Re: [patch] several possible crashes due to invalid paragraph metrics

[Stefan Schimanski]

Another possibility of course (which I proposed somewhere in the other thread about the backspace case of Dov) is so redo the metrics of the current paragraph before setting the current font again. But then I guess they are computed twice, also during the paragraph update later.

Stefan

Am 02.06.2007 um 18:13 schrieb Stefan Schimanski:

Hi!

In http://bugzilla.lyx.org/show_bug.cgi?id=3790 a bug is reported that LyX crashes when deleting a display math at the end of a paragraph. In fact the same bug can also be triggered by backspace, enter to rebreak the paragraph and probably many more ways.

The easy fix for all that is this one:

Index: src/Bidi.cpp
===================================================================
--- src/Bidi.cpp        (Revision 18631)
+++ src/Bidi.cpp        (Arbeitskopie)
@@ -66,8 +66,11 @@
        }
        start_ = row.pos();
-       end_ = row.endpos() - 1;
-
+       

+       // before the paragraph was changed (e.g. by backspace)
+       end_ = std::min(par.size(), row.endpos()) - 1;
+       
        if (start_ > end_) {
                start_ = -1;
                return;







Stefan

The reason is that Text::setCursor (which is often called after some user action on the text to update the cursor to the new position) tries to set the current font by Text::setCurrentFont. For this the correct paragraph metrics are needed and the RTL/LTR status of the char behind or in front of the cursor. The latter triggers a Bidi::computeTables call which goes through the current line of the paragraph and sets the RTL value correctly. But for that is depends on the Row object which is only valid if the paragraph metrics are valid. The crashes which can easily be triggered with RC1, come from the Bidi::computeTables which uses that Row::endpos() information to know the end of the row. But after actions like backspace this value is wrong, hence invalid accesses are the consequence. + // possibly the row metrics are outdated and the endpos() was computed The paragraph knows the right size all the time because it is what the action handlers (e.g. for backspace) modify. In fact a clean solution would look differently IMO. Text::setCursor should not update the font at all, but trigger some kind of update (via the the Cursor's UpdateFlags) which then, after the new paragraph metrics are calculated, sets the font at the cursors position. Not sure though if this is something for intra- RC1-RC2 patches. Any opinions? The crashes I encountered up to now can all be fixed the upper patch. So I suggest to put that in for now.

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