[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, 5 insertions, 9 deletions

diff --git a/src/mbgl/text/shaping.cpp b/src/mbgl/text/shaping.cpp
index 338abe2e43..c81f25d4eb 100644
--- a/src/mbgl/text/shaping.cpp
+++ b/src/mbgl/text/shaping.cpp
@@ -27,12 +27,9 @@ void align(Shaping& shaping,
            const float verticalAlign,
            const float maxLineLength,
            const float lineHeight,
-           const std::size_t lineCount,
-           const Point<float>& translate) {
-    const float shiftX =
-    (justify - horizontalAlign) * maxLineLength + ::round(translate.x);
-    const float shiftY =
-    (-verticalAlign * lineCount + 0.5) * lineHeight + ::round(translate.y);
+           const std::size_t lineCount) {
+    const float shiftX = (justify - horizontalAlign) * maxLineLength;
+    const float shiftY = (-verticalAlign * lineCount + 0.5) * lineHeight;
     
     for (auto& glyph : shaping.positionedGlyphs) {
         glyph.x += shiftX;
@@ -205,7 +202,6 @@ void shapeLines(Shaping& shaping,
                           const float horizontalAlign,
                           const float verticalAlign,
                           const float justify,
-                          const Point<float>& translate,
                           const float verticalHeight,
                           const WritingModeType writingMode,
                           const Glyphs& glyphs) {
@@ -259,7 +255,7 @@ void shapeLines(Shaping& shaping,
     }
     
     align(shaping, justify, horizontalAlign, verticalAlign, maxLineLength, lineHeight,
-          lines.size(), translate);
+          lines.size());
     const uint32_t height = lines.size() * lineHeight;
     
     // Calculate the bounding box
@@ -288,7 +284,7 @@ const Shaping getShaping(const std::u16string& logicalInput,
                      determineLineBreaks(logicalInput, spacing, maxWidth, writingMode, glyphs));
     
     shapeLines(shaping, reorderedLines, spacing, lineHeight, horizontalAlign, verticalAlign,
-               justify, translate, verticalHeight, writingMode, glyphs);
+               justify, verticalHeight, writingMode, glyphs);
     
     return shaping;
 }