使用图像

Question

TMenuItem内的TPopupMenu如果包含图片，则会闪烁。

请注意，整个项目都是闪烁的，而不仅仅是图像区域（不要介意稍微改变颜色，这是一个压缩问题）。

我已经在这个问题上工作了几个小时，但遗憾的是找不到解决方案，或者至少找不到解释。这个问题类似于我的上一个问题（Remove flickering from TSpeedButton），所以我猜不是每个人都能重现这个问题。我可以在3个不同的Windows 7系统（2个物理，1个VM）上重现它，但不能在我的Windows 10系统上重现（与TSpeedButton闪烁相同）。即使你无法重现它，也许你可以想出一个理由和解决方案。

我调试了Vcl单元（主要是Vcl.Menus），以为我可以为图像创建一个自定义的双缓冲绘制方法。但事实证明，这幅画不是问题。来自TMenuItem画布的阅读是

画布在TPopupList.WndProc中创建。如果我删除了行DrawMenuItem()，则闪烁消失（同样是图像）。这是奇怪的部分。如果我访问画布的某些属性（没有在其上绘制任何东西），闪烁又回来了！例如，添加以下行（而不是DrawMenuItem()）会导致闪烁，而不会绘制任何图像：

OutputDebugString(PChar(IntToHex(Canvas.Brush.Color)));

我无法在不访问画布内容（使用Canvas.CopyRect或BitBlt复制）或至少读取一种像素颜色的情况下创建双缓冲解决方案。

这是一个样本dfm（使用Delphi 10.2.3创建）：

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 295
  ClientWidth = 341
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  PopupMenu = PopupMenu1
  PixelsPerInch = 96
  TextHeight = 13
  object PopupMenu1: TPopupMenu
    Images = ImageList1
    Left = 168
    Top = 152
    object Firstline1: TMenuItem
      Caption = 'First line'
      ImageIndex = 0
    end
    object Secondline1: TMenuItem
      Caption = 'Second line'
      ImageIndex = 0
    end
    object hirdline1: TMenuItem
      Caption = 'Third line'
      ImageIndex = 0
    end
  end
  object ImageList1: TImageList
    Left = 96
    Top = 152
    Bitmap = {
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      000000000000000000000000000000000000424D3E000000000000003E000000
      2800000040000000100000000100010000000000800000000000000000000000
      000000000000000000000000FFFFFF00FFFF000000000000FFFF000000000000
      FC07000000000000FC07000000000000FC07000000000000FC07000000000000
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      000000000000}
  end
end

此外，我已经浏览了我安装的应用程序并尝试了他们的上下文菜单。只有少数人在闪烁，其中大部分都没有。进一步调查显示，所有受影响的应用程序都是使用Delphi创建的！对我来说，这似乎是一个普遍的德尔福问题，一直存在，但没有人关心它 - 也许是因为它不会影响所有系统。

造成这个问题的原因是什么？是否有适当的解决方案或至少有解决方法？