Text frame border radius

Based on http://musescore.org/en/node/25519#comment-100004, I decided to open a thread. I think things are pretty clear at this point, but I have long wondered, would it not be preferable to have the border radius parameter *not* be interpreted relative to the size of the frame? I find it very non-intuitive and annoying that a given border radius setting looks OK for single-letter rehearsal marks - square with slightly rounded corners - but the corners get more and more rounded the longer the text is (that's the 1.3 and current 2.0 behavior). This scaling looks strange for one-line texts, although admittedly it seems about right for larger multi-line text blocks. See below.

There is a good news / bad news solution to this. The QT function that draws the frame - drawRoundRect - has been deprecated and is now obsolete. The replacement function drawRoundedRect actually works the way I would prefer by default: a specified radius has the same effect on the corners regardless of the size of the rectangle. That's the good news. The bad news is that the units seem to work very differently in the case of relatively small rectangles at least. A "border radius" setting of 20 looked good for rehearsal marks with drawRoundRect, but that's entirely too large and produces results that look more like a circle with drawRoundedRect. On the other hand, for a larger text, drawRoundRect would have produced correspondingly more rounded corners, and actually a setting of 20 matches matches pretty well for sufficiently long texts.

So I have a proposal:

drawRoundedRect has an optional parameter that allows it to emulate the old (radius interpreted relative to frame size) behavior. We could add a new checkbox to the text style dialog to control this. I might suggest we have it default to "on" for 1.3 scores, "off" for new scores.

I realize it's hard to picture what I mean, so here are some examples:

drawRoundRect, border radius 20 (current default for rehearsal marks):

I have always been bothered by how different the first two examples look - same radius setting, very different results. The third text actually doesn't bother me.

drawRoundedRect, border radius 20 (simply replacing the obsolete function call):

Here, the value of 20 is too large for the first two texts, but perhaps isn't that bad for the last, which somehow looks good with the more rounded corners.

drawRoundedRect, border radius 5 (my subjective pick for a new default border radius):

I think this should be the default, and if people want larger boxes to have more rounded corners, they can either turn on the radius scaling option or just choose a larger border radius.

There also seems to be something wrong with the size calculation; not sure if that's a QT issue or something MuseScore needs to do to account for the change in rounding.