Re: What is the correct way to response to the wxEVT_DPI_CHANGED event?

Hi,

When I move the application between displays with different DPI, I only 
get breakpoint2 (OnDPIChanged).
When I have the application on a display, and change the DPI of that 
display in the Windows settings, it hits both breakpoints.
I get breakpoint2 first (OnDPIChanged) and then breakpoint1 (via 
OnDisplayChanged). So opposite to what you get.
(Windows 10.0.19045, latest Visual Studio 2022).
Even without breakpoints I can see this behavior, because it shows 
'Display resolution was changed'  in the status bar, and not ''DPI 
changed: ...'.

These events are direct responses to Windows messages (WM_DPICHANGED and 
WM_DISPLAYCHANGE).
We don't have any influence on the order of these events.

Maarten


On 3 Apr 2023 14:41, AsmWarrior wrote:
> Hi, everyone, I still have question about the DPI change handling.
>
> Here is the patch I made to the "display" sample code:
>
> diff --git a/samples/display/display.cpp b/samples/display/display.cpp
> index 58f18de..fb028ef 100644
> --- a/samples/display/display.cpp
> +++ b/samples/display/display.cpp
> @@ -356,6 +356,10 @@ void MyFrame::PopuplateWithDisplayInfo()
>          sizer->Add(new wxStaticText(page, wxID_ANY, "Current: "));
>          sizer->Add(new wxStaticText(page, Display_CurrentMode, 
> currentMode));
>
> +        wxSize dpi = GetDPI();
> +        wxSize newSize = wxWindow::FromDIP(wxSize(250,50));
> +        sizer->Add(new wxButton(page, wxID_ANY, _T("Hello World"), 
> wxDefaultPosition, newSize));
> +
>          sizerTop->Add(new wxButton(page, Display_ResetMode, "&Reset 
> mode"),
>                        wxSizerFlags().Centre().Border());
>  #endif // wxUSE_DISPLAY
>
>
> And now I try to set two breakpoints. The breakpoint1 in the above 
> code, in the line of Add() function call. The breakpoint2 is set 
> inside the function:
>
> void MyFrame::OnDPIChanged(wxDPIChangedEvent& event)
> {
>     wxLogStatus(this, "DPI changed: was %d*%d, now %d*%d",
>                 event.GetOldDPI().x, event.GetOldDPI().y,
>                 event.GetNewDPI().x, event.GetNewDPI().y);
>
>     event.Skip();
> }
> Now, I try to run the executable when the initial DPI scaling is 100%, 
> I first got breakpoint1 hit, and I see the "newSize" is 250*50. Now, I 
> try to change the DPI scaling to 150%, and after that, I got 
> breakpoint1 hit again, I see the value of "newSize" is still 250*50. 
> After that I got the breakpoint2 hit.
>
> I expect that when the second time the breakpoint1 got hit, the 
> newSize value should be 375*75, because I have already changed the DPI 
> scaling.
> Also, I expect that the breakpoint2 should be hit before the 
> breakpoint1 after the DPI changes?
>
> Any one can explain this?
>
> Thanks.
> Asmwarrior
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