再学 GDI+[92]: TGPImage(12) 调整图像透明度

本例效果图:

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代码文件:

---

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    TrackBar1: TTrackBar;
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure TrackBar1Change(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses GDIPOBJ, GDIPAPI;

var
  ColorMatrix: TColorMatrix = (
    (1.0, 0.0, 0.0, 0.0, 0.0),
    (0.0, 1.0, 0.0, 0.0, 0.0),
    (0.0, 0.0, 1.0, 0.0, 0.0),
    (0.0, 0.0, 0.0, 1.0, 0.0),
    (0.0, 0.0, 0.0, 0.0, 1.0));

procedure TForm1.FormCreate(Sender: TObject);
begin
  TrackBar1.Height := 23;
  TrackBar1.ShowSelRange := False;
  TrackBar1.Max := 100;
  TrackBar1.Position := TrackBar1.Max;

  DoubleBuffered := True;
end;

procedure TForm1.FormPaint(Sender: TObject);
var
  g: TGPGraphics;
  img: TGPImage;
  ImageAttributes: TGPImageAttributes;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  img := TGPImage.Create('c:\temp\test.png');

  ImageAttributes := TGPImageAttributes.Create;

  {TColorMatrix 数组的 [3,3] 决定透明度}
  ColorMatrix[3,3] := TrackBar1.Position / 100;
  ImageAttributes.SetColorMatrix(ColorMatrix);

  g.DrawImage(img,
              MakeRect(0, 0, img.GetWidth, img.GetHeight),
              0,
              0,
              img.GetWidth,
              img.GetHeight,
              UnitPixel,
              ImageAttributes
              );

  ImageAttributes.Free;
  img.Free;
  g.Free;
end;

procedure TForm1.TrackBar1Change(Sender: TObject);
begin
  Repaint;
end;

end.

窗体文件:

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object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 267
  ClientWidth = 316
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  Position = poDesktopCenter
  OnCreate = FormCreate
  OnPaint = FormPaint
  PixelsPerInch = 96
  TextHeight = 13
  object TrackBar1: TTrackBar
    Left = 0
    Top = 240
    Width = 305
    Height = 45
    TabOrder = 0
    OnChange = TrackBar1Change
  end
end