MFC，在内存上下文中绘制文本(打印)

Question

我遇到了一个问题-我需要在内存中创建一个位图，在其中绘制一些文本并将其保存为BMP文件，然后用物理打印机打印出位图。我可以在对话框窗口上下文中绘制这幅画，效果很好。但当我尝试在打印机上下文中绘制相同的图形时，文本不会出现。我真的不明白为什么会这样。请帮帮我，伙计们。提前谢谢。这是代码：

void CMy2Dlg::OnButton1() 
{
// TODO: Add your control notification handler code here
CPrintDialog pd(false); 
if (pd.DoModal()==IDOK) 
{
CDC PrintDC;    
HDC hdc = pd.CreatePrinterDC();
PrintDC.Attach(hdc);    
DOCINFO infStru;                    
::ZeroMemory (&infStru, sizeof (DOCINFO));
CString title="Print test";
infStru.cbSize = sizeof (DOCINFO);      
infStru.lpszDocName=title;
infStru.lpszOutput=NULL;

PrintDC.StartDoc(&infStru);     
PrintDC.StartPage();
{           
CRect r, r2;
CBitmap memBMP, * pOldBitmap;
CPaintDC dc(this); 
CDC memDC, *pDC = &memDC;
CFont font, * pOldFont;
int width = 2000;
int height = 1500;
int textwidth = 300;
int textheight = 150;
int oldMapMode = 0;
int oldbkmode = 0;
int i, j;
LOGFONT logFont, lf;
COLORREF oldTextColor;
memset(&logFont, 0, sizeof(logFont));
logFont.lfHeight = 16;
logFont.lfWidth = 0; 
logFont.lfEscapement = 0;
logFont.lfOrientation = 0;
logFont.lfWeight = FW_NORMAL; 
logFont.lfItalic = FALSE; 
logFont.lfUnderline = FALSE; 
logFont.lfStrikeOut = 0; 
logFont.lfCharSet = ANSI_CHARSET; 
logFont.lfOutPrecision = OUT_DEFAULT_PRECIS; 
logFont.lfClipPrecision = CLIP_DEFAULT_PRECIS; 
logFont.lfQuality = DEFAULT_QUALITY; 
logFont.lfPitchAndFamily = DEFAULT_PITCH | FF_SWISS; 
strcpy(logFont.lfFaceName, "Arial");
if(memDC.CreateCompatibleDC(&PrintDC)) {
if (memBMP.CreateCompatibleBitmap(&PrintDC, width, height)) {
pOldBitmap = pDC->SelectObject(&memBMP);
pDC->FillSolidRect(0, 0, width, height, RGB(200, 200, 200));
oldTextColor = pDC->SetTextColor(RGB(255,0,0));
oldMapMode = pDC->SetMapMode(MM_LOMETRIC);
oldbkmode = pDC->SetBkMode(TRANSPARENT);

lf = logFont;
lf.lfHeight = -MulDiv(lf.lfHeight, GetDeviceCaps(pDC->GetSafeHdc(), LOGPIXELSY), 72);
//lf.lfHeight = 100;
font.CreateFontIndirect(&lf);
pOldFont = pDC->SelectObject(&font);

r.left = 10;
r.top = 10;
r.right = r.left + textwidth;
r.bottom = r.top + textheight;
r.top *= -1;
r.bottom *= -1;
pDC->MoveTo(r.left,  r.top);
pDC->LineTo(r.right, r.top);
pDC->LineTo(r.right, r.bottom);
pDC->LineTo(r.left,  r.bottom);
pDC->LineTo(r.left,  r.top);
pDC->DrawText("qwerty", &r, DT_CENTER | DT_SINGLELINE | DT_VCENTER);                    
pDC->SetMapMode(oldMapMode);
pDC->SetTextColor(oldTextColor);
pDC->SetBkMode(oldbkmode);
PrintDC.BitBlt(10, 10, width, height, pDC, 0, 0, SRCCOPY);                  
pDC->SelectObject(pOldBitmap);
pDC->SelectObject(pOldFont);                    
font.DeleteObject();
memBMP.DeleteObject();
pDC->DeleteDC();
}
}
}
PrintDC.EndPage();
PrintDC.EndDoc();
PrintDC.Detach();       
DeleteDC(hdc);
}
}

Answer 1

如果在内存DC上使用SetMapMode(MM_LOMETRIC)，则在使用BitBlt复制到打印机/显示器DC时，必须倒置绘制内存DC。宽度/高度也必须进行调整。只需使用默认映射模式(MM_TEXT(。在打印机DC上绘制时，如果需要特定的测量单位，请使用SetMapMode(MM_LOMETRIC)。

void CMy2Dlg::OnButton1() 
{
//create the bitmap
int w = 600, h = 400;
CClientDC dc(this);
CBitmap bmp;
CDC memdc;
memdc.CreateCompatibleDC(&dc);
bmp.CreateCompatibleBitmap(&dc, w, h);
auto oldbmp = memdc.SelectObject(bmp);
//draw on bitmap
memdc.FillSolidRect(0, 0, w, h, RGB(200, 200, 200));
memdc.SetTextColor(RGB(255, 0, 0));
CRect rc(0, 0, w, h);
memdc.DrawText(L"qwerty", &rc, 0);
dc.BitBlt(0, 0, w, h, &memdc, 0, 0, SRCCOPY);//optional: draw the bitmap on dialog
CPrintDialog pd(false);
if(pd.DoModal() == IDOK)
{
CDC PrintDC;
HDC hdc = pd.GetPrinterDC();
PrintDC.Attach(hdc);
DOCINFO docinfo = { sizeof(docinfo) };
docinfo.lpszDocName = L"Print test";
PrintDC.StartDoc(&docinfo);
PrintDC.StartPage();
PrintDC.BitBlt(0, 0, w, h, &memdc, 0, 0, SRCCOPY);
PrintDC.EndPage();
PrintDC.EndDoc();
}
dc.SelectObject(oldbmp);
}