Re: Gets vertical skylines from grob stencils (issue 5626052)

[mtsolo]

http://codereview.appspot.com/5626052/diff/85004/lily/skyline.cc
File lily/skyline.cc (right):

http://codereview.appspot.com/5626052/diff/85004/lily/skyline.cc#newcode292
lily/skyline.cc:292: Real p1 = left->end_ * left->slope_ +
left->y_intercept_;
On 2012/07/14 14:01:08, joeneeman wrote:
> use left->height (left_end_) instead of calculating it by hand

Done.

http://codereview.appspot.com/5626052/diff/85004/lily/skyline.cc#newcode293
lily/skyline.cc:293: Real p2 = i->start_ * i->slope_ + i->y_intercept_;
On 2012/07/14 14:01:08, joeneeman wrote:
> i->height (i->start_)

Done.

http://codereview.appspot.com/5626052/diff/85004/lily/skyline.cc#newcode302
lily/skyline.cc:302: while (dirty);
On 2012/07/14 14:01:08, joeneeman wrote:
> I don't understand this do while (dirty) part. It seems to me that
unless you
> have two empty segments in a row, you only need one pass. On the other
hand, if
> you have two empty segments in a row then this function will fail
anyway because
> you will end up setting center->slope_ and center->y_intercept_ both
to
> -infinity, which is bound to start creating NaN sooner or later.

I'll rewrite this so that it combines all interior skylines with an
infinite y intercept and then only does one pass.

http://codereview.appspot.com/5626052/diff/90001/lily/include/skyline.hh
File lily/include/skyline.hh (right):

http://codereview.appspot.com/5626052/diff/90001/lily/include/skyline.hh#newcode58
lily/include/skyline.hh:58: NOT_ENOUGH_INFO
On 2012/07/14 14:01:08, joeneeman wrote:
> I wish I could convince you to think of a skyline as a region instead
of just
> the boundary of that region. Once you think of it that way, it becomes
clear
> that this information can be easily obtained from the Skyline_pair,
using the
> existing distance function.

> Suppose s and t are Skyline_pairs.
> max(s[UP].distance(t[DOWN]), s[DOWN].distance(t[UP])) = -infinity
> means the objects don't overlap horizontally at all, so it's
meaningless to talk
> about which one is higher (I think this is what you're calling
NOT_ENOUGH_INFO).

> min(s[UP].distance(t[DOWN]), s[DOWN].distance(t[UP])) > 0
> means that the objects intersect.

> s[UP].distance(t[DOWN]) <= 0 and s[DOWN].distance(t[UP]) > 0
> means that s is below t

> t[UP].distance(s[DOWN]) <= 0 and t[DOWN].distance(s[UP]) > 0
> means that t is below s

This logic uses two calls to distance, which is expensive, whereas using
the e-num gets this info from one call to distance.  I can use the
method you propose, but don't you think that'd cause a performance hit?

http://codereview.appspot.com/5626052/diff/90001/lily/skyline.cc
File lily/skyline.cc (right):

http://codereview.appspot.com/5626052/diff/90001/lily/skyline.cc#newcode796
lily/skyline.cc:796: */
On 2012/07/14 14:01:08, joeneeman wrote:
> Since padding doesn't seem to be involved in this function, you should
delete
> this comment.

Done.

http://codereview.appspot.com/5626052/