Fixes several performance problems found with Valgrind

[michaelgregorius]

Removes some repeated calls to Qt's font layouting:

• FxLine::drawFxLine now uses a QStaticText instance to render the channel names. The method drawFxLine was turned into a member method so that the QStaticText member can be accessed.
• Removing the overridden method ComboBox::sizeHint.

Unifies Mixer::peakValueLeft and Mixer::peakValueRight into
Mixer::getPeakValues so the array is only iterated once.

[Fastigium]

Did a quick test, and it looks good to me 👍. Nice optimization work! Minor nitpicking: https://github.com/LMMS/lmms/pull/2579/files#diff-b6cdb0811e7a10721f0bfb60ea98f525R180 lacks the spaces between parentheses and arguments, but I believe that particular style guideline isn't observed that strictly anymore.

[tresf]

I believe that particular style guideline isn't observed that strictly anymore.

Correct. We're slowly moving away from it, so we try to do our best to match the style of the item we're modifying until we have time to clean it all up. 👍

[Wallacoloo]

Function should be const.

[Wallacoloo]

Works well. Look into marking any const methods (I left code comments), and then it should be good to merge, I'd say.

[tresf]

Hmm... Travis says this errored, but the green check is above...

Even stranger, the build actually compiled, but says exit 1. Safe to ignore I think, but we'll keep our eye on it. Re-launched the Travis process just incase.

[100%] Building CXX object tests/CMakeFiles/tests.dir/tests_automoc.cpp.o
[100%] Linking CXX executable tests
[100%] Built target tests
>> Will run 1 test suites 
********* Start testing of ProjectVersionTest *********
Config: Using QTest library 4.8.7, Qt 4.8.7
PASS   : ProjectVersionTest::initTestCase()
PASS   : ProjectVersionTest::test()
PASS   : ProjectVersionTest::cleanupTestCase()
Totals: 3 passed, 0 failed, 0 skipped
********* Finished testing of ProjectVersionTest *********
<< 0 out of 1 test suites failed. 
The command "if [[ $TARGET_OS != win* ]]; then make tests && ./tests/tests; fi;" exited with 0.
Done. Your build exited with 1.

[michaelgregorius]

@tresf That's strange indeed. I have actually waited for all builds to succeed before merging this one. Is the attached image from the relaunched build? Only asking because my build was 3510.* and 3510.4 and 3510.5 both say they exited with 0.

[tresf]

It appears there were two... the pull request and the merge... I don't know and now I have a headache...

On a side note, Travis is known to throw false warnings from time to time. 😕