TControl.SetParent

[pyscripter 689]

TControl.SetParent contains the following code:

 

      if not (csLoading in ComponentState) and not (csDesigning in ComponentState)
        and not (csDestroying in ComponentState) and not (csFreeNotification in ComponentState) then
      begin
        if not (csDesigning in Parent.ComponentState) then
          ScaleForPPI(GetParentCurrentDpi);
      end;

Apart from the fact that I would write the if condition as

      if [csLoading, csDesigning, csDestroying, csFreeNotification] * ComponentState = [] then

does anyone have any idea why controls with csFreeNotification are not scaled?   This makes writing per Monitor DPI aware applications much harder.

Edited September 27, 2020 by pyscripter

[Uwe Raabe 2057]

You are not alone:

Parented controls with free notifications aren't scaled

Frame with Assigned PopupMenu is wrong Displayed on high DPI

A scaled form gets resized to design time ClientWidth/ClientHeight when embeded in a parent form

[pyscripter 689]

@Uwe Raabe Thanks!  Good to know I am not the only one bitten by this (should have checked QA),  but bad to know it has not been fixed for quite some time now.  I placed my vote on the first issue.

 

You can work around the bug by manually calling ScaleForPPI(future parent PPI)  before setting the parent but it gets difficult to get right with things like docking.   Embarcadero will face this issue when they try to make the IDE per monitor DPI-aware as promised.    

Edited September 27, 2020 by pyscripter

[pyscripter 689]

This is another tough one to work around:

 

procedure TCustomForm.ScaleForPPIRect(NewPPI: Integer; NewRect: PRect);
var
  LCurrentPixelsPerInch: Integer;
  I: Integer;
  PriorHeight: Integer;
begin
  if not (csDesigning in ComponentState) and
    ((not HandleAllocated and (Parent <> nil)) or (NewPPI < 30)) then
    Exit;

Parented forms with  unallocated handle are not scaled (e.g. page-like controls).  It becomes even harder since TCustomForm.SetParent destroys the handle if the form had no parent.

This is irrespective of FreeNotifications.

Edited September 27, 2020 by pyscripter

[Vincent Parrett 750]

4 hours ago, Uwe Raabe said:

You are not alone:

Parented controls with free notifications aren't scaled

Frame with Assigned PopupMenu is wrong Displayed on high DPI

A scaled form gets resized to design time ClientWidth/ClientHeight when embeded in a parent form

🤦‍♂️ Oh FFS - how many versions do we have to wait for properly functioning high dpi support. The fact that these were reported 3 or 4 years ago and have not been addressed is astounding. Surely if you are working on high dpi support you would look at these issues in your own bug tracking system.  

[pyscripter 689]

The workaround for both issues is to follow a pattern such as this:

Form.SetParent(Panel);
Form.HandleNeeded;
Form.ScaleForPPI(Panel.CurrentPPI);