The Waveform, Vectorscope and Histogram panels were black when running on
the Vulkan / backend-neutral render path because ScopeBase::OnPaint()
returned early with a TODO. The viewer emits GPU textures that live in the
viewer's own renderer; on Vulkan each ManagedDisplayWidget has a separate
device, so those textures cannot be sampled directly.
Fix by:
- Adding a backend-neutral branch in ScopeBase::OnPaint() that downloads the
reference texture (cross-renderer if needed), color-manages it into a U8
offscreen texture, downloads it to a QImage, and draws via QPainter.
- Adding a pure virtual DrawScopeSoftware() to ScopeBase and implementing it
for WaveformScope, VectorscopeScope and HistogramScope.
- Fixing the managed_tex_up_to_date_ flag that was never set to true in the
OpenGL path, which caused the color-managed scope texture to be recreated
on every paint.
All gtest suites pass.
Mike-Solar