Since the TTabSheets aren't a parent of the form as far as VCL is concerned (didn't want to use dynamic RTL, and plugins made in other languages) I have to handle resizes manually. I do this like below:
var
ChildHandle : DWORD;
begin
If Assigned(pcMain.ActivePage) Then
begin
ChildHandle := FindWindowEx(pcMain.ActivePage.Handle, 0, 'TfrmPluginForm', nil);
If ChildHandle > 0 Then
begin
SetWindowPos(ChildHandle, 0, 0, 0, pcMain.ActivePage.Width, pcMain.ActivePage.Height, SWP_NOZORDER + SWP_NOACTIVATE + SWP_NOCOPYBITS);
end;
end;
Now, my problem is that when the application is resized, all the TGroupBoxes and the TLabels inside the TGroupBoxes flicker. The TLabels that are not inside TGroupboxes are fine and don't flicker.
Things I've tried:
Any ideas?
The only thing I have found to work well is to use the WS_EX_COMPOSITED window style. This is a performance hog so I only enable it when in a sizing loop. It is my experience that, with the built-in controls, in my app, flickering only occurs when resizing forms.
You should first perform a quick test to see if this approach will help you by simply adding the WS_EX_COMPOSITED window style to all your windowed controls. If that works you can consider the more advanced approach below:
Quick hack
procedure EnableComposited(WinControl: TWinControl);
var
i: Integer;
NewExStyle: DWORD;
begin
NewExStyle := GetWindowLong(WinControl.Handle, GWL_EXSTYLE) or WS_EX_COMPOSITED;
SetWindowLong(WinControl.Handle, GWL_EXSTYLE, NewExStyle);
for i := 0 to WinControl.ControlCount-1 do
if WinControl.Controls[i] is TWinControl then
EnableComposited(TWinControl(WinControl.Controls[i]));
end;
Call this, for example, in the OnShow for your TForm, passing the form instance. If that helps then you really should implement it more discerningly. I give you the relevant extracts from my code to illustrate how I did that.
Full code
procedure TMyForm.WMEnterSizeMove(var Message: TMessage);
begin
inherited;
BeginSizing;
end;
procedure TMyForm.WMExitSizeMove(var Message: TMessage);
begin
EndSizing;
inherited;
end;
procedure SetComposited(WinControl: TWinControl; Value: Boolean);
var
ExStyle, NewExStyle: DWORD;
begin
ExStyle := GetWindowLong(WinControl.Handle, GWL_EXSTYLE);
if Value then begin
NewExStyle := ExStyle or WS_EX_COMPOSITED;
end else begin
NewExStyle := ExStyle and not WS_EX_COMPOSITED;
end;
if NewExStyle<>ExStyle then begin
SetWindowLong(WinControl.Handle, GWL_EXSTYLE, NewExStyle);
end;
end;
function TMyForm.SizingCompositionIsPerformed: Boolean;
begin
//see The Old New Thing, Taxes: Remote Desktop Connection and painting
Result := not InRemoteSession;
end;
procedure TMyForm.BeginSizing;
var
UseCompositedWindowStyleExclusively: Boolean;
Control: TControl;
WinControl: TWinControl;
begin
if SizingCompositionIsPerformed then begin
UseCompositedWindowStyleExclusively := Win32MajorVersion>=6;//XP can't handle too many windows with WS_EX_COMPOSITED
for Control in ControlEnumerator(TWinControl) do begin
WinControl := TWinControl(Control);
if UseCompositedWindowStyleExclusively then begin
SetComposited(WinControl, True);
end else begin
if WinControl is TPanel then begin
TPanel(WinControl).FullRepaint := False;
end;
if (WinControl is TCustomGroupBox) or (WinControl is TCustomRadioGroup) or (WinControl is TCustomGrid) then begin
//can't find another way to make these awkward customers stop flickering
SetComposited(WinControl, True);
end else if ControlSupportsDoubleBuffered(WinControl) then begin
WinControl.DoubleBuffered := True;
end;
end;
end;
end;
end;
procedure TMyForm.EndSizing;
var
Control: TControl;
WinControl: TWinControl;
begin
if SizingCompositionIsPerformed then begin
for Control in ControlEnumerator(TWinControl) do begin
WinControl := TWinControl(Control);
if WinControl is TPanel then begin
TPanel(WinControl).FullRepaint := True;
end;
UpdateDoubleBuffered(WinControl);
SetComposited(WinControl, False);
end;
end;
end;
function TMyForm.ControlSupportsDoubleBuffered(Control: TWinControl): Boolean;
const
NotSupportedClasses: array [0..1] of TControlClass = (
TCustomForm,//general policy is not to double buffer forms
TCustomRichEdit//simply fails to draw if double buffered
);
var
i: Integer;
begin
for i := low(NotSupportedClasses) to high(NotSupportedClasses) do begin
if Control is NotSupportedClasses[i] then begin
Result := False;
exit;
end;
end;
Result := True;
end;
procedure TMyForm.UpdateDoubleBuffered(Control: TWinControl);
function ControlIsDoubleBuffered: Boolean;
const
DoubleBufferedClasses: array [0..2] of TControlClass = (
TMyCustomGrid,//flickers when updating
TCustomListView,//flickers when updating
TCustomStatusBar//drawing infidelities , e.g. my main form status bar during file loading
);
var
i: Integer;
begin
if not InRemoteSession then begin
//see The Old New Thing, Taxes: Remote Desktop Connection and painting
for i := low(DoubleBufferedClasses) to high(DoubleBufferedClasses) do begin
if Control is DoubleBufferedClasses[i] then begin
Result := True;
exit;
end;
end;
end;
Result := False;
end;
var
DoubleBuffered: Boolean;
begin
if ControlSupportsDoubleBuffered(Control) then begin
DoubleBuffered := ControlIsDoubleBuffered;
end else begin
DoubleBuffered := False;
end;
Control.DoubleBuffered := DoubleBuffered;
end;
procedure TMyForm.UpdateDoubleBuffered;
var
Control: TControl;
begin
for Control in ControlEnumerator(TWinControl) do begin
UpdateDoubleBuffered(TWinControl(Control));
end;
end;
This won't compile for you, but it should contain some useful ideas. ControlEnumerator is my utility to turn a recursive walk of the child controls into a flat for loop. Note that I also use a custom splitter that calls BeginSizing/EndSizing when it is active.
Another useful trick is to use TStaticText instead of TLabel which you occasionally need to do when you have deep nesting of page controls and panels.
I've used this code to make my app 100% flicker free but it took me ages and ages of experimenting to get it all in place. Hopefully others can find something of use in here.