Delphi – How to make form transparent while keeping the component visible

delphitransparencytransparent-control

I need to make the program which have one form that contains PNG image with transparent area. Form must be invisible, while image must stay visible and transparent area must stay transparent. The problem is image transparency. In this case, main form is transparent, invisible, while all components/controls stays visible. But, transparent area of PNG image doesn't keep transparency. How to keep transparency?

   procedure MakeTransparent;
   var
   AControl: TControl;
   A, Margin, X, Y, CtlX, CtlY: Integer;
   begin
     Margin    := (Width - ClientWidth) div 2;
     FullRgn   := CreateRectRgn(0, 0, Width, Height);
     X         := Margin;
     Y         := Height - ClientHeight - Margin;
   ClientRgn := CreateRectRgn(X, Y, X + ClientWidth, Y + ClientHeight);
   CombineRgn(FullRgn, FullRgn, ClientRgn, RGN_DIFF);
   for A := 0 to ControlCount - 1 do
   begin
    AControl := Controls[A];
    if (AControl is TWinControl) or (AControl is TGraphicControl) then with        AControl do
   begin
    if Visible then
    begin
      CtlX   := X + Left;
      CtlY   := Y + Top;
      CtlRgn := CreateRectRgn(CtlX, CtlY, CtlX + Width, CtlY + Height);
      CombineRgn(FullRgn, FullRgn, CtlRgn, RGN_OR);
    end;
  end;
  end;
  SetWindowRgn(Handle, FullRgn, True);
  end;



  procedure UndoTransparency;
  begin
   FullRgn := CreateRectRgn(0, 0, Width, Height);
   CombineRgn(FullRgn, FullRgn, FullRgn, RGN_COPY);
   SetWindowRgn(Handle, FullRgn, True);
  end;

Best Answer

Just drop this code with a button in your Form and you'll see your Form with your PNG becoming transparent:

procedure SetTransparent(Aform: TForm; AValue: Boolean);
begin
  Aform.TransparentColor := AValue;
  Aform.TransparentColorValue := Aform.Color;
end;

procedure TForm2.Button1Click(Sender: TObject);
begin
  SetTransparent(Self, True);
end;

Related Solutions

R – Delphi + Transparent forms with parent

You can try not set Parent property directly but use subclassing ...

Suppose TParentForm is parent form and TAlphaForm is form with image.

When creating TAlphaForm instance, pass instance of TParentForm as Owner parameter and change WndProc of owner form in constructor.

Next is example code for TAlphaForm:

type
  TAlphaForm = class(TForm)
  private
    FParentWndProc : TWndMethod;
    FParentForm    : TCustomForm;

    procedure HookWindowProc(var Message: TMessage);

  public
    constructor Create(AOwner : TComponent); override;
    destructor Destroy; override;
  end;

Implementation:

constructor TAlphaForm.Create(AOwner: TComponent);
begin
  inherited;

  if(Assigned(AOwner) and (Owner is TCustomForm)) then begin

    FParentForm := TCustomForm(Owner);
    // Subclass owner window 
    FParentWndProc := FParentForm.WindowProc;
    FParentForm.WindowProc := HookWindowProc;
    // Need to repaint to show initial picture
    if(FParentForm.HandleAllocated) then FParentForm.Invalidate;

  end else begin

    FParentForm := nil;
    FParentWndProc := nil;

  end;

end;

destructor TAlphaForm.Destroy;
begin
  if(Assigned(FParentForm)) then begin
    // Restore original WndProc and repaint to restore original look if available  
    FParentForm.WindowProc := FParentWndProc;
    if(FParentForm.HandleAllocated) then FParentForm.Invalidate;
    FParentForm := nil;
    FParentWndProc := nil;
  end;
  inherited;
end;

procedure TAlphaForm.HookWindowProc(var Message: TMessage);
begin

  if( not (Assigned(FParentForm) and Assigned(FParentWndProc)) )
    then exit;

  FParentWndProc(Message);

  if(Message.Msg = WM_PAINT) then begin
    // Paint alpha image here on Owner's form canvas
    // Here is sample painting
    FParentForm.Canvas.Pen.Width := 3;
    FParentForm.Canvas.Pen.Color := clRed;
    FParentForm.Canvas.Ellipse(FParentForm.ClientRect);
  end else if(Message.Msg = WM_SIZE) then begin 
    // Needed because the whole form must be repainted
    FParentForm.Invalidate;
  end;

end;

For me solution works with this parent form code:

type
  TForm1 = class(TForm)
    Button2: TButton;
    Button3: TButton;
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
    FAlpha : TForm;
  public
    { Public declarations }
    constructor Create(AOwner : TComponent); override;
  end;

Implementation:

procedure TForm1.Button2Click(Sender: TObject);
begin
  if(not Assigned(FAlpha)) then FAlpha := TAlphaForm.Create(Self);
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
  FreeAndNil(FAlpha);
end;

constructor TForm1.Create(AOwner: TComponent);
begin
  inherited;
  FAlpha := nil;
end;

Ios – Make UINavigationBar transparent

If anybody is wondering how to achieve this in iOS 7+, here's a solution (iOS 6 compatible too)

In Objective-C

[self.navigationBar setBackgroundImage:[UIImage new]
                         forBarMetrics:UIBarMetricsDefault];
self.navigationBar.shadowImage = [UIImage new];
self.navigationBar.translucent = YES;

In swift 3 (iOS 10)

self.navigationBar.setBackgroundImage(UIImage(), for: .default)
self.navigationBar.shadowImage = UIImage()
self.navigationBar.isTranslucent = true

In swift 2

self.navigationBar.setBackgroundImage(UIImage(), forBarMetrics: .Default)
self.navigationBar.shadowImage = UIImage()
self.navigationBar.translucent = true

Discussion

Setting translucent to YES on the navigation bar does the trick, due to a behavior discussed in the UINavigationBar documentation. I'll report here the relevant fragment:

If you set this property to YES on a navigation bar with an opaque custom background image, the navigation bar will apply a system opacity less than 1.0 to the image.

Best Answer

Related Solutions

R – Delphi + Transparent forms with parent

Ios – Make UINavigationBar transparent

Discussion

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