I have a project with alot of paint stuff, like components (grids, coloring, shapes), images and so on.
I decided to start the use of GPU acceleration to make the entire solution smoother and faster so a gradual migration from normal GDI (TCanvas) to GPU accelered (TDirect2DCanas) will be planned over the components that makes sense (migrate all rendering components or only those that can really benefit of?).

I started to research around to make initial tests, because I don’t even know if TDirect2DCanvas is what I exactly need. But well I found this post by François (ICS owner) that is basically the same as the Embarcadero doc here.

They both helped me alot to understand, at least the basic. To do a test I builded a component just like the Fraçois post (link above) which is a custom panel with overrided paint events and canvas just like the documentation (another link above).

I also made some changes to have a closer as possible of a TPanel (copy paste from TCustomPanel class and adapted to use TDirect2DCanvas), just with a hardware accelerate with a plus, the code is:

unit CustomPanel;

interface

uses
    Winapi.Messages,
    Winapi.D2D1,
    Winapi.Windows,
    System.Classes,
    System.SysUtils,
    Vcl.Graphics,
    Vcl.ExtCtrls,
    Vcl.Direct2D,
    Vcl.Controls,
    Vcl.Themes;

type
    CustomD2DPanel = class(TPanel)
    private
        FD2DCanvas             : TDirect2DCanvas;
        FPrevRenderTarget      : IntPtr;
        FOnPaint               : TNotifyEvent;
        FOnCreateRenderTarget  : TNotifyEvent;
        function  CreateD2DCanvas: Boolean;
        procedure WMEraseBkGnd(var Msg: TMessage); message WM_ERASEBKGND;
        procedure WMPaint(var Msg: TWMPaint); message WM_PAINT;
        procedure WMSize(var Msg: TWMSize); message WM_SIZE;
        // Bevels?
        procedure D2DFrame3D(ACanvas: TDirect2DCanvas; var Rect: TRect; TopColor, BottomColor: TColor; Width: Integer);
    protected
        procedure CreateWnd; override;
        function  GetRenderTarget : ID2D1HwndRenderTarget;
        procedure TriggerCreateRenderTarget; virtual;
    public
        destructor Destroy; override;
        procedure Paint; override;
        property D2DCanvas             : TDirect2DCanvas
                                                   read  FD2DCanvas;
        property RenderTarget          : ID2D1HwndRenderTarget
                                                   read  GetRenderTarget;
        property OnPaint               : TNotifyEvent
                                                   read  FOnPaint
                                                   write FOnPaint;
        property OnCreateRenderTarget  : TNotifyEvent
                                                   read  FOnCreateRenderTarget
                                                   write FOnCreateRenderTarget;
    end;

    D2DPanel = class(CustomD2DPanel)
    published
        property Align;
        property Anchors;
        property Canvas;
        property Color;
        property D2DCanvas;
        property RenderTarget;
        property BevelEdges;
        property BevelInner;
        property BevelOuter;
        property BevelKind;
        property BevelWidth;
        property BorderWidth;
        property Ctl3D;
        property ParentBackground;
        property ParentCtl3D;
        property OnAlignInsertBefore;
        property OnAlignPosition;
        property OnDockDrop;
        property OnDockOver;
        property OnEnter;
        property OnExit;
        property OnGetSiteInfo;
        property OnKeyDown;
        property OnKeyPress;
        property OnKeyUp;
        property OnUnDock;
        property DragCursor;
        property DragMode;
        property ParentBiDiMode;
        property ParentColor;
        property ParentFont;
        property ParentShowHint;
        property PopupMenu;
        property OnCanResize;
        property OnClick;
        property OnConstrainedResize;
        property OnContextPopup;
        property OnDblClick;
        property OnDragDrop;
        property OnDragOver;
        property OnEndDock;
        property OnEndDrag;
        property OnMouseActivate;
        property OnMouseDown;
        property OnMouseEnter;
        property OnMouseLeave;
        property OnMouseMove;
        property OnMouseUp;
        property OnMouseWheel;
        property OnMouseWheelDown;
        property OnMouseWheelUp;
        property OnResize;
        property OnStartDock;
        property OnStartDrag;
        property OnPaint;
    end;

