VCL TImage + TImageList，透明功能不起作用，或者我在做什么错？

Question

Using Borland C++ Builder 2009

I screen-captured three buttons from a W7 Windows dialog and put them in a TImageList. I load the 3 variants in a TImage, when appropriate.

Image->Picture->Bitmap = NULL ; // Clear previous state
ImageList->GetBitmap(2, Image->Picture->Bitmap) ;

PS: Image->Transparent = True

On Windows 7 and Windows 10 this seems to work properly. BUT I just realized, only because the TForm the TImage is placed on has the exact same background color . (confirmed not to work after I changed the background to lime)

On Windows XP the button doesn't look so great. Since XP seems to have slightly different background color. Mind you, it's also clBtnFace

XP: . . . Windows 7:

I have also experimented with setting BlendColor and DrawingStyle of the TImageList control, combined with Image->Transparent = true or false .

But I can't get it to work.

I captured the Image->Picture->Bitmap->Canvas->Pixels[0][0] value on W7 and put it in ImageList->BlendColor ( ImageList->DrawingStyle = dsFocus or dsSelected ) and so forth, without success.

I also have experimented with explicitly setting Image->Transparent = True again after a ImageList->GetBitmap(2, Image->Picture->Bitmap) and even tried

Image->Picture->Bitmap->TransparentColor =
Image->Picture->Bitmap->Canvas->Pixels[0][0]

without a noticeable effect.

Your thoughts ?

Answer 1

How I said on my comment instead of capture the image from the screen you can try drawing the expand button using the DrawThemeBackground method passing the TDLG_EXPANDOBUTTON part and one of the valid states ( TDLGEBS_NORMAL , TDLGEBS_HOVER , TDLGEBS_PRESSED , etc) . And for Windows XP you can use EBP_NORMALGROUPEXPAND part and one of these states ( EBHC_NORMAL , EBHC_HOT , EBHC_PRESSED )

Check this sample which drawn the expando button in a TImage.

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
#include "Vsstyle.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------


__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  Image1->Canvas->Brush->Color = clBtnFace;
  Image1->Canvas->FillRect(Image1->ClientRect);

  OSVERSIONINFO verwin;
  verwin.dwOSVersionInfoSize=sizeof(verwin);
  if (GetVersionEx(&verwin))
  {
    //Check  the Windows version
    if (verwin.dwMajorVersion >= 6) // is Vista at least?
    {
      HTHEME hTheme = OpenThemeData(Handle, VSCLASS_TASKDIALOG);
      if (hTheme)
      {
          SIZE s;
          //get the size of the  TDLG_EXPANDOBUTTON
          if (GetThemePartSize(hTheme, Image1->Canvas->Handle, TDLG_EXPANDOBUTTON, TDLGEBS_NORMAL, NULL, TS_TRUE, &s) == S_OK)
          {
              TRect pRect = Rect(0, 0, s.cx, s.cy);
              DrawThemeBackground(hTheme, Image1->Canvas->Handle, TDLG_EXPANDOBUTTON, TDLGEBS_NORMAL, &pRect, NULL);
           }
      }
    }
    else
    {
      HTHEME hTheme = OpenThemeData(Handle, VSCLASS_EXPLORERBAR);
      if (hTheme)
      {
          SIZE s;
          //get the size of the  EBP_NORMALGROUPEXPAND
          if (GetThemePartSize(hTheme, Image1->Canvas->Handle, EBP_NORMALGROUPEXPAND, EBHC_NORMAL, NULL, TS_TRUE, &s) == S_OK)
          {
              TRect pRect = Rect(0, 0, s.cx, s.cy);
              DrawThemeBackground(hTheme, Image1->Canvas->Handle, EBP_NORMALGROUPEXPAND, EBHC_NORMAL, &pRect, NULL);
           }
      }
    }
  }
}