再学 GDI+[33]: TGPPen 画笔的几何变换 SetTransform

几何变换也就是 Matrix 变换, 画笔的 Matrix 会忽略 dx、dy 平移参数; 选择 LineCapRound 线帽效果比较好.

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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)
    Panel1: TPanel;
    Button1: TButton;
    TrackBar1: TTrackBar;
    TrackBar2: TTrackBar;
    TrackBar3: TTrackBar;
    TrackBar4: TTrackBar;
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure TrackBar1Change(Sender: TObject);
    procedure TrackBar2Change(Sender: TObject);
    procedure TrackBar3Change(Sender: TObject);
    procedure TrackBar4Change(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses GDIPOBJ, GDIPAPI;

procedure TForm1.FormCreate(Sender: TObject);
const
  n = 40;
begin
  TrackBar1.Min := -n;
  TrackBar1.Max := n;
  TrackBar2.Min := -n;
  TrackBar2.Max := n;
  TrackBar3.Min := -n;
  TrackBar3.Max := n;
  TrackBar4.Min := -n;
  TrackBar4.Max := n;

  TrackBar1.Position := 10;
  TrackBar2.Position := 0;
  TrackBar3.Position := 0;
  TrackBar4.Position := 10;

  Button1.OnClick := FormCreate;
end;

procedure TForm1.FormPaint(Sender: TObject);
var
  g: TGPGraphics;
  b: TGPBrush;
  p: TGPPen;
  matrix: TGPMatrix;
  m11, m12, m21, m22: Single;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  b := TGPHatchBrush.Create(HatchStyleLargeGrid, aclForestGreen);
  p := TGPPen.Create(b, 16);

  m11 := TrackBar1.Position / 10;
  m12 := TrackBar2.Position / 10;
  m21 := TrackBar3.Position / 10;
  m22 := TrackBar4.Position / 10;

  matrix := TGPMatrix.Create(m11, m12, m21, m22, 0, 0);
  p.SetTransform(matrix);
  p.SetStartCap(LineCapRound);
  p.SetEndCap(LineCapRound);

  g.DrawLine(p, 30, 30, ClientWidth - Panel1.Width - 30, ClientHeight - 30);

  matrix.Free;
  b.Free;
  p.Free;
  g.Free;
end;

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

procedure TForm1.TrackBar2Change(Sender: TObject);
begin
  Repaint;
end;

procedure TForm1.TrackBar3Change(Sender: TObject);
begin
  Repaint;
end;

procedure TForm1.TrackBar4Change(Sender: TObject);
begin
  Repaint;
end;

end.

窗体文件:

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object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 184
  ClientWidth = 327
  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 Panel1: TPanel
    Left = 228
    Top = 0
    Width = 99
    Height = 184
    Align = alRight
    TabOrder = 0
    ExplicitLeft = 225
    ExplicitHeight = 170
    object Button1: TButton
      Left = 14
      Top = 8
      Width = 75
      Height = 25
      Caption = #21021#22987#21270
      TabOrder = 0
    end
    object TrackBar1: TTrackBar
      Left = 0
      Top = 39
      Width = 100
      Height = 20
      ShowSelRange = False
      TabOrder = 1
      OnChange = TrackBar1Change
    end
    object TrackBar2: TTrackBar
      Left = 0
      Top = 72
      Width = 100
      Height = 20
      ShowSelRange = False
      TabOrder = 2
      OnChange = TrackBar2Change
    end
    object TrackBar3: TTrackBar
      Left = 0
      Top = 106
      Width = 100
      Height = 20
      ShowSelRange = False
      TabOrder = 3
      OnChange = TrackBar3Change
    end
    object TrackBar4: TTrackBar
      Left = 0
      Top = 140
      Width = 100
      Height = 20
      ShowSelRange = False
      TabOrder = 4
      OnChange = TrackBar4Change
    end
  end
end