Mega Code Archive
How to paint a moving progress bar using a background thread
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Title: How to paint a moving progress bar using a background thread
interface
uses
Classes, Windows, Controls, Graphics;
type
TAnimationThread = class(TThread)
private
{ Private declarations }
FWnd: HWND;
FPaintRect: TRect;
FbkColor, FfgColor: TColor;
FInterval: integer;
protected
procedure Execute; override;
public
constructor Create(paintsurface : TWinControl; {Control to paint on }
paintrect : TRect; {area for animation bar }
bkColor, barcolor : TColor; {colors to use }
interval : integer); {wait in msecs between
paints}
end;
implementation
constructor TAnimationThread.Create(paintsurface : TWinControl;
paintrect : TRect; bkColor, barcolor : TColor; interval : integer);
begin
inherited Create(True);
FWnd := paintsurface.Handle;
FPaintRect := paintrect;
FbkColor := bkColor;
FfgColor := barColor;
FInterval := interval;
FreeOnterminate := True;
Resume;
end; { TAnimationThread.Create }
procedure TAnimationThread.Execute;
var
image : TBitmap;
DC : HDC;
left, right : integer;
increment : integer;
imagerect : TRect;
state : (incRight, incLeft, decLeft, decRight);
begin
Image := TBitmap.Create;
try
with Image do
begin
Width := FPaintRect.Right - FPaintRect.Left;
Height := FPaintRect.Bottom - FPaintRect.Top;
imagerect := Rect(0, 0, Width, Height);
end; { with }
left := 0;
right := 0;
increment := imagerect.right div 50;
state := Low(State);
while not Terminated do
begin
with Image.Canvas do
begin
Brush.Color := FbkColor;
FillRect(imagerect);
case state of
incRight:
begin
Inc(right, increment);
if right imagerect.right then
begin
right := imagerect.right;
Inc(state);
end; { if }
end; { Case incRight }
incLeft:
begin
Inc(left, increment);
if left = right then
begin
left := right;
Inc(state);
end; { if }
end; { Case incLeft }
decLeft:
begin
Dec(left, increment);
if left = 0 then
begin
left := 0;
Inc(state);
end; { if }
end; { Case decLeft }
decRight:
begin
Dec(right, increment);
if right = 0 then
begin
right := 0;
state := incRight;
end; { if }
end; { Case decLeft }
end; { Case }
Brush.Color := FfgColor;
FillRect(Rect(left, imagerect.top, right, imagerect.bottom));
end; { with }
DC := GetDC(FWnd);
if DC 0 then
try
BitBlt(DC,
FPaintRect.Left,
FPaintRect.Top,
imagerect.right,
imagerect.bottom,
Image.Canvas.handle,
0, 0,
SRCCOPY);
finally
ReleaseDC(FWnd, DC);
end;
Sleep(FInterval);
end; { While }
finally
Image.Free;
end;
InvalidateRect(FWnd, nil, True);
end; { TAnimationThread.Execute }
end.
{Usage:
Place a TPanel on a form, size it as appropriate.Create an instance of the
TanimationThread call like this: procedure TForm1.Button1Click(Sender : TObject);
}
var
ani : TAnimationThread;
r : TRect;
begin
r := panel1.clientrect;
InflateRect(r, - panel1.bevelwidth, - panel1.bevelwidth);
ani := TanimationThread.Create(panel1, r, panel1.color, clBlue, 25);
Button1.Enabled := False;
Application.ProcessMessages;
Sleep(30000); // replace with query.Open or such
Button1.Enabled := True;
ani.Terminate;
ShowMessage('Done');
end;
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