含图片的TPopupMenu中TMenuItem闪烁问题排查

问题现象 #

在Delphi开发中，当TPopupMenu中的TMenuItem关联图片后，会出现整个菜单项闪烁的异常现象（注：颜色细微变化属于图片压缩问题，无需关注）。

复现情况 #

• 可稳定复现的系统：3台Windows 7设备（2台物理机、1台虚拟机）
• 无此问题的系统：Windows 10及更高版本

调试排查结论 #

我对Vcl.Menus单元进行了深度调试后发现，闪烁的根源并非绘制操作，而是访问TMenuItem的Canvas属性触发的——哪怕不执行任何绘制逻辑，仅仅读取Canvas的属性（比如Brush.Color）就会引发闪烁。这直接导致常规的双缓冲优化方案无法实施，因为双缓冲通常需要依赖Canvas的CopyRect、BitBlt等操作来实现，而这些操作必然会访问Canvas属性。

示例DFM代码（Delphi 10.2.3） #

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 = {
      494C010101000500040010001000FFFFFFFFFF10FFFFFFFFFFFFFFFF424D3600
      0000000000003600000028000000400000001000000001002000000000000010
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      000000000000CC483F00CC483F00CC483F00CC483F00CC483F00CC48
      3F00CC483F000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      000000000000CC483F00CC483F00CC483F00CC483F00CC483F00CC48
      3F00CC483F000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      0000000000000000000000000000000000000000000000000000000000000000
      000000000000CC483F00CC483F00CC483F00CC483F00CC4
    }
  end
end

内容的提问来源于stack exchange，提问作者CodeX