Considerations for hi-res displays

[ejeschke]

I've recently upgraded to 4K displays, and I notice some minor issues with ginga usability that probably ought to be addressed. For example, both Qt and Gtk widget sets have a scaling option to scale most widgets "behind the scenes" by a constant factor. For example, Qt has the QT_DEVICE_PIXEL_RATIO environment variable (integers only) and Gtk has GDK_SCALE.

Happily, most of these are now also integrated into the OS desktop settings and work fairly seamlessly. But some Ginga UI elements are constructed to a fixed scale, such as the icons in the Toolbar plugin, thumb resolution, etc. We probably need to find a way to handle these more elegantly. If SVG icons are handled a little better by Qt these days that might be an option for the toolbar icons--I remember it was Qt that drove the initial decision to go with scaled PNGs.

There are a lot of possibilities, from calculations on the available desktop area to having an explicit user preference to override.

One other issue is that demands on performance of the basic image rendering is pushed into new territory. Because the image windows are not scaled, the sheer number of visible pixels is much larger in a hi-res display, putting more pressure on the rendering pipeline. Things that were perfectly snappy seem a little more sluggish as the Ginga window is enlarged on such a display. We probably need to look at something like GPU acceleration of scaling and rotation.