Update fonts recursively on a Delphi form - windows

Question

I'm trying to iterate all the controls on a form and enable ClearType font smoothing. Something like this:
procedure TForm4.UpdateControls(AParent: TWinControl);
var
I: Integer;
ACtrl: TControl;
tagLOGFONT: TLogFont;
begin
for I := 0 to AParent.ControlCount-1 do
begin
ACtrl:= AParent.Controls[I];
// if ParentFont=False, update the font here...
if ACtrl is TWinControl then
UpdateControls(Ctrl as TWinControl);
end;
end;
Now, is there a easy way to check if ACtrl have a Font property so i can pass the Font.Handle to somethink like:
GetObject(ACtrl.Font.Handle, SizeOf(TLogFont), #tagLOGFONT);
tagLOGFONT.lfQuality := 5;
ACtrl.Font.Handle := CreateFontIndirect(tagLOGFONT);
Thank you in advance.

Answer 1

You use TypInfo unit, more specifically methods IsPublishedProp and GetOrdProp.
In your case, it would be something like:
if IsPublishedProp(ACtrl, 'Font') then
ModifyFont(TFont(GetOrdProp(ACtrl, 'Font')))
A fragment from one of my libraries that should put you on the right path:
function ContainsNonemptyControl(controlParent: TWinControl;
const requiredControlNamePrefix: string;
const ignoreControls: string = ''): boolean;
var
child : TControl;
iControl: integer;
ignored : TStringList;
obj : TObject;
begin
Result := true;
if ignoreControls = '' then
ignored := nil
else begin
ignored := TStringList.Create;
ignored.Text := ignoreControls;
end;
try
for iControl := 0 to controlParent.ControlCount-1 do begin
child := controlParent.Controls[iControl];
if (requiredControlNamePrefix = '') or
SameText(requiredControlNamePrefix, Copy(child.Name, 1,
Length(requiredControlNamePrefix))) then
if (not assigned(ignored)) or (ignored.IndexOf(child.Name) < 0) then
if IsPublishedProp(child, 'Text') and (GetStrProp(child, 'Text') <> '') then
Exit
else if IsPublishedProp(child, 'Lines') then begin
obj := TObject(cardinal(GetOrdProp(child, 'Lines')));
if (obj is TStrings) and (Unwrap(TStrings(obj).Text, child) <> '') then
Exit;
end;
end; //for iControl
finally FreeAndNil(ignored); end;
Result := false;
end; { ContainsNonemptyControl }

Answer 2

There's no need to use RTTI for this. Every TControl descendant has a Font property. At TControl level its visibility is protected but you can use this workaround to access it:
type
THackControl = class(TControl);
ModifyFont(THackControl(AParent.Controls[I]).Font);

Answer 3

One other thing worth mentioning. Every control has a ParentFont property, which - if set - allows the Form's font choice to ripple down to every control. I tend to make sure ParentFont is set true wherever possible, which also makes it easier to theme forms according to the current OS.
Anyway, surely you shouldn't need to do anything to enable ClearType smoothing? It should just happen automatically if you use a TrueType font and the user has enabled the Cleartype "effect".

Answer 4

Here's a C++Builder example of TOndrej's answer:
struct THackControl : TControl
{
__fastcall virtual THackControl(Classes::TComponent* AOwner);
TFont* Font() { return TControl::Font; };
};
for(int ControlIdx = 0; ControlIdx < ControlCount; ++ControlIdx)
{
((THackControl*)Controls[ControlIdx])->Font()->Color = clRed;
}