delphi - Create a button that accepts .PNG images as Glyph

Question

I'm trying to understand how the SpeedButton Glyph property work, I find that the field declared as:

FGlyph: TObject;

While the property as:

property Glyph: TBitmap read GetGlyph write SetGlyph stored HasCustomGlyph;

That put me in a way where I can't understand that code even if I read it line by line, when I was trying to create my own SpeedButton that accepts .PNG images too instead of .bmp images only.

For the first time I was thinking to declare the property as TPicture instead of TBitmap.

Is there any way to create MySpeedButton with Glyph : TPicture?

What I try is below:

TMyButton = class(TSpeedButton)
    private
     //
    FGlyph: TPicture;
    procedure SetGlyph(const Value: TPicture);
    protected
    //
    public
    //
    published
    //
      Property Glyph : TPicture read FGlyph write SetGlyph;
  end;

And the procedure:

procedure TMyButton.SetGlyph(const Value: TPicture);
begin
  FGlyph := Value;
end;

Answer 1

Your SetGlyph() needs to call FGlyph.Assign(Value) instead of FGlyph := Value. Be sure to create FGlyph in the constructor and destroy it in the destructor. Then you can call draw the graphic in an overriden Paint() when Graphic is not empty.

type
  TMyButton = class(TGraphicControl)
  private
    FGlyph: TPicture;
    procedure GlyphChanged(Sender: TObject);
    procedure SetGlyph(const Value: TPicture);
    protected
      procedure Paint; override;
    public
      constructor Create(AOwner: TComponent); override;
      destructor Destroy; override;
    published
      property Glyph : TPicture read FGlyph write SetGlyph;
  end;

constructor TMyButton.Create(AOwner: TComponent);
begin
  inherited;
  FGlyph := TPicture.Create;
  FGlyph.OnChange := GlyphChanged;
end;

destructor TMyButton.Destroy;
begin
  FGlyph.Free;
  inherited;
end;

procedure TMyButton.GlyphChanged(Sender: TObject);
begin
  Invalidate;
end;

procedure TMyButton.SetGlyph(const Value: TPicture);
begin
  FGlyph.Assign(Value):
end;

procedure TMyButton.Paint;
begin
 ...
  if (FGlyph.Graphic <> nil) and (not FGlyph.Graphic.Empty) then
    Canvas.Draw(..., FGlyph.Graphic);
 ... 
end;