GDI+ 畫筆樣式教學：SetDashStyle 設定預定義虛線類型

GDI+ 的 TGPPen 類別內建六種預定義的線條樣式，開發者可透過 SetDashStyle 方法快速套用，無需自行定義陣列。這些樣式涵蓋實線、虛線、點線、虛點線等常見需求，適合大多數標準繪圖場景。

DashStyle 列舉值

TDashStyle 列舉定義了以下六種樣式：

• DashStyleSolid：實線
• DashStyleDash：虛線
• DashStyleDot：點線
• DashStyleDashDot：虛點線 (─ · ─ ·)
• DashStyleDashDotDot：虛雙點線 (─ · · ─ · ·)
• DashStyleCustom：自訂樣式 (需搭配 SetDashPattern 使用)

程式碼實作

範例使用 TComboBox 列出所有樣式供選擇，繪製對角線展示效果：

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    ComboBox1: TComboBox;
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure ComboBox1Change(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
uses GDIPOBJ, GDIPAPI, TypInfo;

procedure TForm1.FormCreate(Sender: TObject);
var
  i: Integer;
begin
  for i := 0 to 5 do
    ComboBox1.Items.Add(GetEnumName(TypeInfo(TDashStyle), i));
  ComboBox1.ItemIndex := 0;
end;

procedure TForm1.FormPaint(Sender: TObject);
var
  g: TGPGraphics;
  p: TGPPen;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  g.Clear($FFFFFFFF);
  p := TGPPen.Create(aclLimeGreen, 10);
  p.SetDashStyle(TDashStyle(ComboBox1.ItemIndex));
  g.DrawLine(p, 0, 0, ClientWidth, ClientHeight);
  p.Free;
  g.Free;
end;

procedure TForm1.ComboBox1Change(Sender: TObject);
begin
  Repaint;
end;

end.

表單設計 (DFM)

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 167
  ClientWidth = 242
  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 ComboBox1: TComboBox
    Left = 89
    Top = 8
    Width = 145
    Height = 21
    ItemHeight = 13
    TabOrder = 0
    Text = 'ComboBox1'
    OnChange = ComboBox1Change
  end
end

執行效果

下拉選單切換樣式時，對角線即時更新，直觀對比各預定義虛線樣式的視覺差異。