multithreading - 如何通过多线程绘画到 TBitmap

Question

为了加快在 Delphi XE2 中绘制位图，我决定采用以下方式

a)创建一个例如。 10 x 线程并仅在线程类内绘制一层位图
b)一旦所有线程完成，使用bitblt函数逐层合并位图

我做了以下实验代码

unit Unit_BitmapThread;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Data.DB, Data.Win.ADODB,  ActiveX;



type PaintBitmapThread = class(TThread)

    private

    FBitmap  : TBitmap;
    FConnection : TAdoConnection;
    fserver, fdatabasename, ftablename, fsqlstr : String;
    protected
     procedure Execute; override;
    public
    constructor Create ( bmp_width, bmp_height : Integer; server, databasename, tablename, sqlstr : String; ThreadId : Integer );
    destructor destroy ; override;

end;



type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private-Deklarationen }
    FAdoConnection : TAdoConnection;
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var    i  : Integer;
    aPaintBitmapThread : PaintBitmapThread;
begin
    for i := 1 to 10 do
         begin
          aPaintBitmapThread :=PaintBitmapThread.Create(100,100,'server','database','table','select *',1);
         end;
end;

{ PaintBitmapThread }

constructor PaintBitmapThread.Create(bmp_width, bmp_height: Integer;
  server, databasename, tablename, sqlstr: String; ThreadId: Integer);
begin
    FBitmap  :=TBitmap.create;
    FConnection :=TAdoConnection.Create(nil);
end;

destructor PaintBitmapThread.destroy;
begin
   FBitmap.Free;
   FConnection.Free;
  inherited;
end;

procedure PaintBitmapThread.Execute;
 var
   ThreadQuery : TADOQuery;
   k : integer;
 begin
   inherited;

   CoInitialize(nil) ; //CoInitialize was not called

   ThreadQuery := TADOQuery.Create(nil) ;
   try
// ADO DB THREAD MUST USE OWN CONNECTION
     ThreadQuery.Connection := FConnection;
//     ThreadQuery.ConnectionString := '????';
//     ThreadQuery.CursorLocation := clUseServer;
//     ThreadQuery.LockType := ltReadOnly;
//     ThreadQuery.CursorType := ctOpenForwardOnly;
     ThreadQuery.SQL.Text := FSQLStr;

//     ThreadQuery.Open;
     while NOT ThreadQuery.Eof and NOT Terminated do
     begin



       //Canvas Does NOT Allow Drawing if not called through Synchronize
       //Synchronize(RefreshCount) ;

       ThreadQuery.Next;
     end;
   finally
     ThreadQuery.Free;
   end;

   CoUninitialize()
end;
end. 

Q : a) 10 条涂装线全部完成后如何检测？
b)如何访问线程[i]并将位图获取到主程序(VCL)进行合并？

最好的解决方案是

if Thread[1] and Thread[2] finished -> newBMP :=  Bitblt( bmp1, bm2);

if also Thread[3]finished -> newBMP :=  Bitblt( newBMP, bm3);
 unit all threads-Bitmaps  are merged

Answer 1

a) How to detect once all 10 painting threads are finished and b) How to access the thread[i] and get the bitmap to the main program (VCL) for merging?

添加 OnTerminate每个线程的事件处理程序。这将在主线程上执行。合并此事件处理程序中的位图。因为它在主线程上执行，所以需要注意同步。

如果事件处理程序是线程类的方法，那么它可以访问线程的私有(private)位图对象。

或者，如果您不想使用事件处理程序，请覆盖 DoTerminate并从那里同步合并方法。