[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, 15 insertions, 12 deletions

diff --git a/src/mbgl/renderer/render_tile.cpp b/src/mbgl/renderer/render_tile.cpp
index 59c3ea076b..7e7e3e6d23 100644
--- a/src/mbgl/renderer/render_tile.cpp
+++ b/src/mbgl/renderer/render_tile.cpp
@@ -2,6 +2,7 @@
 #include <mbgl/renderer/painter.hpp>
 #include <mbgl/map/transform_state.hpp>
 #include <mbgl/tile/tile.hpp>
+#include <mbgl/util/math.hpp>
 
 namespace mbgl {
 
@@ -10,24 +11,26 @@ using namespace style;
 mat4 RenderTile::translateVtxMatrix(const mat4& tileMatrix,
                                     const std::array<float, 2>& translation,
                                     TranslateAnchorType anchor,
-                                    const TransformState& state) const {
+                                    const TransformState& state,
+                                    const bool inViewportPixelUnits) const {
     if (translation[0] == 0 && translation[1] == 0) {
         return tileMatrix;
     }
 
     mat4 vtxMatrix;
 
-    if (anchor == TranslateAnchorType::Viewport) {
-        const double sin_a = std::sin(-state.getAngle());
-        const double cos_a = std::cos(-state.getAngle());
-        matrix::translate(vtxMatrix, tileMatrix,
-                          id.pixelsToTileUnits(translation[0] * cos_a - translation[1] * sin_a, state.getZoom()),
-                          id.pixelsToTileUnits(translation[0] * sin_a + translation[1] * cos_a, state.getZoom()),
-                          0);
+    const float angle = inViewportPixelUnits ?
+        (anchor == TranslateAnchorType::Map ? state.getAngle() : 0) :
+        (anchor == TranslateAnchorType::Viewport ? -state.getAngle() : 0);
+
+    Point<float> translate = util::rotate(Point<float>{ translation[0], translation[1] }, angle);
+
+    if (inViewportPixelUnits) {
+        matrix::translate(vtxMatrix, tileMatrix, translate.x, translate.y, 0);
     } else {
         matrix::translate(vtxMatrix, tileMatrix,
-                          id.pixelsToTileUnits(translation[0], state.getZoom()),
-                          id.pixelsToTileUnits(translation[1], state.getZoom()),
+                          id.pixelsToTileUnits(translate.x, state.getZoom()),
+                          id.pixelsToTileUnits(translate.y, state.getZoom()),
                           0);
     }
 
@@ -37,13 +40,13 @@ mat4 RenderTile::translateVtxMatrix(const mat4& tileMatrix,
 mat4 RenderTile::translatedMatrix(const std::array<float, 2>& translation,
                                   TranslateAnchorType anchor,
                                   const TransformState& state) const {
-    return translateVtxMatrix(matrix, translation, anchor, state);
+    return translateVtxMatrix(matrix, translation, anchor, state, false);
 }
 
 mat4 RenderTile::translatedClipMatrix(const std::array<float, 2>& translation,
                                       TranslateAnchorType anchor,
                                       const TransformState& state) const {
-    return translateVtxMatrix(nearClippedMatrix, translation, anchor, state);
+    return translateVtxMatrix(nearClippedMatrix, translation, anchor, state, false);
 }
 
 void RenderTile::startRender(Painter& painter) {