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

From: Joe Neeman
Subject: Re: Gets vertical skylines from grob stencils (issue 5626052)
Date: Mon, 20 Feb 2012 03:12:54 -0800

On Mon, Feb 20, 2012 at 12:07 AM, address@hidden <address@hidden> wrote:

On Feb 20, 2012, at 1:58 AM, Joe Neeman wrote:

> I think you're going about things in the wrong order. I think that the first goal should be to make the code clear and correct. (In fact, if your code were "done" but slow, you could push it to master but with skylining disabled for most grobs by default. That way, people could test it and give feedback. They could even enable skylining on more grobs if they didn't mind the performance hit.)

This idea was kicked around the list in various vicissitudes, but it seemed that the majority of people favored LilyPond making the best result possible out of the box.

That's fine, but it doesn't mean that it has to be that way when you first push it to master. It's up to you, of course, but I prefer not to keep my own branches unsynced from master for a long time...

> Then you should profile and benchmark it to figure out which parts need to be faster (use ./configure --enable-profiling). For example, do you know that making special cases for beams and key signatures actually helps?

I've only used `time' on large scores to get an idea, as with small scores it's difficult to tell.  I did a few runs again this morning and have gotten rid of the exception for key signatures (it does not help at all).  I think that beams help, but I'm honestly not even fluctuates a lot and I'm having trouble getting a clean read.  I am going to delete all of the exceptions (save slurs, which does help).

Have you profiled it? That will let you see which function(s) are adding the extra time.

> Having said that, there are two places that I can think of which *might* speed things up:
>  - you return a lot of vector<Box> in This might mean that a lot of things get copied (not sure about this -- c++11 is supposed to help here). It might speed things up if you pass around const vector<Box>& instead.

I did this.  I'm not sure if it results in better performance, but it can't hurt & looks cleaner.

>  - the skylines you generate are a lot more complicated than they need to be. For example, you approximate beams with 11 horizontal segments. If you were to implement my suggestion about turning line segments into skylines, you could represent a beam with 1 sloped segment.

This is true.  I have a test case with 1200 hairpins (12 staves, 100 hairpins a piece) and this brings the compilation time down from about 19.9' to 19.5' on average.  So there's definitely a performance increase.  The issue I'm having is figuring out a good way to implement this so that it maintains a meaningful notion of what "horizon padding" is.  For example, if two skylines are merged with different horizon paddings, do they retain the horizon paddings of the old grobs (harder to code) or take the horizon padding of the new grob (easier to code)?  Or both - do they retain the old and tack on the new?  These ideas are currently ill defined but would need to be solidified.  I'm an advocate of the horizon padding of the new grob (or prob) only ever kicking in and forgetting the previous ones, operating under the assumption that if someone wants to hardcode an earlier horizon padding upstream for a given skyline, it'd be better to tack the padding onto the boxes that make the skyline and not the skyline itself.  Thoughts?

New grob sounds good. 


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