a

2 files changed, 20 insertions, 1 deletions

diff --git a/editor/app.hpp b/editor/app.hpp
index b0f2aa8e..0d99a01f 100644
--- a/editor/app.hpp
+++ b/editor/app.hpp
@@ -29,6 +29,7 @@ struct critter;
 struct cursor_state final {
     Optional<Vector2i> pixel;
     Optional<global_coords> tile;
+    Optional<Vector2b> subpixel;
     bool in_imgui = false;
 };
 
diff --git a/editor/camera.cpp b/editor/camera.cpp
index 48a783cc..f9299a35 100644
--- a/editor/camera.cpp
+++ b/editor/camera.cpp
@@ -133,13 +133,31 @@ object_id app::object_at_cursor()
 void app::update_cursor_tile(const Optional<Vector2i>& pixel)
 {
     cursor.pixel = pixel;
+    // assert_invariant !!cursor.tile == !!cursor.subpixel;
     if (pixel)
     {
         auto coord = M->pixel_to_tile(Vector2d{*pixel});
-        cursor.tile = global_coords{coord.chunk(), coord.local(), _z_level};
+        auto tile = global_coords{coord.chunk(), coord.local(), _z_level};
+        cursor.tile = tile;
+
+        constexpr auto eps = 1e-6f;
+        constexpr auto m = TILE_SIZE2 * Vector2(1-eps, 1-eps);
+        const auto tile_ = Vector2(M->pixel_to_tile_(Vector2d(*pixel)));
+        const auto curchunk = Vector2(tile.chunk());
+        const auto subpixel_ = Vector2(std::fmod(tile_[0], 1.f), std::fmod(tile_[1], 1.f));
+        auto subpixel = m * Vector2(curchunk[0] < 0 ? 1 + subpixel_[0] : subpixel_[0],
+                                    curchunk[1] < 0 ? 1 + subpixel_[1] : subpixel_[1]);
+        constexpr auto half_tile = Vector2(iTILE_SIZE2/2);
+        subpixel -= half_tile;
+        subpixel.x() = Math::clamp(std::round(subpixel.x()), -half_tile.x(), half_tile.x()-1);
+        subpixel.y() = Math::clamp(std::round(subpixel.y()), -half_tile.y(), half_tile.y()-1);
+        cursor.subpixel = Vector2b(subpixel);
     }
     else
+    {
         cursor.tile = NullOpt;
+        cursor.subpixel = NullOpt;
+    }
 }
 
 } // namespace floormat