[core] Set "max_camera_distance" to 1.5 for viewport-aligned road labels.

Viewport-aligned curved labels start to look very strange in the distance. Until we have a better system for projecting them, just prevent them from showing.

src/mbgl/programs/symbol_program.cpp

@@ -61,7 +61,7 @@ Values makeValues(const bool isText,
         uniforms::u_collision_y_stretch::Value{ tile.tile.yStretch() },
         uniforms::u_camera_to_center_distance::Value{ state.getCameraToCenterDistance() },
         uniforms::u_pitch::Value{ state.getPitch() },
-        uniforms::u_max_camera_distance::Value{ 10.0f },
+        uniforms::u_max_camera_distance::Value{ values.maxCameraDistance },
         std::forward<Args>(args)...
     };
 }

src/mbgl/renderer/layers/render_symbol_layer.cpp

@@ -88,11 +88,24 @@ style::SymbolPropertyValues RenderSymbolLayer::iconPropertyValues(const style::S
             evaluated.get<style::IconTranslateAnchor>(),
             evaluated.get<style::IconHaloColor>().constantOr(Color::black()).a > 0 &&
             evaluated.get<style::IconHaloWidth>().constantOr(1),
-            evaluated.get<style::IconColor>().constantOr(Color::black()).a > 0
+            evaluated.get<style::IconColor>().constantOr(Color::black()).a > 0,
+            10.0f
     };
 }
 
 style::SymbolPropertyValues RenderSymbolLayer::textPropertyValues(const style::SymbolLayoutProperties::PossiblyEvaluated& layout_) const {
+    // We hide line labels with viewport alignment as they move into the distance
+    // because the approximations we use for drawing their glyphs get progressively worse
+    // The "1.5" here means we start hiding them when the distance from the label
+    // to the camera is 50% greater than the distance from the center of the map
+    // to the camera. Depending on viewport properties, you might expect this to filter
+    // the top third of the screen at pitch 60, and do almost nothing at pitch 45
+    // "10" is effectively infinite at any pitch we support
+    const bool limitMaxDistance =
+        layout_.get<style::SymbolPlacement>() == style::SymbolPlacementType::Line
+        && layout_.get<style::TextRotationAlignment>() == style::AlignmentType::Map
+        && layout_.get<style::TextPitchAlignment>() == style::AlignmentType::Viewport;
+
     return style::SymbolPropertyValues {
             layout_.get<style::TextPitchAlignment>(),
             layout_.get<style::TextRotationAlignment>(),
@@ -100,7 +113,8 @@ style::SymbolPropertyValues RenderSymbolLayer::textPropertyValues(const style::S
             evaluated.get<style::TextTranslateAnchor>(),
             evaluated.get<style::TextHaloColor>().constantOr(Color::black()).a > 0 &&
             evaluated.get<style::TextHaloWidth>().constantOr(1),
-            evaluated.get<style::TextColor>().constantOr(Color::black()).a > 0
+            evaluated.get<style::TextColor>().constantOr(Color::black()).a > 0,
+            limitMaxDistance ? 1.5f : 10.0f
     };
 }
 

src/mbgl/renderer/layers/render_symbol_layer.hpp

@@ -47,6 +47,8 @@ public:
 
     bool hasHalo;
     bool hasFill;
+    
+    float maxCameraDistance; // 1.5 for road labels, or 10 (essentially infinite) for everything else
 };
 
 } // namespace style