問題描述

我正在創建一個非常簡單的 Win32 C++ 應用程序，其唯一目的是僅顯示半透明的 PNG.窗口不應有任何鍍鉻，并且所有不透明度都應在 PNG 本身中控制.

I'm creating what should be a very simple Win32 C++ app whose sole purpose it to ONLY display a semi-transparent PNG. The window shouldn't have any chrome, and all the opacity should be controlled in the PNG itself.

我的問題是當窗口下的內容發生變化時窗口不會重新繪制，因此 PNG 的透明區域卡住"了應用程序最初啟動時窗口下的內容.

My problem is that the window doesn't repaint when the content under the window changes, so the transparent areas of the PNG are "stuck" with what was under the window when the application was initially started.

這是我設置新窗口的行:

Here's the line where I setup the new window:

hWnd = CreateWindowEx(WS_EX_TOPMOST, szWindowClass, szTitle, WS_POPUP, 0, height/2 - 20, 40, 102, NULL, NULL, hInstance, 0);

對于 RegisterClassEx 的調用，我為后臺設置了這個:

For the call to RegisterClassEx, I have this set for the background:

wcex.hbrBackground = (HBRUSH)0;

這是我的 WM_PAINT 消息處理程序:

Here is my handler for WM_PAINT message:

 case WM_PAINT:
 {
   hdc = BeginPaint(hWnd, &ps);
   Gdiplus::Graphics graphics(hdc);
   graphics.DrawImage(*m_pBitmap, 0, 0);
   EndPaint(hWnd, &ps);
   break;
 }

需要注意的一點是，應用程序始終停靠在屏幕左側并且不會移動.但是，應用程序下方的內容可能會隨著用戶打開、關閉或移動其下方的窗口而發生變化.

One thing to note is that the application is always docked to the left of the screen and doesn't move. But, what's underneath the application may change as the user opens, closes or moves windows under it.

當應用程序第一次啟動時，它看起來很完美.PNG 的透明(和半透明)部分完美地顯示出來.但是，當應用程序下面的背景發生變化時，背景不會更新，它只是與應用程序剛啟動時保持不變.實際上，WM_PAINT(或 WM_ERASEBKGND 在背景變化時不會被調用).

When the application first starts, it looks perfect. The transparent (and simi-transparent) parts of the PNG show through perfectly. BUT, when the background underneath the application changes, the background DOESN'T update, it just stays the same from when the application first started. In fact, WM_PAINT (or WM_ERASEBKGND does not get called when the background changes).

我已經玩了很長一段時間，并且已經接近 100% 正確，但還沒有完全正確.例如，我嘗試將背景設置為 (HBRUSH) NULL_BRUSH，并且嘗試處理 WM_ERASEBKGND.

I've been playing with this for quite a while and have gotten close to getting 100% right, but not quite there. For instance, I've tried setting the background to (HBRUSH) NULL_BRUSH and I've tried handling WM_ERASEBKGND.

當窗口下的內容發生變化時，如何讓窗口重新繪制?

What can be done to get the window to repaint when the contents under it changes?

推薦答案

通過使用本系列第 1 部分和第 2 部分中的代碼，我能夠完全按照自己的意愿行事:

I was able to do exactly what I wanted by using the code from Part 1 and Part 2 of this series:

使用 C++ 顯示啟動畫面

• 第 1 部分: 創建 HBITMAP ^存檔
• 第 2 部分: 顯示窗口 ^存檔

那些博客文章談論的是在 Win32 C++ 中顯示啟動畫面，但這與我需要做的幾乎相同.我相信我缺少的部分是，我需要使用 UpdateLayeredWindow 函數和正確的 BLENDFUNCTION 參數.我將粘貼下面的 SetSplashImage 方法，該方法可以在上面鏈接的第 2 部分中找到:

Those blog posts are talking about displaying a splash screen in Win32 C++, but it was almost identical to what I needed to do. I believe the part that I was missing was that instead of just painting the PNG to the window using GDI+, I needed to use the UpdateLayeredWindow function with the proper BLENDFUNCTION parameter. I'll paste the SetSplashImage method below, which can be found in Part 2 in the link above:

void SetSplashImage(HWND hwndSplash, HBITMAP hbmpSplash)
{
  // get the size of the bitmap
  BITMAP bm;
  GetObject(hbmpSplash, sizeof(bm), &bm);
  SIZE sizeSplash = { bm.bmWidth, bm.bmHeight };

  // get the primary monitor's info
  POINT ptZero = { 0 };
  HMONITOR hmonPrimary = MonitorFromPoint(ptZero, MONITOR_DEFAULTTOPRIMARY);
  MONITORINFO monitorinfo = { 0 };
  monitorinfo.cbSize = sizeof(monitorinfo);
  GetMonitorInfo(hmonPrimary, &monitorinfo);

  // center the splash screen in the middle of the primary work area
  const RECT & rcWork = monitorinfo.rcWork;
  POINT ptOrigin;
  ptOrigin.x = 0;
  ptOrigin.y = rcWork.top + (rcWork.bottom - rcWork.top - sizeSplash.cy) / 2;

  // create a memory DC holding the splash bitmap
  HDC hdcScreen = GetDC(NULL);
  HDC hdcMem = CreateCompatibleDC(hdcScreen);
  HBITMAP hbmpOld = (HBITMAP) SelectObject(hdcMem, hbmpSplash);

  // use the source image's alpha channel for blending
  BLENDFUNCTION blend = { 0 };
  blend.BlendOp = AC_SRC_OVER;
  blend.SourceConstantAlpha = 255;
  blend.AlphaFormat = AC_SRC_ALPHA;

  // paint the window (in the right location) with the alpha-blended bitmap
  UpdateLayeredWindow(hwndSplash, hdcScreen, &ptOrigin, &sizeSplash,
      hdcMem, &ptZero, RGB(0, 0, 0), &blend, ULW_ALPHA);

  // delete temporary objects
  SelectObject(hdcMem, hbmpOld);
  DeleteDC(hdcMem);
  ReleaseDC(NULL, hdcScreen);
}

這篇關于在 C++ Win32 中創建透明窗口的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！