![]() Then modify the header and source files as shown below (create the OnClick and OnPaint handler's using the Object Inspector). Create a new project and and add a button to the main form (put it near the bottom). The following code example does just that. To demonstrate the flicker phenomena, it's beneficial to slow down the message handling process so the flicker becomes more apparent. In fact, you can change the color of the flicker by changing the Color property of the form. The flicker that you see is caused by BeginPaint erasing the background of your window just before your WM_PAINT handler paints the window. Generally, you paint the window in your WM_PAINT handler sometime after BeginPaint has been called. Your window will remain erased until you paint over it. Your entire window will be erased before BeginPaint returns. Realize that this handler executes when your window calls BeginPaint after receiving a WM_PAINT message. The default handler is is equivalent to executing this code: Whenever the DefWindowProc receives a WM_ERASEBKGND message, it erases the contents of the window by filling the window with the background color of the form. The flicker that you see is caused by the default handler for the WM_ERASEBKGND message. If the WM_PAINT message was sent because you called InvalidateRect, then the window will be marked for erasing if the last argument to InvalidateRect was true. The window will almost always be marked for erasing if Windows sent the WM_PAINT message on its own. Among other things, BeginPaint will send your window a WM_ERASEBKGND if the window is marked for erasing. These API functions might sound foreign to you if you've been programming with OWL, the VCL, or MFC because these frameworks call the functions for you (see TWinControl::PaintHandler in CONTROLS.PAS). You can also ask Windows to send a WM_PAINT message by calling the InvalidateRect API call.Īny window that responds to WM_PAINT messages must call the BeginPaint and EndPaint API functions. ![]() This happens when your program first starts, when you restore or maximize the program, and when the program is uncovered from beneath another program. Windows sends your program WM_PAINT messages to notify you that some part of the screen needs to be repainted. * The wrong way to use TPaintBox or TImageīefore you eliminate flicker, it's helpful to know what it is. * Flicker in TControl and TGraphicControl objects One newsgroup post contained a subject line that read: "TPaintBox wicked flicker, can it be stopped." The answer is yes, and the solution is simple, once you understand what is going on. Q: Eliminate flicker when painting on a form or a TPaintBox control.Ī lot of programmers complain about flicker when they draw on a TPaintBox control, when they draw on the form's Canvas, or when they paint on the Canvas of a control that they have written. RE: Flickering Problem 2ffat (Programmer) 6 Nov 10 13:40 If you couldn't understand my Problem I can give you the source code. Several lines in each slide.but when I solve the flickering problem I have problem with drawing line that should be written.I mean it Doesn't clear previous line. This is a program for simulating mechanism and it should write ![]() Void _fastcall TForm1::FourBarLink1Click(TObject *Sender) Void _fastcall TForm1::Clear1Click(TObject *Sender) Void _fastcall TForm1::Button1Click(TObject *Sender) Void _fastcall TForm1::Timer1Timer(TObject *Sender) Void _fastcall TForm1::FormShow(TObject *Sender) Canvas->DrawFocusRect(Rect) //(0, 0, pBitmap) TRect Rect(0, 0, Form1->Width, Form1->Height) Ĭanvas->CopyRect(Rect, pBitmap->Canvas, Rect) Void _fastcall TForm1::FormPaint(TObject *Sender) pBitmap->Canvas->Rectangle(0,0,ClientWidth, ClientHeight) PBitmap->Width=Form1->Width pBitmap->Height=Form1->Height _fastcall TForm1::TForm1(TComponent* Owner): TForm(Owner) ![]() I solved a flickering problem by writing a piece of code like this. ![]()
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