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## Re: Better pure heights for slurs (issue 5431065)

 From: mike Subject: Re: Better pure heights for slurs (issue 5431065) Date: Thu, 24 Nov 2011 21:01:34 -0800 User-agent: Roundcube Webmail/0.5.2

```On Thu, 24 Nov 2011 19:16:46 +0000, address@hidden wrote:
```
```I like the direction of this change.
```
```
Does it actually work?

```
```The code has your trademark incomprehensibility,
```
```
```
Thank you, Keith. You know, sometimes, people think that it comes naturally to be so incomprehensible, but it's actually hard work. Usually, before writing LilyPond code, I'll read a passage from either Finnegans Wake or Waiting for Godot and then recite some Gertrude Stein poetry. It helps me get my head in the right place. Of course, one likes to believe that one can always find room for improvement, but I actually think that I hit my zenith with one of my first commits via path-min-max in stencil.scm. The US government is working on its inverse function in hopes that it will help decrypt Chinese telegrams.
```
```
```so I don't know if it
```
does what you want based on your introduction. Maybe just decide that
```you want what it does.
```
```
```
It basically finds a horrendous approximation for the slope of the slur and then ret holds the y component of this height. I could have used arctans, but I decided to solve for y using the Pythagorian theorem instead. The only danger is that my estimate of the slope is likely too steep in most cases (thus yielding a smaller height than desirable), but this is offset by the fact that the height is tacked onto the highest point of the slur.
```
```
```
http://codereview.appspot.com/5431065/diff/1/lily/slur.cc
File lily/slur.cc (right):

http://codereview.appspot.com/5431065/diff/1/lily/slur.cc#newcode102
lily/slur.cc:102: height *= 0.5;
Not too harmful here, but in general redefining variables with
```
meaningful names causes other programmers to scan lines 77 through 101 for use of the original height, and then lines 103 through 118 for the new use of height, to try to determine why it changed halfway through.
```
If the conceptual "height" didn't change, just leave 'height' alone.

```
Oh, the concept is actually "height-limit". Maybe the original variable
```name wasn't perfect.  Since ret.length() is also an estimate of the
actual height of the slur, I'd take the time to change the variable
names.
```
```
Doable.

```
```http://codereview.appspot.com/5431065/diff/1/lily/slur.cc#newcode107
lily/slur.cc:107: between two columns
Trop de mots,
und ein, dass ich nicht in meinem Wörterbuch gefunden haben.

http://codereview.appspot.com/5431065/diff/1/lily/slur.cc#newcode115
```
lily/slur.cc:115: ret[dir] += dir * (sqrt (height * height / ((s * s) +
```1)) + 0.5);
Reduces to abs(0.5*height_limit) / sqrt(s²+1).
Simplifying the math, it looks like the result is nearly this:
Real encompassing_height = max(1.0, ret.length());
// Coarse estimate of how far the slur will bow upwards
ret[dir] += dir * no_elts * height_limit / encompassing_height;
ret += 0.5 * dir;
```
```
```
Yup - this'll come in slightly larger than the result in the patch, but still smaller than the original estimate. I can use it instead.
```
Cheers,
MS

```

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