TrackBar1.Min := 0;

  TrackBar1.Max := 255;

  TrackBar1.Position := TrackBar1.Max;

end;



procedure TForm1.FormPaint(Sender: TObject);

var

  g: TGPGraphics;

  r: TGPRect;

  sb: TGPSolidBrush;

  clr: TGPColor;

  Alpha: Byte;

begin

  g := TGPGraphics.Create(Canvas.Handle);

  g.Clear(MakeColor(255,255,255));

  r := MakeRect(20, 20, 200, 150);

  clr := ColorRefToARGB(ColorListBox1.Selected);

  Alpha := TrackBar1.Position;

  clr := MakeColor(Alpha, GetRed(clr), GetGreen(clr), GetBlue(clr));

  sb := TGPSolidBrush.Create(clr);



  g.FillRectangle(sb, r);



  sb.Free;

  g.Free;

end;



procedure TForm1.ColorListBox1Click(Sender: TObject);

begin

  Repaint;

end;



procedure TForm1.TrackBar1Change(Sender: TObject);

begin

  Repaint;

  Text := Format('透明度: %d', [TrackBar1.Position]);

end;



end.


 
   

窗体文件:

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object Form1: TForm1

  Left = 0

  Top = 0

  Caption = 'Form1'

  ClientHeight = 206

  ClientWidth = 339

  Color = clBtnFace

  Font.Charset = DEFAULT_CHARSET

  Font.Color = clWindowText

  Font.Height = -11

  Font.Name = 'Tahoma'

  Font.Style = []

  OldCreateOrder = False

  OnCreate = FormCreate

  OnPaint = FormPaint

  PixelsPerInch = 96

  TextHeight = 13

  object ColorListBox1: TColorListBox

    Left = 248

    Top = 0

    Width = 91

    Height = 206

    Align = alRight

    ItemHeight = 16

    TabOrder = 0

    OnClick = ColorListBox1Click

  end

  object TrackBar1: TTrackBar

    Left = 0

    Top = 184

    Width = 249

    Height = 45

    TabOrder = 1

    OnChange = TrackBar1Change

  end

end