Re-learning gdi+[79]: Area (8)

Matrix Transformations (matrices) are powerful, and this is just a spin.

This example effect chart:

Code files:Unit Unit1;
Interface
Uses
Windows, Messages, sysutils, variants, Classes, Graphics, Controls, Forms,
Dialogs, Stdctrls, Comctrls;
Type
TForm1 = Class (Tform)
Trackbar1:ttrackbar;
Procedure Formpaint (Sender:tobject);
Procedure Formcreate (Sender:tobject);
Procedure Trackbar1change (Sender:tobject);
End
Var
Form1:tform1;
Implementation
{$R *.DFM}
Uses Gdipobj, GDIPAPI;
Procedure Tform1.formcreate (Sender:tobject);
Begin
Trackbar1.min: =-45;
Trackbar1.max: = 45;
DoubleBuffered: = True;
End
Procedure Tform1.formpaint (Sender:tobject);
Var
G:tgpgraphics;
B:tgpbrush;
Rgn:tgpregion;
Matrix:tgpmatrix;
Begin
G: = Tgpgraphics.create (Canvas.handle);
B: = Tgphatchbrush.create (Hatchstylemin, Aclsilver, aclchocolate);
Rgn: = Tgpregion.create (Makerect, ClientWidth-80, ClientHeight-100));
Matrix: = tgpmatrix.create;
Matrix.rotate (trackbar1.position);
Rgn. Transform (Matrix);
G.fillregion (b, RGN);
Matrix.free;
Rgn. Free;
B.free;
G.free;
End
Procedure Tform1.trackbar1change (Sender:tobject);
Begin
Repaint;
End
End.

Form file:object Form1: TForm1
　Left = 0
　Top = 0
　Caption = 'Form1'
　ClientHeight = 174
　ClientWidth = 197
　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 = 151
　　Width = 193
　　Height = 23
　　ShowSelRange = False
　　TabOrder = 0
　　OnChange = TrackBar1Change
　end
end