On Wed, Mar 21, 2012 at 11:53 AM, <[email protected]> wrote:
> i) Implement a subset of CSS3PagedMedia to set the margin (at least the > case = 0 to hide all the header/footer) and the page size. > ii) Implement a new callback on the canvas element that is called during > the actual printing to print directly to the printing backend. > > What's the best way to get the implementation going? > > For i), there seems to be a bug already: > https://bugzilla.mozilla.org/show_bug.cgi?id=115199 > > I tried to understand what the patches are doing and couldn't figure it > out for most parts. For i), is the way to implement this by continue > working on bug 115199, or should there be a new bug that tries to implement > only a very dump subset of the CSS3PagedMedia, such that one can set the > margin to 0 and the page-size and that's it? > I think starting with the patch there is the way to go. You'll need to add code to nsSimplePageSequenceFrame::Reflow to set up margins using the style data from a (the first) nsPageFrame child. From my intuition, the second part ii) might be "easier" to implement then > the first part, as it is more contained and doesn't require to deal with > new CSS rules. I'm therefore wondering if you think this is something I > could try to implement. > > So far I have some basic understanding about how the printing stuff works, > how the CanvasReneringContext is defined in the IDL and cpp file etc. Could > someone give me some pointers where the actual printing of a canvas element > to the printing context happens, such that I could try to implement the > proposed callback? > Basically we just render the canvas like normal, but we're rendering it to a print context. What I think you need to do is: -- in nsHTMLCanvasElement::CopyInnerTo in the IsStaticDocument case, set up a reference from the cloned-for-print canvas to the original canvas -- in nsSimplePageSequenceFrame::PrintNextPage, before you render the page via nsLayoutUtils::PaintFrame, traverse the child page frame's frame subtree (see FrameChildListIterator and its users) looking for nsHTMLCanvasFrames (via do_QueryFrame). For each one, look up the original canvas, see if it has an "onprint" (or whatever we call it) event handler set on it. For those that do: -- Poke the printed nsHTMLCanvasElement's 2D rendering context (nsCanvasRenderingContext2D for now) to tell it to change its surface to a new surface created via renderingContext->GetThebes()->CurrentSurface()->CreateSimilarSurface() -- Synchronously dispatch the "print" event to the original canvas. -- That event should use a custom DOM event class (see for example nsDOMNotifyPaintEvent) with an extra field that's the 2D rendering context for the printed nsHTMLCanvasElement -- To save memory, after calling PaintFrame for the page, go back through the canvases where you fired the callbacks and clear out their surfaces. If you're really lucky, that will be enough for printing :-). For print preview: -- Add an mIsReadyToPrint flag on nsHTMLCanvasElement, initially false, -- Add an IsReadyToPrint() method on nsPageFrame that scans the frame subtree (see FrameChildListIterator) looking for nsHTMLCanvasFrames (via do_QueryFrame). If any such canvases have their mIsReadyToPrint flag not set, and the original canvas has an "onprint" callback, the page is not ready to print. -- When painting an nsPageFrame in print preview, if !IsReadyToPrint(), for each not-ready print canvas, clear out its surface and fire an asynchronous event that dispatches a "print" event to the original canvas, passing the 2D rendering context for the print canvas's context, and when that event has finished set the mIsReadyToPrint flag on the print canvas. -- To save memory, periodically check for pages that are offscreen and clear out the surfaces for the print canvases in them. At some point, hopefully soon, nsCanvasRenderingContext2D will go away and you'll need to make these changes to nsCanvasRenderingContext2DAzure instead. Rob -- “You have heard that it was said, ‘Love your neighbor and hate your enemy.’ But I tell you, love your enemies and pray for those who persecute you, that you may be children of your Father in heaven. ... If you love those who love you, what reward will you get? Are not even the tax collectors doing that? And if you greet only your own people, what are you doing more than others?" [Matthew 5:43-47] _______________________________________________ dev-tech-layout mailing list [email protected] https://lists.mozilla.org/listinfo/dev-tech-layout
