Skins :: fix CPU usage & end-of-track warning when waveforms are hidden/collapsed

[ronso0]

This fixes lp:1746475 "CPU usage doubles when hiding waveforms" in Deere & LateNight
and lp:1746110 "No end of track warning if Waveform Display not enabled" in Tango

Symptoms reported in lp:1748170 "Log file grows rapidly", log file is spammed with these entries:

Warning [Main]: QPainter::begin: Paint device returned engine == 0, type: 3
Warning [Main]: QPainter::setRenderHint: Painter must be active to set rendering hints
Warning [Main]: QPainter::setMatrixEnabled: Painter not active
Warning [Main]: QPainter::setPen: Painter not active
Warning [Main]: QPainter::setBrush: Painter not active
Warning [Main]: QPainter::setBrush: Painter not active
Warning [Main]: QPainter::setFont: Painter not active
Warning [Main]: QPainter::setPen: Painter not active
Warning [Main]: QPainter::begin: Paint device returned engine == 0, type: 3
Warning [Main]: QPainter::setRenderHint: Painter must be active to set rendering hints

Deere > CPU

set minimum container height in waveforms/decks Splitter to 4px. this has no effect in skin but is apparently sufficient to keep CPU usage constant

LateNight > CPU

load waveforms as Singleton, set minimum container height in waveforms/decks Splitter to 40px

Tango > end-of-track warning

load waveforms as Singleton and place it below decks with zero height if top waveforms are hidden

[daschuer]

LGTM, Thank you.

[MK-42]

I'm having strange symptoms since this is merged on my setup - not really knowing what is causing this behaviour.
In Tango and Deree, using the GL/GLSL mode for the scrolling waveform the whole framerate of mixxx drops to 1 fps as soon as the scrolling waveforms are hidden. If I show them, everything is running smoothly on ~30fps. As soon as they are hidden again, framerate drops and whole UI, including tooltips, menu and stuff is only rendered at ~1fps (also reported by the debug output in the waveform settings). Switching waveform type to non-GL types instantly 'revives' the UI.

I'm on arch linux, 4.15.1-2
Running Gnome 3.26.2, under X currently, will test with wayland later today.

Some investigation brought glfw/glfw#680 to my attention, could it be, that GL stops rendering the offscreen-buffer and some internal timers in the gui/skin are expecting refreshes via GL-events? I remember some discussion about gui-blinking and stuff depending on waveform rendering?

Edit: that behaviour is not only limited to mixxx. If I move the glxgears demo window offscreen, so that only the header of the window is visible, the reported framrate of that window also drops to 1fps. But I think mixxx should cope with the not-that-often-rendered, invisible waveform somehow and the rest of the gui should remain responsive.

[ronso0]

@MK-42 please file this issue at launchpad so it can be tracked.
Is anything waveform related spamming your log file? If not I can mark lp:1748170 fixed

[MK-42]

Logfile spamming is fixed. Ok, will report this on launchpad

[ronso0]

@MK-42 I tried a hack in Deere and another one in Tango.
Test skins are attached to lp1758660 "GUI lag with hidden waveforms in Tango & Deere, using integrated Intel graphics". Please test if the GUI is still lagging with those.