don't permanently crossfade patterns

[ansis]

This is how patterns currently look:

z15

z15.5

z16

At fractional zooms, the pattern is permanently crossfaded. The waves in the z15.5 image aren't clear.

Would it be better to not permanently fade and just show one scale?
For comparison, z15.5 without permanent crossfading looks like this:

Whenever a zoom boundary is crossed (from 15.99 to 16) the scale resets to avoid infinitely scaling. We could use timed transitions to make those smooth.

@nickidlugash @edenh @peterqliu

[edenh]

It would be great if patterns were crossfaded the way labels are instead of making the fade relative to zoom level. For example, as soon as z > 2, start fading to the new pattern scale. If necessary, add the equivalent to raster-fade or use the global transition setting to control fade duration.

[nickidlugash]

This sounds good to me.

[peterqliu]

The one upside of zoom-based crossfading, is that any change to the pattern begins and ends with the user's explicit zooming action.

The tradeoff with using time-based fading, is a split-second of pattern shifting after the user has finished zooming. If this transition is long it'll feel like a lag; if it's short, it'll feel like a very sudden jump.

[edenh]

The tradeoff with using time-based fading, is a split-second of pattern shifting after the user has finished zooming.

Labels are faded as you hit specific zoom levels, not after.

[ansis]

I was imagining that pattern fading would occur during zoom in the current manner, but snap to the nearest scale when zoom ends.

I think this would be more distracting. What I meant was fading only during a timed transition after crossing a boundary where the scale is reset. For example:

start zooming
z13 - scale 1
z13.5 - scale ~1.5
z13.99 - scale ~1.99
z14 - start fading from scale 2 to 1
z14.5 - middle of fade from scale ~3 to 1.5
stop zooming
z14.5 - scale ~1.5 when fading ends maybe 150ms or whatever after hitting z14

[peterqliu]

@edenh explained it to me via chat as well 👍 sounds good

[jfirebaugh]

Are there spec-side changes required for this or is it purely a renderer change?

[ansis]

No spec changes necessary. Implemented:
mapbox/mapbox-gl-js#950
mapbox/mapbox-gl-native#773