delphi – Firemonkey：TBitmap.Canvas绘图方法没有可见的结果.

我/我构建一个自定义的FireMonkey GUI控件.我想将控件呈现给后台缓冲区.后台缓冲区将在控件的画布上绘制.

>后台缓冲区是Fmx.TBitmap对象.
>我正在使用后台缓冲区,因为控制渲染代码涉及很少,每次重新绘制控件时都不需要调用.只有当某些控件属性发生更改时,才会更新后台缓冲区.

问题

BackBuffer.Canvas绘图操作没有可见效果.但是,清除位图或单独设置位图像素的值可以按预期工作.

由于某种原因,BackBuffer.Canvas对象不会在后缓冲区位图上绘制.

>我想我已经正确设置了所需的Canvas.Fill属性.
>我检查的所有画布属性似乎都是正确的. (画布宽度/高度/等)

在包含一些线索的情况下,我已经提取了相关代码.

TMyControl(TControl)
private
protected
  BackBuffer : TBitmap;
  procedure Paint; override;
  procedure Resize; override;
public  
  constructor Create(AOwner: TComponent); override;
end;


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

  BackBuffer := TBitmap.Create(10,10);
end;

procedure TFxSampleDisplay.Resize;
var
  w,h : integer;
begin
  inherited;

  // Ensure BackBuffer is the same size as the control. 
  w := round(BoundsRect.Width);
  h := round(BoundsRect.Height);
  BackBuffer.SetSize(w,h);  
end;


procedure TMyControl.Paint;
var
  r : TRectF; 
begin
  inherited;

  //******** This has visible results ********
  BackBuffer.Clear($1100ff00);          // Fill with semi-opaque green background
  BackBuffer.Pixels[2,2] := $ffff0000;  // Draw a red pixel


  //******** This doesn't have visible results ********
  r.Left   := 0;
  r.Top    := 0;
  r.Right  := 50;
  r.Bottom := 50;
  BackBuffer.Canvas.Fill.Color := $ffff0000;          // Set fill to RED. 
  BackBuffer.Canvas.Fill.Kind  := TBrushKind.bkSolid; 
  BackBuffer.Canvas.FillRect(r,10,AllCorners,1);


  //********  Draw the backbuffer on to the controls canvas ******** 
  Canvas.DrawBitmap(BackBuffer,BoundsRect,1);


end;