Max Lyon
--- a/viewer/glow-extras/viewer/canvas.cc
+++ b/viewer/glow-extras/viewer/canvas.cc
-            if (l.pick_id >= 0)
-                has_picker = true;
-        }
-
-        // TODO: screen space dash size
-        if (!m.vertices().empty())
-        {
-            if (_state.two_colored_lines)
-                glow::warning() << "screen space two-colored lines are not supported";
-
-            auto r = gv::make_and_configure_renderable(gv::lines(pos).line_width_px(size), color3);

-            if (has_picker)
-                attach_picker(r, edge_pick_ids_data);
+    // two common functions for lines_px and lines_world:
+    auto add_line_to_mesh = [&](auto l, bool& has_picker, bool& has_normals)
--- a/viewer/glow-extras/viewer/canvas.cc
+++ b/viewer/glow-extras/viewer/canvas.cc
+    // two common functions for lines_px and lines_world:
+    auto add_line_to_mesh = [&](auto l, bool& has_picker, bool& has_normals)
+    {
+        auto v0 = m.vertices().add();
+        auto v1 = m.vertices().add();
+        pos[v0] = l.p0.pos;
+        pos[v1] = l.p1.pos;
+        color3[v0] = tg::color3(l.p0.color);
+        color3[v1] = tg::color3(l.p1.color);
+        color4[v0] = tg::color4(l.p0.color);
+        color4[v1] = tg::color4(l.p1.color);
+        size[v0] = l.p0.size;
+        size[v1] = l.p1.size;
+        normals[v0] = l.p0.normal;
+        normals[v1] = l.p1.normal;
+        has_normals |= tg::length_sqr(normals[v0]) + tg::length_sqr(normals[v1]) > 0;