implementation

{ CustomD2DPanel }

destructor CustomD2DPanel.Destroy;
begin
    FreeAndNil(FD2DCanvas);
    inherited Destroy;
end;

function CustomD2DPanel.CreateD2DCanvas: Boolean;
begin
    try
        FD2DCanvas := TDirect2DCanvas.Create(Handle);
        Result     := TRUE;
    except
        Result     := FALSE;
    end;
    TriggerCreateRenderTarget;
end;

procedure CustomD2DPanel.CreateWnd;
begin
    inherited;
    if (Win32MajorVersion < 6) or (Win32Platform <> VER_PLATFORM_WIN32_NT) then
        raise Exception.Create('Your Windows version do not support Direct2D');
    if not CreateD2DCanvas then
        raise Exception.Create('Unable to create Direct2D canvas');
end;

function CustomD2DPanel.GetRenderTarget: ID2D1HwndRenderTarget;
begin
    if FD2DCanvas <> nil then begin
        Result := FD2DCanvas.RenderTarget as ID2D1HwndRenderTarget;
        if FPrevRenderTarget <> IntPtr(Result) then begin
            FPrevRenderTarget := IntPtr(Result);
            TriggerCreateRenderTarget;
        end;
    end
    else
        Result := nil;
end;

procedure CustomD2DPanel.TriggerCreateRenderTarget;
begin
    if Assigned(FOnCreateRenderTarget) then
        FOnCreateRenderTarget(Self);
end;

procedure CustomD2DPanel.Paint;
const
  Alignments: array[TAlignment] of Longint = (DT_LEFT, DT_RIGHT, DT_CENTER);
  VerticalAlignments: array[TVerticalAlignment] of Longint = (DT_TOP, DT_BOTTOM, DT_VCENTER);
var
  Rect: TRect;
  LColor: TColor;
  LStyle: TCustomStyleServices;
  LDetails: TThemedElementDetails;
  TopColor, BottomColor: TColor;
  BaseColor, BaseTopColor, BaseBottomColor: TColor;
  Flags: Longint;

  procedure AdjustColors(Bevel: TPanelBevel);
  begin
    TopColor := BaseTopColor;
    if Bevel = bvLowered then
      TopColor := BaseBottomColor;
    BottomColor := BaseBottomColor;
    if Bevel = bvLowered then
      BottomColor := BaseTopColor;
  end;

  function CheckParentBackground(AParent: TWinControl): Boolean;
  begin
    if (AParent <> nil) and (AParent is TCustomPanel) then
    begin
      Result := TCustomPanel(AParent).ParentBackground;
      if Result then
        Result := CheckParentBackground(AParent.Parent);
    end
    else
      Result := False;
  end;

begin
  Rect := GetClientRect;

  BaseColor := Color;
  BaseTopColor := clBtnHighlight;
  BaseBottomColor := clBtnShadow;
  LStyle := StyleServices(Self);
  if LStyle.Enabled and (seClient in StyleElements) then
  begin
    LDetails := LStyle.GetElementDetails(tpPanelBackground);
    if LStyle.GetElementColor(LDetails, ecFillColor, LColor) and (LColor <> clNone) then
      BaseColor := LColor;
    LDetails := LStyle.GetElementDetails(tpPanelBevel);
    if LStyle.GetElementColor(LDetails, ecEdgeHighLightColor, LColor) and (LColor <> clNone) then
      BaseTopColor := LColor;
    if LStyle.GetElementColor(LDetails, ecEdgeShadowColor, LColor) and (LColor <> clNone) then
      BaseBottomColor := LColor;
  end;

