Phase 4.3: Grid auto-creates GridView with rendering property sync

Grid.__init__() now auto-creates a GridView that shares the Grid's
data via aliasing shared_ptr. This enables the Grid/GridView split:

- PyUIGridObject gains a `view` member (shared_ptr<UIGridView>)
- Grid.view property exposes the auto-created GridView (read-only)
- Rendering property setters (center_x/y, zoom, camera_rotation, x, y,
  w, h) sync changes to the view automatically
- Grid still works as UIDrawable in scenes (no substitution) — backward
  compatible with all existing code and subclasses
- GridView.grid returns the original Grid with identity preservation
- Explicit GridViews (created by user) are independent of Grid's own
  rendering properties

Addresses #252. All 260 tests pass, no breaking changes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/regression/grid_backward_compat_test.py

@@ -0,0 +1,126 @@
+"""Regression test for Grid backward compatibility with GridView shim (#252)."""
+import mcrfpy
+import sys
+
+def test_grid_creates_view():
+    """Grid auto-creates a GridView accessible via .view property."""
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = mcrfpy.Grid(grid_size=(10, 10), texture=tex, pos=(0, 0), size=(160, 160))
+    assert grid.view is not None, "Grid should auto-create a view"
+    assert isinstance(grid.view, mcrfpy.GridView)
+    print("PASS: Grid auto-creates view")
+
+def test_view_shares_grid_data():
+    """GridView created by shim shares the same grid data."""
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = mcrfpy.Grid(grid_size=(10, 10), texture=tex, pos=(0, 0), size=(160, 160))
+    view = grid.view
+
+    # View's grid should be the same Grid
+    assert view.grid is grid, "view.grid should be the same Grid"
+    assert view.grid.grid_w == 10
+    print("PASS: view shares grid data")
+
+def test_rendering_property_sync():
+    """Setting rendering properties on Grid syncs to the view."""
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = mcrfpy.Grid(grid_size=(10, 10), texture=tex, pos=(0, 0), size=(160, 160))
+    view = grid.view
+
+    grid.zoom = 3.0
+    assert abs(view.zoom - 3.0) < 0.01, f"View zoom should sync: {view.zoom}"
+
+    grid.center_x = 200.0
+    assert abs(view.center.x - 200.0) < 0.01, f"View center_x should sync: {view.center.x}"
+
+    grid.center_y = 150.0
+    assert abs(view.center.y - 150.0) < 0.01, f"View center_y should sync: {view.center.y}"
+
+    grid.camera_rotation = 45.0
+    # camera_rotation syncs through set_float_member
+    print("PASS: rendering properties sync to view")
+
+def test_grid_still_works_in_scene():
+    """Grid can still be appended to scenes and works as before."""
+    scene = mcrfpy.Scene("test_compat")
+    mcrfpy.current_scene = scene
+
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = mcrfpy.Grid(grid_size=(10, 10), texture=tex, pos=(0, 0), size=(160, 160))
+    scene.children.append(grid)
+
+    # Grid is in the scene as itself (not substituted)
+    assert len(scene.children) == 1
+    retrieved = scene.children[0]
+    assert type(retrieved).__name__ == "Grid", f"Expected Grid, got {type(retrieved).__name__}"
+    print("PASS: Grid works in scene as before")
+
+def test_grid_subclass_preserved():
+    """Grid subclasses maintain identity when appended to scene."""
+    scene = mcrfpy.Scene("test_subclass_compat")
+    mcrfpy.current_scene = scene
+
+    class MyGrid(mcrfpy.Grid):
+        pass
+
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = MyGrid(grid_size=(5, 5), texture=tex, pos=(0, 0), size=(80, 80))
+    scene.children.append(grid)
+
+    retrieved = scene.children[0]
+    assert isinstance(retrieved, MyGrid), f"Expected MyGrid, got {type(retrieved).__name__}"
+    print("PASS: Grid subclass identity preserved")
+
+def test_entity_operations_unaffected():
+    """Entity creation and manipulation still works normally."""
+    scene = mcrfpy.Scene("test_entity_compat")
+    mcrfpy.current_scene = scene
+
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = mcrfpy.Grid(grid_size=(20, 20), texture=tex, pos=(0, 0), size=(320, 320))
+    scene.children.append(grid)
+
+    for y in range(20):
+        for x in range(20):
+            grid.at(x, y).walkable = True
+            grid.at(x, y).transparent = True
+
+    e = mcrfpy.Entity((5, 5), grid=grid)
+    assert len(grid.entities) == 1
+    assert e.cell_x == 5
+    assert e.cell_y == 5
+    assert len(grid.at(5, 5).entities) == 1
+    print("PASS: entity operations unaffected")
+
+def test_gridview_independent_rendering():
+    """A GridView can have different rendering settings from the Grid."""
+    scene = mcrfpy.Scene("test_independent")
+    mcrfpy.current_scene = scene
+
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = mcrfpy.Grid(grid_size=(20, 20), texture=tex, pos=(0, 0), size=(320, 320))
+
+    # Create an explicit GridView with different settings
+    view2 = mcrfpy.GridView(grid=grid, pos=(350, 0), size=(160, 160), zoom=0.5)
+    scene.children.append(grid)
+    scene.children.append(view2)
+
+    # Grid and view2 should have different zoom
+    assert abs(grid.zoom - 1.0) < 0.01
+    assert abs(view2.zoom - 0.5) < 0.01
+
+    # Changing grid zoom doesn't affect explicit GridView
+    grid.zoom = 2.0
+    assert abs(view2.zoom - 0.5) < 0.01, "Explicit GridView should keep its own zoom"
+    print("PASS: GridView independent rendering")
+
+if __name__ == "__main__":
+    test_grid_creates_view()
+    test_view_shares_grid_data()
+    test_rendering_property_sync()
+    test_grid_still_works_in_scene()
+    test_grid_subclass_preserved()
+    test_entity_operations_unaffected()
+    test_gridview_independent_rendering()
+    print("All backward compatibility tests passed")
+    sys.exit(0)