再学 GDI+[92]: TGPImage(12) - 调整图像透明度

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.

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