Tunnels are too prominent

[westnordost]

Tunnels are too prominent, too solid.
Only the outline of the tunnel should be shown half-transparent and dashed, but the line should not be filled - or if filled, with something along the lines like 90% transparency.
Also, the outlines of normal roads and those of tunnels are merged, this looks quite weird.

[ENT8R]

The problem is that I have absolutely no idea how to show only the outline but not the whole tunnel because the tunnel will always be drawn by default...

[westnordost]

Draw it with 100% transparency?

[ENT8R]

Adding

tunnel:
  filter: { is_tunnel: true }
  draw:
    lines:
      color: [0, 0, 0, 0]
      outline:
        dash: [0.6,0.4]
        color: [0.000, 0.000, 0.000, 1.00]
        order: 400
        width: function () { return 1*4 * Math.log($zoom); }

results in

[westnordost]

Don't use the "opaque" (default) draw mode for translucent stuff. Try inlay.

[ENT8R]

Looks still like this:

[westnordost]

How about other blend modes?

[ENT8R]

The same result...

[ENT8R]

There is not even a visible effect when switching the modes...

[westnordost]

Perhaps then disable rendering tunnels again for now. There is a rat-tail attached to that feature. I.e. look at Bonn Central Station:

[ENT8R]

Alright.

[westnordost]

Okay, the goal is to make the line fill of tunnels half-transparent or even fully-transparent+preserving the line outline.

I also had a go but did not succeed. I think why the translucent blend mode does not seem to work on tunnels is because the parent rule already defines a (white) color for the road. The half-transparent white of tunnels then just adds to the white of the road.

I tried to not define the road color in the parent draw rule (for roads) but in a rule like this:

        non-tunnel:
            filter: { not: { is_tunnel: true }}
            draw:
                lines:
                    color: global.road_color

(to achieve the line for tunnels not being filled but just the outline drawn)
that works insofar as this works for all other roads that are not tunnels. However, tunnels are not drawn at all this way - the road-outline rule further below does not draw. Perhaps because in tangram-es, if no color for the line fill is specified, also the outline is not drawn.

Adding

        tunnel:
            filter: { is_tunnel: true }
            draw:
                tunnel-way:
                    color: rgba(255,0,255,0.5)

styles:
    tunnel-way:
        base: lines
        blend: translucent
        blend_order: 1

does draw tunnels (for testing: pink), but not translucent but opaque.

@matteblair, do you know what I am doing wrong? My goal is to draw tunnels with a (half-)transparent fill (while keeping the outline at full opaqueness, if possible). Though, I am failing to draw the tunnels half-transparent in the first place.
Roads style

[matteblair]

I think what's going to work best here is a lines style using the translucent blend mode:

styles:
    tunnel-style:
        base: lines
        blend: translucent

Paired with draw rules that set a low (or zero) fill opacity and a high outline opacity:

layers:
    roads:
        data: { source: nextzen}
        filter: { not: { kind: [rail, ferry] } }
        tunnel:
            filter: {is_tunnel: true }
            draw:
                lines:
                    style: tunnel-style
                    color: [0., 1., 0., 0.1]
                    width: 7px
                    order: 6
                    outline:
                        color: [.8, .8, .8, 1.]
                        width: 3px

Let me know if that looks better!

[westnordost]

Oh right, I tried your suggestion, and it looks pretty good now. I think what I did wrong was to write

        tunnel:
            filter: { is_tunnel: true }
            draw:
                tunnel-way:
                    color: rgba(255,0,255,0.5)

instead of

        tunnel:
            filter: { is_tunnel: true }
            draw:
               lines:
                    style: tunnel-way
                    color: rgba(255,0,255,0.5)

Thank you, @matteblair !