![]() ![]() 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) Procedure TMyForm.I solved a flickering problem by writing a piece of code like this. Procedure TMyForm.MyImage1Click(Sender: TObject) With TGraphicControlAccess(Self).Canvas do TGraphicControlAccess = class(TGraphicControl) Procedure TMyImage.SetShowRectangle(Value: Boolean) Property ShowRectangle: Boolean read FShowRectangle write SetShowRectangle Procedure SetShowRectangle(Value: Boolean) (PaintBox2.ClientRect) Īlternatively, you can derive a new class from TImage and override its virtual Paint() method to draw the rectangle after default drawing. Procedure TMyForm.PaintBox2Paint(Sender: TObject) Procedure TMyForm.PaintBox1Paint(Sender: TObject) Procedure TMyForm.PaintBox2Click(Sender: TObject) For example: procedure TMyForm.PaintBox1Click(Sender: TObject) ![]() You can then draw a red rectangle on top of the image when needed. That is all a TImage really does (it holds a TGraphic that is drawn onto its Canvas when painted). Load your image into an appropriate TGraphic class ( TBitmap, TIcon, TPNGImage, etc) and then draw it onto the TPaintBox in its OnPaint event. ![]() I would suggest using a TPaintBox instead of a TImage. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |