bool wxWindowsPrintPreview::RenderPageIntoBitmap(wxBitmap& bmp, int pageNum)
{
// The preview, as implemented in wxPrintPreviewBase (and as used prior to
// wx3) is inexact: it uses screen DC, which has much lower resolution and
// has other properties different from printer DC, so the preview is not
// quite right.
//
// To make matters worse, if the application depends heavily on
// GetTextExtent() or does text layout itself, the output in preview and on
// paper can be very different. In particular, wxHtmlEasyPrinting is
// affected and the preview can be easily off by several pages.
//
// To fix this, we render the preview into high-resolution enhanced
// metafile with properties identical to the printer DC. This guarantees
// metrics correctness while still being fast.
// print the preview into a metafile:
wxPrinterDC printerDC(m_printDialogData.GetPrintData());
wxEnhMetaFileDC metaDC(printerDC,
wxEmptyString,
printerDC.GetSize().x, printerDC.GetSize().y);
if ( !RenderPageIntoDC(metaDC, pageNum) )
return false;
wxEnhMetaFile *metafile = metaDC.Close();
if ( !metafile )
return false;
// now render the metafile:
wxMemoryDC bmpDC;
bmpDC.SelectObject(bmp);
bmpDC.Clear();
wxRect outRect(0, 0, bmp.GetWidth(), bmp.GetHeight());
metafile->Play(&bmpDC, &outRect);
delete metafile;
// TODO: we should keep the metafile and reuse it when changing zoom level
return true;
}
bool wxWindowsPrintPreview::RenderPageFragment(float scaleX, float scaleY,
int *nextFinalLine,
wxPrinterDC& printer,
wxMemoryDC& finalDC,
const wxRect& rect,
int pageNum)
{
// compute 'rect' equivalent in the small final bitmap:
const wxRect smallRect(wxPoint(0, *nextFinalLine),
wxPoint(int(rect.GetRight() * scaleX),
int(rect.GetBottom() * scaleY)));
wxLogTrace("printing",
"rendering fragment of page %i: [%i,%i,%i,%i] scaled down to [%i,%i,%i,%i]",
pageNum,
rect.x, rect.y, rect.GetRight(), rect.GetBottom(),
smallRect.x, smallRect.y, smallRect.GetRight(), smallRect.GetBottom()
);
// create DC and bitmap compatible with printer DC:
wxBitmap large(rect.width, rect.height, printer);
if ( !large.IsOk() )
return false;
// render part of the page into it:
{
PageFragmentDC memoryDC(&printer, large,
rect.GetPosition(),
wxSize(m_pageWidth, m_pageHeight));
if ( !memoryDC.IsOk() )
return false;
memoryDC.Clear();
if ( !RenderPageIntoDC(memoryDC, pageNum) )
return false;
} // release bitmap from memoryDC
// now scale the rendered part down and blit it into final output:
wxImage img;
{
wxDIB dib(large);
if ( !dib.IsOk() )
return false;
large = wxNullBitmap; // free memory a.s.a.p.
img = dib.ConvertToImage();
} // free the DIB now that it's no longer needed, too
if ( !img.IsOk() )
return false;
img.Rescale(smallRect.width, smallRect.height, wxIMAGE_QUALITY_HIGH);
if ( !img.IsOk() )
return false;
wxBitmap bmp(img);
if ( !bmp.IsOk() )
return false;
img = wxNullImage;
finalDC.DrawBitmap(bmp, smallRect.x, smallRect.y);
if ( bmp.IsOk() )
{
*nextFinalLine += smallRect.height;
return true;
}
return false;
}