AlphaBlend in FireMonkey

Question

How can I change AlphaBlend value (of a form) in a FireMonkey Desktop Application? Well It\'s available in VCL Application but I couldn\'t find it in FireMonkey

Answer 1

Since you are looking only for a Windows implementation you must add the WS_EX_LAYERED style to your form and then using the SetLayeredWindowAttributes method set the alpha value based in a value or a color.

Check this implementation, using a interposer class.

type
  TForm   = class(FMX.Forms.TForm)
  private
    FAlphaBlend: Boolean;
    FAlphaBlendValue: Byte;
    FTransparentColor: Boolean;
    FTransparentColorValue: TColor;
    procedure SetAlphaBlend(const Value: Boolean);
    procedure SetAlphaBlendValue(const Value: Byte);
    procedure SetLayeredAttribs;
    procedure SetTransparentColor(const Value: Boolean);
    procedure SetTransparentColorValue(const Value: TColor);
  protected
    property AlphaBlend: Boolean read FAlphaBlend write SetAlphaBlend  default False;
    property AlphaBlendValue: Byte read FAlphaBlendValue write SetAlphaBlendValue default 255;
    property TransparentColor: Boolean read FTransparentColor write SetTransparentColor default False;
    property TransparentColorValue: TColor read FTransparentColorValue write SetTransparentColorValue;
  end;

  TForm1 = class(TForm)
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;


var
  Form1: TForm1;

implementation

{$R *.fmx}

uses
 FMX.Platform.Win,
 Winapi.Windows,
 Vcl.Graphics;

type
  TSetLayeredWindowAttributes = function (Hwnd: THandle; crKey: COLORREF;
    bAlpha: Byte; dwFlags: DWORD): Boolean; stdcall;

var
  SetLayeredWindowAttributes: TSetLayeredWindowAttributes = nil;

procedure TForm1.FormCreate(Sender: TObject);
begin
   @SetLayeredWindowAttributes := GetProcAddress(GetModuleHandle(User32), 'SetLayeredWindowAttributes');
   AlphaBlend:=True;
   AlphaBlendValue:=200;
end;

{ TForm }

procedure TForm.SetAlphaBlend(const Value: Boolean);
begin
  if FAlphaBlend <> Value then
  begin
    FAlphaBlend := Value;
    SetLayeredAttribs;
  end;
end;

procedure TForm.SetAlphaBlendValue(const Value: Byte);
begin
  if FAlphaBlendValue <> Value then
  begin
    FAlphaBlendValue := Value;
    SetLayeredAttribs;
  end;
end;

procedure TForm.SetTransparentColor(const Value: Boolean);
begin
  if FTransparentColor <> Value then
  begin
    FTransparentColor := Value;
    SetLayeredAttribs;
  end;
end;

procedure TForm.SetTransparentColorValue(const Value: TColor);
begin
  if FTransparentColorValue <> Value then
  begin
    FTransparentColorValue := Value;
    SetLayeredAttribs;
  end;
end;

procedure TForm.SetLayeredAttribs;
const
  cUseAlpha: array [Boolean] of Integer = (0, LWA_ALPHA);
  cUseColorKey: array [Boolean] of Integer = (0, LWA_COLORKEY);
var
  AStyle: Integer;
begin
  if not (csDesigning in ComponentState) and
    (Assigned(SetLayeredWindowAttributes))  then
  begin

    AStyle := GetWindowLong( WindowHandleToPlatform(Handle).Wnd, GWL_EXSTYLE);
    if FAlphaBlend or FTransparentColor then
    begin
      if (AStyle and WS_EX_LAYERED) = 0 then
        SetWindowLong(WindowHandleToPlatform(Handle).Wnd, GWL_EXSTYLE, AStyle or WS_EX_LAYERED);
      SetLayeredWindowAttributes(WindowHandleToPlatform(Handle).Wnd, ColorToRGB(FTransparentColorValue), FAlphaBlendValue,
        cUseAlpha[FAlphaBlend] or cUseColorKey[FTransparentColor]);
    end
    else
    begin
      SetWindowLong(WindowHandleToPlatform(Handle).Wnd, GWL_EXSTYLE, AStyle and not WS_EX_LAYERED);
      RedrawWindow(WindowHandleToPlatform(Handle).Wnd, nil, 0, RDW_ERASE or RDW_INVALIDATE or RDW_FRAME or RDW_ALLCHILDREN);
    end;
  end;
end;

Answer 2

To make your form background semitransparent you should set form Transparency property to true and use Fill.Color with alpha value like $AAFFFFFF(with Fill.Kind = bkSolid). in this case form border becomes invisible (at least in Delphi XE2)

if you need to make all components at form semitransparent then place TLayout on form with Align = alContents and set its Opacity property to required value.

if you need semitransparent window with alpha blend as it was in VCL you can use the same methods (for Windows platform) as getWindowLong/SetWindowLong. Set transparency back to false and use code like this in form OnCreate event handler:

implementation
uses fmx.platform.win, winapi.windows;
{$R *.fmx}

procedure TMainForm.FormCreate(Sender: TObject);
var h : HWND;
    aStyle : integer;
    alphaValue : byte;
begin
    h := WindowHandleToPlatform(self.Handle).Wnd;
    AStyle := GetWindowLong(h, GWL_EXSTYLE);
    SetWindowLong(h, GWL_EXSTYLE, AStyle or WS_EX_LAYERED);


    AlphaValue := 125;
    SetLayeredWindowAttributes(h, 0, alphaValue, LWA_ALPHA);
end;

of course all your components become trasparent too.