Highway shield text is tilted

[1ec5]

When the map is tilted, Interstate and state route shields remain upright, as expected, but the text inside them tilts with the map:

Reproduces in Streets, Outdoors, and Satellite Streets styles in 5fb0e87 on iOS and macOS. Does not reproduce in mapbox/mapbox-gl-js@742b46d:

Exit shields are unaffected. The difference is likely that highway shields have line placement, whereas exit shields have point placement.

[1ec5]

Bisect implicates ecd4aa1 (#5288).

/cc @yhahn

[yhahn]

@1ec5 sorry for the delay -- I started digging into this yesterday and need to vet what I think is a subtle difference in behavior between the way an undefined pitch alignment value is handled in the style:

• Native

  mapbox-gl-native/src/mbgl/style/layers/symbol_layer_impl.cpp

  Lines 39 to 47 in c075386

  	if (bucket->layout.symbolPlacement.value == SymbolPlacementType::Line) {
  	bucket->layout.iconRotationAlignment.value = AlignmentType::Map;
  	bucket->layout.textRotationAlignment.value = AlignmentType::Map;
  	};
  	// If unspecified `text-pitch-alignment` inherits `text-rotation-alignment`
  	if (bucket->layout.textPitchAlignment.value == AlignmentType::Undefined) {
  	bucket->layout.textPitchAlignment.value = bucket->layout.textRotationAlignment.value;
  	};

• JS https://github.com/mapbox/mapbox-gl-js/blob/5dc94794330e9ea43e5e546ceda823d312665f58/js/style/style_layer/symbol_style_layer.js#L25-L38

Will keep trying to get to the bottom of this today.

[1ec5]

Just a hunch, but in gl-native, if symbolPlacement is line, it doesn’t look like it’s possible for either iconRotationAlignment or textRotationAlignment to be viewport for the purpose of a textPitchAlignment fallback, even if the stylesheet sets it explicitly, because this line will read the value that was set here rather than the raw value specified by the style. The corresponding code in GL JS only defaults text-rotation-alignment to map if it isn’t specified in the stylesheet; likewise for icon-rotation-alignment.

[1ec5]

Indeed, falling back to a temporarily stored value of text-rotation-alignment does fix the immediate issue. Here’s what 1ec5-shields-upright-5683 looks like:

On the other hand, it isn’t quite right because the street labels are also falling back to viewport now.

Effectively, this means that text-pitch-alignment falls back to the literal value of text-rotation-alignment but not the computed value. Is this what the style specification normally means by “matching” a property?

[boundsj]

I think the following summarizes what is required to land the set of PRs that fix this issue:

• Add auto to the style spec Add an explicit enum value to the spec for text and icon pitch and rotation mapbox-gl-style-spec#493
• Better handling for undefined icon|text-rotation-alignment #6253 @ivovandongen or @zugaldia review Android commit d26c5ce
• Better handling for undefined icon|text-rotation-alignment #6253 @jfirebaugh final overall review (merging is currently blocked because no reviews)
• Land Better handling for undefined icon|text-rotation-alignment #6253
• Land [not ready] Better handling for undefined icon|text-rotation-alignment mapbox-gl-js#3203 @jfirebaugh
• Land [not ready] Add tests for text-pitch-, text-rotation-, icon-rotation-alignment auto enum mapbox-gl-test-suite#144 @jfirebaugh

In the future, the style spec should be updated to reflect the released versions that support auto where applicable.