drawing wxBitmap: doesn't refresh before every time it draws

[greekfellows]

Code: Select all

void bmImage::paintEvent(wxPaintEvent &event) {
	wxPaintDC dc(this);
	render(dc);
}

void bmImage::paintNow() {
	wxClientDC dc(this);
	render(dc);
}

void bmImage::render(wxDC& dc) {
	bitmap = wxBitmap(aswxImage);
	dc.Clear();
	dc.SetUserScale(((bmImageFrame*)this->GetParent())->scale[0], ((bmImageFrame*)this->GetParent())->scale[1]);
	dc.DrawBitmap(bitmap, wxPoint(0, 0), false);
}

bmImage derives from wxPanel. I want the image to be drawn on a clean, refreshed background every time.
But before I scale the loaded image, it looks like this: (the image is clipped because of resized window)

And after I scale the image then resize the window, it looks like this:

How should I fix this so that it redraws the scaled image over clean background? Obviously there is a problem with drawing and clearing canvas here.

[PB]

If there are issues with parts of window not being properly painted after its resize, it can be a good idea to create the window in question with wxFULL_REPAINT_ON_RESIZE flag.

[eranif]

Some tips:
1. Make sure you also capture the. Erase background event. Inside it, clear the paint area by drAwing a rectangle with size of the panel
2. Use wxBufferedPaintDC in In OnPaint event handler and use it to draw
3. Capture the ON_SIZE event and simply call refresh

Eran

[greekfellows]

Thanks for answers so far @eranif @PB!

I intercepted the wxEVT_SIZE event and called event.Skip() there so it refreshes every time it draws now, that's fine,
but now I have a flickering white screen (I used white to repaint a full-size rectangle)...

Code: Select all

void bmImage::paintEvent(wxPaintEvent &event) {
	wxBufferedPaintDC dc(this);
	render(dc);
}

void bmImage::paintNow() {
	wxClientDC dc(this);
	render(dc);
}

void bmImage::render(wxDC& dc) {
	bitmap = wxBitmap(aswxImage);
	dc.SetBackground(*wxWHITE_BRUSH);
	dc.Clear();
	wxPoint orgp = dc.GetLogicalOrigin();
	dc.SetLogicalOrigin(((bmImageFrame*)this->GetParent())->scroll[0], ((bmImageFrame*)this->GetParent())->scroll[1]);
	dc.SetUserScale(((bmImageFrame*)this->GetParent())->scale[0], ((bmImageFrame*)this->GetParent())->scale[1]);
	dc.DrawBitmap(bitmap, wxPoint(0, 0), false);
	dc.SetLogicalOrigin(orgp.x, orgp.y);
	dc.SetUserScale(1.0f, 1.0f);
	dc.SetPen(*wxWHITE_PEN);
	dc.DrawText(wxString("w: " + std::to_string(GetSize().GetWidth()) + ", h: " + std::to_string(GetSize().GetHeight()) + "\nx: " + std::to_string(((bmImageFrame*)this->GetParent())->scroll[0]) + ", y: " + std::to_string(((bmImageFrame*)this->GetParent())->scroll[1])), 100, 100);
}

[doublemax]

Do you have a wxEraseEvent handler? If yes, it should be completely empty. Do not clear the background, do not call event.Skip().

If you're using wx 3.x, you don't need an wxEraseEvent handler at all, just call wxWindow::SetBackgroundStyle(wxBG_STYLE_PAINT) on the window.

[eranif]

1. Make sure you also capture the. Erase background event. Inside it, clear the paint area by drAwing a rectangle with size of the panel

Hmm, I gave a bad advise here...
You should capture the EVT_ERASE_BACKGROUND event, but do nothing in it - this will remove the flickering
Also, avoid using wxClientDC. If you need to force a paint now, simply call 'Refresh()' this will trigger a call to OnPaint/OnErase

So your function 'paintNow'' should look like this:

Code: Select all

void bmImage::paintNow() {
   Refresh(); // triggers a 'OnPaint' event
}

Eran

[greekfellows]

Thanks! @eranif @doublemax

Used Refresh() in paintNow() and called SetBackgroundStyle().
Now it doesn't flicker at all.