使用EnumDisplayMonitors的屏幕保护程序仅在第二个监视器上绘制黑色矩形

问题描述

我尝试了以下代码，但除了第二个监视器上的黑色矩形(使用GDI +)外，我什么都没得到.有人听说过这个问题吗?我在第二个监视器上所做的任何绘图(位图或文本)都呈现为黑色矩形.谢谢！

I tried the following code but I am getting nothing but black rectangles where my drawing images should be (using GDI+) on my 2nd monitor. Has anyone heard of this issue? Any drawing I do (bitmap or text) on the second monitor renders as a black rectangle. Thanks!

LRESULT WINAPI ScreenSaverProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)  
{
   static UINT         uTimer;   // timer identifier

   // Handles screen saver messages  
   switch(message)  
   { 
      // <snip>
      case WM_PAINT:   //  Sent when the system or another application makes a request to paint a portion of an application's window (e.g., UpdateWindow/RedrawWindow)
      {
         PAINTSTRUCT lpPaint = {0};
         HDC hdc = BeginPaint(hwnd, &lpPaint );
            EnumDisplayMonitors(hdc, NULL, MonitorNumProcPaint, 0);  // For every monitor attached, call the passed in function
         EndPaint(hwnd, &lpPaint);
         return true;
      }
      // <snip>
   }
}
 
BOOL CALLBACK MonitorNumProcPaint(HMONITOR hMonitor, HDC hdc, LPRECT lprcMonitor, LPARAM data)
{
   // If the coordinates of the top left corner are 0,0, then we're rendering on the primary monitor, otherwise we're not.
   if (lprcMonitor->left == 0 && lprcMonitor->top == 0)
      return (PaintPrimaryDisplay(hMonitor, hdc, lprcMonitor, data));
   else
      return (PaintNonPrimaryDisplay(hMonitor, hdc, lprcMonitor, data));
}
 
bool PaintNonPrimaryDisplay(HMONITOR hMonitor, HDC hdc, LPRECT lprcMonitor, LPARAM data)
{
   Gdiplus::Graphics * pGraphics = Gdiplus::Graphics::FromHDC(hdc);
 
   if (gpBitmapMotivation2)
   {
      pGraphics->DrawImage(gpBitmapMotivation2, lprcMonitor->left, lprcMonitor->top, lprcMonitor->right - lprcMonitor->left, lprcMonitor->bottom - lprcMonitor->top);
   }
 
   int sizeX = (int) ceil( (lprcMonitor->right - lprcMonitor->left) * SS_SCREEN_PERCENTAGE);
   int sizeY = (int) ceil( (lprcMonitor->bottom- lprcMonitor->top)  * SS_SCREEN_PERCENTAGE);
   DrawMyText(lprcMonitor, sizeX, sizeY, pGraphics, "MyText"); // This custom function sets up the font, etc and renders the text.

   BitBlt(hdc, lprcMonitor->left, lprcMonitor->top, lprcMonitor->right - lprcMonitor->left, lprcMonitor->bottom - lprcMonitor->top, hdc, lprcMonitor->left, lprcMonitor->top, SRCCOPY);
 
   return true;
}

推荐答案

gHdc = BeginPaint(hwnd, &gPaintStruct);   // Get Device Context handle from canvas
   // For every monitor attached, call the passed in function
   EnumDisplayMonitors(gHdc, NULL, MonitorNumProcPaint, (LPARAM)&gHdc); 
EndPaint(hwnd, &gPaintStruct);            // Painting is done

BOOL PaintNonPrimaryDisplay(HMONITOR hMonitor, LPRECT lprcMonitor, LPARAM dwData)
{
   HDC *pdc = (HDC*)dwData;
//From http://www.realtimesoft.com/multimon/forum/messages.asp?Topic=3760&tmpl=UltraMon)

   // Create an "off screen" DC (double buffer) to avoid flickering
   HDC hdcMem = CreateCompatibleDC(*pdc);
   HBITMAP hbmMem = CreateCompatibleBitmap(*pdc, lprcMonitor->right - lprcMonitor->left, lprcMonitor->bottom - lprcMonitor->top);
   HGDIOBJ hOld = SelectObject(hdcMem, hbmMem);

   // Paint everything into the double buffer
   Gdiplus::Graphics  *gpGraphics = Gdiplus::Graphics::FromHDC(hdcMem);
   if (gpGraphics == NULL)
      return false;

   if (gpBitmapMotivations[1])
   {
      gpGraphics->DrawImage(gpBitmapMotivations[1], 0, 0, lprcMonitor->right - lprcMonitor->left, lprcMonitor->bottom - lprcMonitor->top);
   }

   DrawOverlay(0, 0, lprcMonitor->right - lprcMonitor->left, lprcMonitor->bottom - lprcMonitor->top, gpGraphics);

   // Transfer the "off screen" (double buffer) DC (Device Context) to the screen
   // BitBlt Specs: http://msdn.microsoft.com/en-us/library/dd183370(v=VS.85).aspx
   BitBlt(*pdc, lprcMonitor->left, lprcMonitor->top, lprcMonitor->right - lprcMonitor->left, lprcMonitor->bottom - lprcMonitor->top, hdcMem, 0, 0, SRCCOPY);
   
   // Free the "off screen" DC
   delete gpGraphics;
   SelectObject(hdcMem, hOld);
   DeleteObject(hbmMem);
   DeleteDC(hdcMem);

   return TRUE;
}

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