unit BitmapProducerThread;

interface

uses
  System.Generics.Collections,
  System.Classes,
  System.SyncObjs,
  Vcl.Graphics;

type
  TBitmapParameters = record
    Width : Integer;
    Height : Integer;
    constructor Create( AWidth, AHeight : Integer );
  end;

  TBitmapProducerThread = class( TThread )
  private
    FEvent : TEvent;
    FInputCS : TCriticalSection;
    FOutputCS : TCriticalSection;
    FInputQueue : TQueue<TBitmapParameters>;
    FOutput : TBitmap;
    FOnOutputChanged : TNotifyEvent;
    procedure SetOutput( const Value : TBitmap );
    procedure SetOnOutputChanged( const Value : TNotifyEvent );
    function GetOnOutputChanged : TNotifyEvent;
    procedure DoOutputChanged;
  protected
    procedure Execute; override;
    procedure TerminatedSet; override;
    function GetBitmapParameter : TBitmapParameters;
    procedure DoExecute;
  public
    constructor Create;
    destructor Destroy; override;

    procedure Add( ABitmapParameters : TBitmapParameters );
    procedure Get( ABitmap : TBitmap );

    property OnOutputChanged : TNotifyEvent read GetOnOutputChanged write SetOnOutputChanged;
  end;

implementation

{ TBitmapParameters }

constructor TBitmapParameters.Create( AWidth, AHeight : Integer );
begin
  Width := AWidth;
  Height := AHeight;
end;

{ TBitmapProducerThread }

procedure TBitmapProducerThread.Add( ABitmapParameters : TBitmapParameters );
begin
  FInputCS.Enter;
  try
    FInputQueue.Enqueue( ABitmapParameters );
    FEvent.SetEvent;
  finally
    FInputCS.Leave;
  end;
end;

constructor TBitmapProducerThread.Create;
begin
  FInputCS := TCriticalSection.Create;
  FOutputCS := TCriticalSection.Create;
  FEvent := TEvent.Create( nil, True, False, '' );
  FInputQueue := TQueue<TBitmapParameters>.Create;
  FOutput := TBitmap.Create;
  inherited Create;
end;

destructor TBitmapProducerThread.Destroy;
begin

  inherited;
  FInputQueue.Free;
  FOutput.Free;
  FOutputCS.Free;
  FInputCS.Free;
  FEvent.Free;
end;

procedure TBitmapProducerThread.DoExecute;
var
  LBitmap : TBitmap;
  LParams : TBitmapParameters;
  LIdx : Integer;
begin
  // Parameter aus Queue holen
  LParams := GetBitmapParameter;

  LBitmap := TBitmap.Create;
  try

    // Bitmap erstellen
    LBitmap.Canvas.Lock;
    try
      LBitmap.Width := LParams.Width;
      LBitmap.Height := LParams.Height;

      // 5000 rote Pixel auf ein Bitmap malen
      for LIdx := 1 to 5000 do
        LBitmap.Canvas.Pixels[Random( LBitmap.Width ), Random( LBitmap.Height )] := clRed;

    finally
      LBitmap.Canvas.Unlock;
    end;

    // Bitmap in die Ausgabe schreiben
    SetOutput( LBitmap );

  finally
    LBitmap.Free;
  end;

  // Benachrichtigen
  Synchronize( DoOutputChanged );
end;

procedure TBitmapProducerThread.DoOutputChanged;
var
  LEvent : TNotifyEvent;
begin
  LEvent := OnOutputChanged;
  if Assigned( LEvent )
  then
    LEvent( Self );
end;

procedure TBitmapProducerThread.Execute;
begin
  inherited;
  while not Terminated do
    begin
      FEvent.WaitFor;

      if not Terminated
      then
        begin
          DoExecute;
        end;

    end;
end;

procedure TBitmapProducerThread.Get( ABitmap : TBitmap );
begin
  FOutputCS.Enter;
  try
    if Assigned( FOutput )
    then
      ABitmap.Assign( FOutput );
  finally
    FOutputCS.Leave;
  end;
end;

function TBitmapProducerThread.GetBitmapParameter : TBitmapParameters;
begin
  FInputCS.Enter;
  try
    Result := FInputQueue.Dequeue;
    if ( FInputQueue.Count = 0 ) and not Terminated
    then
      FEvent.ResetEvent;
  finally
    FInputCS.Leave;
  end;
end;

function TBitmapProducerThread.GetOnOutputChanged : TNotifyEvent;
begin
  FOutputCS.Enter;
  try
    Result := FOnOutputChanged;
  finally
    FOutputCS.Leave;
  end;
end;

procedure TBitmapProducerThread.SetOnOutputChanged( const Value : TNotifyEvent );
begin
  FOutputCS.Enter;
  try
    FOnOutputChanged := Value;
  finally
    FOutputCS.Leave;
  end;
end;

procedure TBitmapProducerThread.SetOutput( const Value : TBitmap );
begin
  FOutputCS.Enter;
  try
    FOutput.Assign( Value );
  finally
    FOutputCS.Leave;
  end;
end;

procedure TBitmapProducerThread.TerminatedSet;
begin
  inherited;
  FEvent.SetEvent;
end;

end.

unit FormMain;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, BitmapProducerThread,
  Vcl.StdCtrls;

type
  TForm1 = class( TForm )
    Image1 : TImage;
    Button1 : TButton;
    ListBox1 : TListBox;
    procedure Button1Click( Sender : TObject );
  private
    FBitmapProducer : TBitmapProducerThread;
    procedure BitmapProducerOutputChanged( Sender : TObject );
  public
    procedure AfterConstruction; override;
    procedure BeforeDestruction; override;
  end;

var
  Form1 : TForm1;

implementation

{$R *.dfm}
{ TForm1 }

procedure TForm1.AfterConstruction;
begin
  inherited;
  FBitmapProducer := TBitmapProducerThread.Create;
  FBitmapProducer.OnOutputChanged := BitmapProducerOutputChanged;
end;

procedure TForm1.BeforeDestruction;
begin
  inherited;
  FBitmapProducer.OnOutputChanged := nil;
  FBitmapProducer.Free;
end;

procedure TForm1.BitmapProducerOutputChanged( Sender : TObject );
begin
  FBitmapProducer.Get( Image1.Picture.Bitmap );
end;

procedure TForm1.Button1Click( Sender : TObject );
var
  LIdx : Integer;
begin
  ListBox1.Clear;
  for LIdx := 1 to 200 do
    FBitmapProducer.Add( TBitmapParameters.Create( Image1.Width, Image1.Height ) );
end;

end.

program dp_181416;

uses
  Vcl.Forms,
  FormMain in 'FormMain.pas' {Form1},
  BitmapProducerThread in 'BitmapProducerThread.pas';

{$R *.res}

begin
  ReportMemoryLeaksOnShutdown := True;
  Randomize;
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.