[core] Use indexed rendering for collision boxes

4 files changed, 33 insertions, 12 deletions

diff --git a/src/mbgl/layout/symbol_layout.cpp b/src/mbgl/layout/symbol_layout.cpp
index 932745aa57..d974e6a357 100644
--- a/src/mbgl/layout/symbol_layout.cpp
+++ b/src/mbgl/layout/symbol_layout.cpp
@@ -507,14 +507,28 @@ void SymbolLayout::addToDebugBuffers(CollisionTile& collisionTile, SymbolBucket&
                 const float maxZoom = util::clamp(zoom + util::log2(box.maxScale), util::MIN_ZOOM_F, util::MAX_ZOOM_F);
                 const float placementZoom = util::clamp(zoom + util::log2(box.placementScale), util::MIN_ZOOM_F, util::MAX_ZOOM_F);
 
-                collisionBox.vertices.emplace_back(CollisionBoxProgram::vertex(anchor, tl, maxZoom, placementZoom),
-                                                   CollisionBoxProgram::vertex(anchor, tr, maxZoom, placementZoom));
-                collisionBox.vertices.emplace_back(CollisionBoxProgram::vertex(anchor, tr, maxZoom, placementZoom),
-                                                   CollisionBoxProgram::vertex(anchor, br, maxZoom, placementZoom));
-                collisionBox.vertices.emplace_back(CollisionBoxProgram::vertex(anchor, br, maxZoom, placementZoom),
-                                                   CollisionBoxProgram::vertex(anchor, bl, maxZoom, placementZoom));
-                collisionBox.vertices.emplace_back(CollisionBoxProgram::vertex(anchor, bl, maxZoom, placementZoom),
-                                                   CollisionBoxProgram::vertex(anchor, tl, maxZoom, placementZoom));
+                static constexpr std::size_t vertexLength = 4;
+                static constexpr std::size_t indexLength = 8;
+
+                if (collisionBox.segments.empty() || collisionBox.segments.back().vertexLength + vertexLength > std::numeric_limits<uint16_t>::max()) {
+                    collisionBox.segments.emplace_back(collisionBox.vertices.vertexSize(), collisionBox.lines.indexSize());
+                }
+
+                auto& segment = collisionBox.segments.back();
+                uint16_t index = segment.vertexLength;
+
+                collisionBox.vertices.emplace_back(CollisionBoxProgram::vertex(anchor, tl, maxZoom, placementZoom));
+                collisionBox.vertices.emplace_back(CollisionBoxProgram::vertex(anchor, tr, maxZoom, placementZoom));
+                collisionBox.vertices.emplace_back(CollisionBoxProgram::vertex(anchor, br, maxZoom, placementZoom));
+                collisionBox.vertices.emplace_back(CollisionBoxProgram::vertex(anchor, bl, maxZoom, placementZoom));
+
+                collisionBox.lines.emplace_back(index + 0, index + 1);
+                collisionBox.lines.emplace_back(index + 1, index + 2);
+                collisionBox.lines.emplace_back(index + 2, index + 3);
+                collisionBox.lines.emplace_back(index + 3, index + 0);
+
+                segment.vertexLength += vertexLength;
+                segment.indexLength += indexLength;
             }
         };
         populateCollisionBox(symbolInstance.textCollisionFeature);
diff --git a/src/mbgl/renderer/painter_symbol.cpp b/src/mbgl/renderer/painter_symbol.cpp
index d2dee5d99d..8c1948e458 100644
--- a/src/mbgl/renderer/painter_symbol.cpp
+++ b/src/mbgl/renderer/painter_symbol.cpp
@@ -130,7 +130,9 @@ void Painter::renderSymbol(PaintParameters& parameters,
                 uniforms::u_zoom::Value{ float(state.getZoom() * 10) },
                 uniforms::u_maxzoom::Value{ float((tile.id.canonical.z + 1) * 10) },
             },
-            *bucket.collisionBox.vertexBuffer
+            *bucket.collisionBox.vertexBuffer,
+            *bucket.collisionBox.indexBuffer,
+            bucket.collisionBox.segments
         );
     }
 }
diff --git a/src/mbgl/renderer/symbol_bucket.cpp b/src/mbgl/renderer/symbol_bucket.cpp
index 7fb3473967..81170646bc 100644
--- a/src/mbgl/renderer/symbol_bucket.cpp
+++ b/src/mbgl/renderer/symbol_bucket.cpp
@@ -29,6 +29,7 @@ void SymbolBucket::upload(gl::Context& context) {
 
     if (!collisionBox.vertices.empty()) {
         collisionBox.vertexBuffer = context.createVertexBuffer(std::move(collisionBox.vertices));
+        collisionBox.indexBuffer = context.createIndexBuffer(std::move(collisionBox.lines));
     }
 
     uploaded = true;
@@ -55,7 +56,7 @@ bool SymbolBucket::hasIconData() const {
 }
 
 bool SymbolBucket::hasCollisionBoxData() const {
-    return bool(collisionBox.vertexBuffer);
+    return !collisionBox.segments.empty();
 }
 
 } // namespace mbgl
diff --git a/src/mbgl/renderer/symbol_bucket.hpp b/src/mbgl/renderer/symbol_bucket.hpp
index f1fc3d324e..327049b280 100644
--- a/src/mbgl/renderer/symbol_bucket.hpp
+++ b/src/mbgl/renderer/symbol_bucket.hpp
@@ -52,8 +52,12 @@ public:
     } icon;
 
     struct CollisionBoxBuffer {
-        gl::VertexVector<CollisionBoxVertex, gl::Lines> vertices;
-        optional<gl::VertexBuffer<CollisionBoxVertex, gl::Lines>> vertexBuffer;
+        gl::VertexVector<CollisionBoxVertex> vertices;
+        gl::IndexVector<gl::Lines> lines;
+        std::vector<gl::Segment> segments;
+
+        optional<gl::VertexBuffer<CollisionBoxVertex>> vertexBuffer;
+        optional<gl::IndexBuffer<gl::Lines>> indexBuffer;
     } collisionBox;
 };