Moved away from childof relationship!

Instead of using ChildOf, which has Transform implications, we created
our own relationship:

    ShapeBlocks(Vec<Entity>) <-> BlockOf { parent: Entity }

This relationship just informs how to place blocks with a
RelativePosition near their GridPosition parents without having to deal
with the Transform of the parent.

src/bin/tetris/main.rs

@@ -37,6 +37,8 @@ fn main() {
                 ),
                 sync_singleton_to_ui::<Shape>.run_if(any_component_changed::<Shape>),
                 sync_singleton_to_ui::<Orientation>.run_if(any_component_changed::<Orientation>),
+                check_collision.run_if(any_component_changed::<GridPosition>),
+                add_piece.run_if(not(any_with_component::<Shape>)),
             ),
         )
         .add_systems(Update, draw_grid)
@@ -45,6 +47,10 @@ fn main() {
 
 const SCALE: f32 = 30.0;
 
+// Declare the size of the play area
+const X_MAX: u32 = 10;
+const Y_MAX: u32 = 20;
+
 /// A shape, e.g., the long piece
 #[derive(Component, Debug, Default)]
 enum Shape {
@@ -72,11 +78,21 @@ impl Display for Shape {
     }
 }
 
+// The blocks making up this shape
+#[derive(Component)]
+#[relationship_target(relationship = BlockOf)]
+struct ShapeBlocks(Vec<Entity>);
+
 /// A part of a piece, i.e., a single square of a piece
 #[derive(Component, Debug)]
-struct ShapePiece;
+#[relationship(relationship_target = ShapeBlocks)]
+struct BlockOf {
+    #[relationship]
+    parent: Entity,
+}
 
 #[derive(Component, Debug)]
+#[require(GridPosition)]
 struct RelativePosition {
     x: i8,
     y: i8,
@@ -91,14 +107,14 @@ impl From<(i8, i8)> for RelativePosition {
 #[derive(Component, Debug, Clone, Copy, PartialEq)]
 #[require(Transform, Visibility)]
 struct GridPosition {
-    x: usize,
-    y: usize,
+    x: u32,
+    y: u32,
 }
 
 impl GridPosition {
     fn move_up(&self) -> Self {
         Self {
-            y: if self.y + 1 < 20 {
+            y: if self.y + 1 < Y_MAX {
                 self.y.saturating_add(1)
             } else {
                 self.y
@@ -123,7 +139,7 @@ impl GridPosition {
 
     fn move_right(&mut self) -> Self {
         Self {
-            x: if self.x + 1 < 10 {
+            x: if self.x + 1 < X_MAX {
                 self.x.saturating_add(1)
             } else {
                 self.x
@@ -131,11 +147,23 @@ impl GridPosition {
             y: self.y,
         }
     }
+
+    fn is_colliding_with(&self, other: &Self) -> bool {
+        self.x == other.x && self.y + 1 == other.y
+    }
+
+    fn add_offset(&self, RelativePosition { x: x1, y: y1 }: &RelativePosition) -> Self {
+        info!("{} + {}, {} + {}", self.x, *x1 as i32, self.y, *y1 as i32);
+        GridPosition {
+            x: self.x.checked_add_signed(*x1 as i32).unwrap(),
+            y: self.y.checked_add_signed(*y1 as i32).unwrap(),
+        }
+    }
 }
 
 impl Default for GridPosition {
     fn default() -> Self {
-        GridPosition { x: 5, y: 20 }
+        GridPosition { x: 5, y: Y_MAX }
     }
 }
 
@@ -154,8 +182,8 @@ impl From<&GridPosition> for Vec3 {
     }
 }
 
-impl From<(usize, usize)> for GridPosition {
-    fn from((x, y): (usize, usize)) -> GridPosition {
+impl From<(u32, u32)> for GridPosition {
+    fn from((x, y): (u32, u32)) -> GridPosition {
         GridPosition { x, y }
     }
 }
@@ -242,8 +270,6 @@ fn init_pieces(
         }),
         mesh: meshes.add(Rectangle::new(SCALE, SCALE)),
     });
-
-    commands.spawn((Orientation::default(), GridPosition::default(), Shape::T));
 }
 
 fn init_debug_ui(
@@ -273,8 +299,9 @@ fn set_piece(
         debug!("{e:?} {s:?} {o:?}");
         commands
             .entity(e)
-            .despawn_related::<Children>()
-            .with_children(|parent| {
+            // TODO: Just move entities, do not de/re-spawn
+            .despawn_related::<ShapeBlocks>()
+            .with_related_entities::<BlockOf>(|parent| {
             let mesh = visuals.mesh.clone();
             let mat = visuals.material.clone();
 
@@ -416,17 +443,17 @@ fn set_piece(
 
 fn set_relative_piece_positions(
     query: Query<
-        (Entity, &RelativePosition),
+        (Entity, &RelativePosition, &BlockOf),
         Or<(Added<RelativePosition>, Changed<RelativePosition>)>,
     >,
+    gp: Query<&GridPosition>,
     mut commands: Commands,
 ) {
-    query.iter().for_each(|(e, rp)| {
-        commands.entity(e).insert(Transform::from_xyz(
-            (rp.x as f32) * SCALE,
-            (rp.y as f32) * SCALE,
-            0.0,
-        ));
+    query.iter().for_each(|(e, rp, co)| {
+        let parent_gp = gp.get(co.parent).unwrap();
+        let gp: GridPosition = parent_gp.add_offset(rp);
+        info!("Inserting {:?} for {:?} to {:?}", gp, rp, e);
+        commands.entity(e).insert(gp);
     });
 }
 
@@ -481,14 +508,14 @@ fn draw_grid(mut gizmos: Gizmos) {
     gizmos
         .grid_2d(
             Isometry2d::IDENTITY,
-            UVec2::new(10, 20),
+            UVec2::new(X_MAX, Y_MAX),
             Vec2::new(SCALE, SCALE),
             GREEN,
         )
         .outer_edges();
 }
 
-fn falling(mut query: Query<&mut GridPosition, With<Shape>>) {
+fn falling(mut query: Query<&mut GridPosition>) {
     query.iter_mut().for_each(|mut gp| {
         let next = gp.move_down();
         if next != *gp {
@@ -511,3 +538,35 @@ fn clock_cycle(n: f32) -> impl FnMut(Res<Time>, Local<f32>) -> bool {
         }
     }
 }
+
+/// Check if the active piece is about to collide with the ground
+fn check_collision(
+    active: Query<&GridPosition, With<RelativePosition>>,
+    inactive: Query<&GridPosition, Without<RelativePosition>>,
+) {
+    // TODO: Easy optimizations
+    let hit = active.iter().any(|a| {
+        debug!("Checking: {:?}", a);
+        // Check if active piece is at floor
+        let hit_floor = a.y == 0;
+        // Check if active peice is near other pieces
+        let hit_piece = inactive.iter().any(|b| {
+            debug!("Checking against: {:?}", b);
+            a.is_colliding_with(b)
+        });
+
+        hit_floor || hit_piece
+    });
+
+    if hit {
+        info!("hit!")
+        // todo!("Do the thing!");
+    }
+}
+
+fn add_piece(
+    mut commands: Commands,
+) {
+    // TODO: Choose a different piece
+    commands.spawn((Orientation::default(), GridPosition::default(), Shape::T));
+}