GDI+ 直線繪製基礎：DrawLine 四種參數重載詳解

DrawLine 提供四種參數重載，支援整數/浮點座標與點結構體傳遞，是 GDI+ 最基礎的繪圖原語。理解重載差異有助於選擇最適合場景的調用方式。

四種重載形式

g.DrawLine(p, x1, y1, x2, y2: Integer);        { 整數座標 }
g.DrawLine(p, pt1, pt2: TGPPoint);             { 整數點結構體 }
g.DrawLine(p, x1, y1, x2, y2: Single);         { 浮點座標 }
g.DrawLine(p, pt1, pt2: TGPPointF);            { 浮點點結構體 }

程式碼實作

同一畫筆繪製四條線，分別展示四種重載：

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    procedure FormPaint(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

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

procedure TForm1.FormPaint(Sender: TObject);
var
  g: TGPGraphics;
  p: TGPPen;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  p := TGPPen.Create(MakeColor(255, 0, 0), 2);
  g.Clear(MakeColor(255, 255, 255));
  g.DrawLine(p, 20, 40, 200, 40);                    { 整數座標 }
  g.DrawLine(p, MakePoint(20, 60), MakePoint(200, 60)); { 整數點 }
  g.DrawLine(p, 20.9, 80.0, 200.9, 80.0);            { 浮點座標 }
  g.DrawLine(p, MakePoint(20.9, 100.0), MakePoint(200.9, 100.0)); { 浮點點 }
  g.Free;
  p.Free;
end;

end.

執行效果

重載選擇指南

MakePoint / MakePointF 輔助函數可簡化結構體構建，建議統一使用。