+ m_previewScaleX = float(logPPIScreenX) / logPPIPrinterX;
+ m_previewScaleY = float(logPPIScreenY) / logPPIPrinterY;
+}
+
+
+#if wxUSE_HIGH_QUALITY_PREVIEW
+
+// 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 attempt to render the preview into high-resolution bitmap
+// using DC with same resolution etc. as the printer DC. This takes lot of
+// memory, so the code is more complicated than it could be, but the results
+// are much better.
+//
+// Finally, this code is specific to wxMSW, because it doesn't make sense to
+// bother with it on other platforms. Both OSX and modern GNOME/GTK+
+// environments have builtin accurate preview (that applications should use
+// instead) and the differences between screen and printer DC in wxGTK are so
+// large than this trick doesn't help at all.
+
+namespace
+{
+
+// If there's not enough memory, we need to render the preview in parts.
+// Unfortunately we cannot simply use wxMemoryDC, because it reports its size
+// as bitmap's size, and we need to use smaller bitmap while still reporting
+// original ("correct") DC size, because printing code frequently uses
+// GetSize() to determine scaling factor. This DC class handles this.
+
+class PageFragmentDCImpl : public wxMemoryDCImpl
+{
+public:
+ PageFragmentDCImpl(wxMemoryDC *owner, wxDC *printer,
+ const wxPoint& offset,
+ const wxSize& fullSize)
+ : wxMemoryDCImpl(owner, printer),
+ m_offset(offset),
+ m_fullSize(fullSize)
+ {
+ SetDeviceOrigin(0, 0);
+ }
+
+ virtual void SetDeviceOrigin(wxCoord x, wxCoord y)
+ {
+ wxMemoryDCImpl::SetDeviceOrigin(x - m_offset.x, y - m_offset.y);
+ }
+
+ virtual void DoGetDeviceOrigin(wxCoord *x, wxCoord *y) const
+ {
+ wxMemoryDCImpl::DoGetDeviceOrigin(x, y);
+ if ( x ) *x += m_offset.x;
+ if ( x ) *y += m_offset.y;
+ }
+
+ virtual void DoGetSize(int *width, int *height) const
+ {
+ if ( width )
+ *width = m_fullSize.x;
+ if ( height )
+ *height = m_fullSize.y;
+ }
+
+private:
+ wxPoint m_offset;
+ wxSize m_fullSize;
+};
+
+class PageFragmentDC : public wxDC
+{
+public:
+ PageFragmentDC(wxDC* printer, wxBitmap& bmp,
+ const wxPoint& offset,
+ const wxSize& fullSize)
+ : wxDC(new PageFragmentDCImpl((wxMemoryDC*)this, printer, offset, fullSize))
+ {
+ static_cast<PageFragmentDCImpl*>(m_pimpl)->DoSelect(bmp);
+ }
+};
+
+// estimate how big chunks we can render, given available RAM
+long ComputeFragmentSize(long printerDepth,
+ long width,
+ long height)
+{
+ // Compute the amount of memory needed to generate the preview.
+ // Memory requirements of RenderPageFragment() are as follows:
+ //
+ // (memory DC - always)
+ // width * height * printerDepth/8
+ // (wxImage + wxDIB instance)
+ // width * height * (3 + 4)
+ // (this could be reduced to *3 if using wxGraphicsContext)
+ //
+ // So, given amount of memory M, we can render at most
+ //
+ // height = M / (width * (printerDepth/8 + F))
+ //
+ // where F is 3 or 7 depending on whether wxGraphicsContext is used or not
+
+ wxMemorySize memAvail = wxGetFreeMemory();
+ if ( memAvail == -1 )
+ {
+ // we don't know; 10meg shouldn't be a problem hopefully
+ memAvail = 10000000;
+ }
+ else
+ {
+ // limit ourselves to half of available RAM to have a margin for other
+ // apps, for our rendering code, and for miscalculations
+ memAvail /= 2;
+ }
+
+ const float perPixel = float(printerDepth)/8 + (3 + 4);
+
+ const long perLine = long(width * perPixel);
+ const long maxstep = (memAvail / perLine).GetValue();
+ const long step = wxMin(height, maxstep);
+
+ wxLogTrace("printing",
+ "using %liMB of RAM (%li lines) for preview, %li %lipx fragments",
+ long((memAvail >> 20).GetValue()),
+ maxstep,
+ (height+step-1) / step,
+ step);
+
+ return step;
projects / wxWidgets.git / blobdiff