  if BevelOuter <> bvNone then
  begin
    AdjustColors(BevelOuter);
    D2DFrame3D(D2DCanvas, Rect, TopColor, BottomColor, BevelWidth);
  end;
  if not (LStyle.Enabled and (csParentBackground in ControlStyle)) then
    D2DFrame3D(D2DCanvas, Rect, BaseColor, BaseColor, BorderWidth)
  else
    InflateRect(Rect, -Integer(BorderWidth), -Integer(BorderWidth));
  if BevelInner <> bvNone then
  begin
    AdjustColors(BevelInner);
    D2DFrame3D(D2DCanvas, Rect, TopColor, BottomColor, BevelWidth);
  end;
  with FD2DCanvas do
  begin
    if not LStyle.Enabled or not ParentBackground or not (seClient in StyleElements) or
       (not LStyle.IsSystemStyle and (Parent <> nil) and (Parent is TCustomPanel) and
       TCustomPanel(Parent).DoubleBuffered and not CheckParentBackground(Parent))
    then
    begin
      Brush.Color := BaseColor;
      FillRect(Rect);
    end;

    if ShowCaption and (Caption <> '') then
    begin
      Brush.Style := bsClear;
      Font.Assign(Self.Font);
      Flags := DT_EXPANDTABS or DT_SINGLELINE or
        VerticalAlignments[VerticalAlignment] or Alignments[Alignment];
      Flags := DrawTextBiDiModeFlags(Flags);
      if LStyle.Enabled and (seFont in StyleElements) then
      begin
        LDetails := LStyle.GetElementDetails(tpPanelBackground);
        if not LStyle.GetElementColor(LDetails, ecTextColor, LColor) or (LColor = clNone) then
          LColor := Font.Color;
        LStyle.DrawText(Handle, LDetails, Caption, Rect, TTextFormatFlags(Flags), LColor)
      end
      else
        DrawText(Handle, Caption, -1, Rect, Flags);
    end;
  end;
end;

procedure CustomD2DPanel.WMEraseBkGnd(var Msg: TMessage);
begin
    Msg.Result := 1;
end;

procedure CustomD2DPanel.WMPaint(var Msg: TWMPaint);
var
    PaintStruct: TPaintStruct;
begin
    BeginPaint(Handle, PaintStruct);
    try
        FD2DCanvas.BeginDraw;
        try
            Paint;
        finally
            FD2DCanvas.EndDraw;
        end;
    finally
        EndPaint(Handle, PaintStruct);
    end;
end;

procedure CustomD2DPanel.WMSize(var Msg: TWMSize);
var
    Size: D2D1_SIZE_U;
begin
    if FD2DCanvas <> nil then begin
        Size := D2D1SizeU(Width, Height);
        ID2D1HwndRenderTarget(FD2DCanvas.RenderTarget).Resize(Size);
    end;
    inherited;
end;

procedure CustomD2DPanel.D2DFrame3D(ACanvas: TDirect2DCanvas;
  var Rect: TRect; TopColor, BottomColor: TColor; Width: Integer);

  procedure DoRect;
  var
    TopRight, BottomLeft: TPoint;
  begin
    with ACanvas, Rect do
    begin
      TopRight.X := Right;
      TopRight.Y := Top;
      BottomLeft.X := Left;
      BottomLeft.Y := Bottom;
      Pen.Color := TopColor;
      PolyLine([BottomLeft, TopLeft, TopRight]);
      Pen.Color := BottomColor;
      Dec(BottomLeft.X);
      PolyLine([TopRight, BottomRight, BottomLeft]);
    end;
  end;

begin
  ACanvas.Pen.Width := 1;
  Dec(Rect.Bottom); Dec(Rect.Right);
  while Width > 0 do
  begin
    Dec(Width);
    DoRect;
    InflateRect(Rect, -1, -1);
  end;
  Inc(Rect.Bottom); Inc(Rect.Right);
end;

end.

Apparently it paints over the GPU as suppose to be (don’t made intense tests), but in design time when I drag the custom panel into the Form I have a black panel at design time, which don’t change even changing the Color property, but at run time respects the theme settings (StyleElements.seClient) and Color property (when seClient style disabled of course)… but as I said, at design time what I see is a completely black component… why? Also don’t draw the caption of the component for no reason, I just copied all TCustomPanel.Paint event…

I not see a clearly problem with above code that can give this problems, somente can help?
Also I on the right way? Someone with those developing skill to advise?