unit Main;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
Menus, Dialogs;
type
TMainForm = class(TForm)
MainMenu1: TMainMenu;
Options1: TMenuItem;
AddThread: TMenuItem;
RemoveThread: TMenuItem;
ColorDialog1: TColorDialog;
Add10: TMenuItem;
RemoveAll: TMenuItem;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure AddThreadClick(Sender: TObject);
procedure RemoveThreadClick(Sender: TObject);
procedure Add10Click(Sender: TObject);
procedure RemoveAllClick(Sender: TObject);
private
ThreadList: TList;
public
{ Public declarations }
end;
TDrawThread = class(TThread)
private
FColor: TColor;
FForm: TForm;
public
constructor Create(AForm: TForm; AColor: TColor);
procedure Execute; override;
end;
var
MainForm: TMainForm;
implementation
{$R *.DFM}
{ TDrawThread }
constructor TDrawThread.Create(AForm: TForm; AColor: TColor);
begin
FColor := AColor;
FForm := AForm;
inherited Create(False);
end;
procedure TDrawThread.Execute;
var
P1, P2: TPoint;
procedure GetRandCoords;
var
MaxX, MaxY: Integer;
begin
// initialize P1 and P2 to random points within Form bounds
MaxX := FForm.ClientWidth;
MaxY := FForm.ClientHeight;
P1.x := Random(MaxX);
P2.x := Random(MaxX);
P1.y := Random(MaxY);
P2.y := Random(MaxY);
end;
begin
FreeOnTerminate := True;
// thread runs until it or the application is terminated
while not (Terminated or Application.Terminated) do
begin
GetRandCoords; // initialize P1 and P2
with FForm.Canvas do
begin
Lock; // lock canvas
// only one thread at a time can execute the following code:
Pen.Color := FColor; // set pen color
MoveTo(P1.X, P1.Y); // move to canvas position P1
LineTo(P2.X, P2.Y); // draw a line to position P2
// after the next line executes, another thread will be allowed
// to enter the above code block
Unlock; // unlock canvas
end;
end;
end;
{ TMainForm }
procedure TMainForm.FormCreate(Sender: TObject);
begin
ThreadList := TList.Create;
end;
procedure TMainForm.FormDestroy(Sender: TObject);
begin
RemoveAllClick(nil);
ThreadList.Free;
end;
procedure TMainForm.AddThreadClick(Sender: TObject);
begin
// add a new thread to the list... allow user to choose color
if ColorDialog1.Execute then
ThreadList.Add(TDrawThread.Create(Self, ColorDialog1.Color));
end;
procedure TMainForm.RemoveThreadClick(Sender: TObject);
begin
// terminate the last thread in the list and remove it from list
TDrawThread(ThreadList[ThreadList.Count - 1]).Terminate;
ThreadList.Delete(ThreadList.Count - 1);
end;
procedure TMainForm.Add10Click(Sender: TObject);
var
i: Integer;
begin
// create 10 threads, each with a random color
for i := 1 to 10 do
ThreadList.Add(TDrawThread.Create(Self, Random(MaxInt)));
end;
procedure TMainForm.RemoveAllClick(Sender: TObject);
var
i: Integer;
begin
Cursor := crHourGlass;
try
for i := ThreadList.Count - 1 downto 0 do
begin
TDrawThread(ThreadList[i]).Terminate; // terminate thread
TDrawThread(ThreadList[i]).WaitFor; // make sure thread terminates
end;
ThreadList.Clear;
finally
Cursor := crDefault;
end;
end;
initialization
Randomize; // seed random number generator
end.
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