Re: Drawing complex scripts with pango.

My current advice: wait until I recover the patch that totally rewrites
that ::_draw method. It will fix both issues.

But please give me a day or 2, Wendy is getting an operation tomorrow
that needs my attention.

  Marc

On Mon, 2009-08-17 at 11:24 -0400, Dominic Lachowicz wrote:
> My only advice is "talk to behdad".
>
> On Mon, Aug 17, 2009 at 3:22 AM, Martin Sevior<msevior@gmail.com> wrote:
> >
> > Hi everyone,
> > Bug 12284 nepali text selection oddities,
> >
> > http://bugzilla.abisource.com/show_bug.cgi?id=12284
> >
> > See the effect in this screenshot:
> >
> > http://bugzilla.abisource.com/attachment.cgi?id=5028
> >
> > Is caused by the same effect that makes characters "dance" around on
> > the screen as we select them.
> >
> > The problem is that pango doesn't like rendering starting from the
> > middle of a run characters. For roman text it's left-more position is
> > undefined to within one pixel. For complex scripts like Nepalese where
> > two or more unicode values are combined to make one glyph pango just
> > doesn't draw the string.
> >
> > The problem is in fp_TextRun::_draw(...)
> >
> > The problem code is this:
> >
> > // reset the iterator
> > text.setPosition(iIterPos);
> > m_pRenderInfo->m_iOffset = iMyOffset;
> > m_pRenderInfo->m_iLength =
> > iSegmentOffset[iSegment+1]-iSegmentOffset[iSegment];
> > m_pRenderInfo->m_xoff = iX;
> > m_pRenderInfo->m_yoff = yTopOfRun;
> > painter.renderChars(*m_pRenderInfo);
> >
> > and in particular setting m_pRenderInfo->m_iOffset and m_pRenderInfo->m_iLength.
> >
> > If we replace this with code with and always do one complete draw for
> > the run, rather than draw in segments
> >
> > pG->setColor(getFGColor());
> > if(iVisDir == UT_BIDI_RTL)
> > iX -= getWidth();
> > m_pRenderInfo->m_iOffset = 0;
> > m_pRenderInfo->m_iLength = getLength();
> > m_pRenderInfo->m_xoff = iX;
> > m_pRenderInfo->m_yoff = yTopOfRun;
> > painter.renderChars(*m_pRenderInfo);
> >
> > The dancing characters and fixed and we draw correctly. The downside
> > is that we always use the some color for the foreground text instead
> > of the
> > fancy color selection we currently with this code:
> >
> > if(bSegmentSelected[iSegment])
> > {
> > pG->setColor(_getView()->getColorSelForeground());
> > }
> > else
> > {
> > pG->setColor(getFGColor());
> > }
> >
> > I'm personally happy to give up the fancy color. I know that uwog
> > didn't not like to do this, but that was before this selection bug
> > showed up.
> >
> > What are peoples opinions on how to proceed? My impression is that for
> > complex scripts the output of pango is undefined if you attempt to
> > draw in the middle of a run.
> >
> > Cheers,
> >
> > Martin
> >
>
>
>
Received on Mon Aug 17 21:11:19 2009