BGRABitmap图像操作3：用鼠标在窗体画断续的曲线

本文介绍了一个使用BGRABitmap库进行绘图的简单应用程序。该程序能够在窗体上绘制黑色圆点，并通过鼠标操作实现连续绘制，形成简单的画板效果。文章提供了完整的源代码，展示了如何创建位图、响应鼠标事件以及执行绘图操作。

代码：

unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
  BGRABitmap, BGRABitmapTypes;

type

  { TForm1 }

  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
    procedure FormPaint(Sender: TObject);
  private
    { private declarations }
    image: TBGRABitmap;
    procedure DrawBrush(X, Y: Integer);
    procedure PaintImage;

  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  image := TBGRABitmap.Create(640,480,BGRAWhite);  //create a 640x480 image
end;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Button = mbLeft then DrawBrush(X,Y);

end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if ssLeft in Shift then DrawBrush(X,Y);

end;

procedure TForm1.FormPaint(Sender: TObject);
begin
  PaintImage;
end;

procedure TForm1.PaintImage;
begin
  image.Draw(Canvas,0,0,True);
end;

procedure TForm1.DrawBrush(X, Y: Integer);
const radius = 5;
begin
  image.GradientFill(X-radius,Y-radius, X+radius,Y+radius,
    BGRABlack,BGRAPixelTransparent, gtRadial,
    PointF(X,Y), PointF(X+radius,Y), dmDrawWithTransparency);

  PaintImage;
end;

end.