[core] improve legibility of labels that follow lines

port https://github.com/mapbox/mapbox-gl-js/pull/4781

This improves legibility of labels that follow lines in pitched views.
The previous approach used the limited information in the shader to
calculate put the glyph in approximatelyright place. The new approach
does this more accurately by doing it on the cpu where we have access to
the entire line geometry.

1 files changed, 14 insertions, 9 deletions

diff --git a/src/mbgl/layout/symbol_instance.cpp b/src/mbgl/layout/symbol_instance.cpp
index ffb70c7ca2..02fb800df6 100644
--- a/src/mbgl/layout/symbol_instance.cpp
+++ b/src/mbgl/layout/symbol_instance.cpp
@@ -5,8 +5,8 @@ namespace mbgl {
 
 using namespace style;
 
-SymbolInstance::SymbolInstance(Anchor& anchor,
-                               const GeometryCoordinates& line,
+SymbolInstance::SymbolInstance(Anchor& anchor_,
+                               GeometryCoordinates line_,
                                const std::pair<Shaping, Shaping>& shapedTextOrientations,
                                optional<PositionedIcon> shapedIcon,
                                const SymbolLayoutProperties::Evaluated& layout,
@@ -16,33 +16,38 @@ SymbolInstance::SymbolInstance(Anchor& anchor,
                                const float textBoxScale,
                                const float textPadding,
                                const SymbolPlacementType textPlacement,
+                               const std::array<float, 2> textOffset_,
                                const float iconBoxScale,
                                const float iconPadding,
                                const SymbolPlacementType iconPlacement,
+                               const std::array<float, 2> iconOffset_,
                                const GlyphPositionMap& positions,
                                const IndexedSubfeature& indexedFeature,
                                const std::size_t featureIndex_) :
-    point(anchor.point),
+    anchor(anchor_),
+    line(line_),
     index(index_),
     hasText(shapedTextOrientations.first || shapedTextOrientations.second),
     hasIcon(shapedIcon),
 
     // Create the collision features that will be used to check whether this symbol instance can be placed
-    textCollisionFeature(line, anchor, shapedTextOrientations.second ?: shapedTextOrientations.first, textBoxScale, textPadding, textPlacement, indexedFeature),
-    iconCollisionFeature(line, anchor, shapedIcon, iconBoxScale, iconPadding, iconPlacement, indexedFeature),
-    featureIndex(featureIndex_) {
+    textCollisionFeature(line_, anchor, shapedTextOrientations.second ?: shapedTextOrientations.first, textBoxScale, textPadding, textPlacement, indexedFeature),
+    iconCollisionFeature(line_, anchor, shapedIcon, iconBoxScale, iconPadding, iconPlacement, indexedFeature),
+    featureIndex(featureIndex_),
+    textOffset(textOffset_),
+    iconOffset(iconOffset_) {
 
     // Create the quads used for rendering the icon and glyphs.
     if (addToBuffers) {
         if (shapedIcon) {
-            iconQuad = getIconQuad(anchor, *shapedIcon, line, layout, layoutTextSize, iconPlacement, shapedTextOrientations.first);
+            iconQuad = getIconQuad(*shapedIcon, layout, layoutTextSize, shapedTextOrientations.first);
         }
         if (shapedTextOrientations.first) {
-            auto quads = getGlyphQuads(anchor, shapedTextOrientations.first, textBoxScale, line, layout, textPlacement, positions);
+            auto quads = getGlyphQuads(shapedTextOrientations.first, layout, textPlacement, positions);
             glyphQuads.insert(glyphQuads.end(), quads.begin(), quads.end());
         }
         if (shapedTextOrientations.second) {
-            auto quads = getGlyphQuads(anchor, shapedTextOrientations.second, textBoxScale, line, layout, textPlacement, positions);
+            auto quads = getGlyphQuads(shapedTextOrientations.second, layout, textPlacement, positions);
             glyphQuads.insert(glyphQuads.end(), quads.begin(), quads.end());
         }
     }