Tests pass so we are... almost cooking

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.

DESIGN.md

@@ -0,0 +1,45 @@
+# Design
+
+## Tetris
+
+Matrix Multiplication for rotating pieces.
+
+Each piece (shape) contains a Mat4 containing a representation of it's shape.
+For example:
+
+```
+0 1 0 0
+0 1 0 0
+0 1 0 0
+0 1 0 0
+```
+
+This is the classic `line` piece.
+
+And here it is on it's `up` side
+
+```
+0 0 0 0
+1 1 1 1
+0 0 0 0
+0 0 0 0
+```
+
+And here is the `t` piece
+
+```
+0 1 0
+1 1 1
+0 0 0
+```
+
+A matrix multiplication is applied to this Mat6 to achieve a piece rotation.
+
+When that matrix is updated, the 4 blocks parented to the shape are moved to reflect this new shape.
+
+This matrix also allows us to do checks to see if any of the blocks in the shape would intersect with another piece on the board.
+We can also check if a piece would go out of bounds during a move or rotation.
+
+We can use this to "plan -> validate -> commit" changes based on user input.
+
+Question: How the fuck do matrix multiplications work??

src/bin/tetris/main.rs

@@ -3,7 +3,7 @@
 
 use games::*;
 
-// TODO: Detect when piece is going to go out of bounds and restirct parent from moving there
+// *TODO: Detect when piece is going to go out of bounds and restirct parent from moving there
 // TODO: When shape touches the rest of the pieces, re-parent to line entity
 // TODO: When line is "full" (has 10 children) clear line and add to score
 
@@ -16,72 +16,99 @@ fn main() {
             ..default()
         })
         .init_state::<Falling>()
-        .add_systems(Startup, (init_pieces, init_debug_ui))
+        .add_systems(Startup, (init_world, init_debug_ui))
         .add_systems(
             Update,
             (
                 kb_input.run_if(on_event::<KeyboardInput>),
-                update_position,
                 falling
                     .run_if(in_state(Falling::On))
                     .run_if(clock_cycle(1.0)),
-                set_piece
-                    .run_if(any_component_added::<Shape>
+                set_shape.run_if(
+                    any_component_added::<Shape>
                         .or(any_component_changed::<Shape>)
                         .or(any_component_added::<Orientation>)
-                        .or(any_component_changed::<Orientation>)
-                    ),
-                set_relative_piece_positions.run_if(
-                    any_component_added::<RelativePosition>
-                        .or(any_component_changed::<RelativePosition>),
+                        .or(any_component_changed::<Orientation>),
                 ),
+                update_relative_position,
+                update_position.after(update_relative_position),
                 sync_singleton_to_ui::<Shape>.run_if(any_component_changed::<Shape>),
                 sync_singleton_to_ui::<Orientation>.run_if(any_component_changed::<Orientation>),
+                add_piece.run_if(not(any_with_component::<Shape>)),
+                clear_line.run_if(any_component_changed::<LineBlocks>),
             ),
         )
         .add_systems(Update, draw_grid)
+        .add_observer(deactive_shape)
         .run();
 }
 
 const SCALE: f32 = 30.0;
 
-/// A shape, e.g., the long piece
-#[derive(Component, Debug, Default)]
-enum Shape {
-    #[default]
-    O,
-    T,
-    L,
-    J,
-    S,
-    Z,
-    I,
-}
+// Declare the size of the play area
+const X_MAX: u32 = 10;
+const Y_MAX: u32 = 20;
 
-impl Display for Shape {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Shape::O => write!(f, "O"),
-            Shape::T => write!(f, "T"),
-            Shape::L => write!(f, "L"),
-            Shape::J => write!(f, "J"),
-            Shape::S => write!(f, "S"),
-            Shape::Z => write!(f, "Z"),
-            Shape::I => write!(f, "I"),
-        }
-    }
+// The blocks making up this shape
+#[derive(Component)]
+#[relationship_target(relationship = ShapeBlock)]
+struct ShapeBlocks(Vec<Entity>);
+
+/// A part of a piece, i.e., a single square of a piece
+#[derive(Component, Debug)]
+#[relationship(relationship_target = ShapeBlocks)]
+struct ShapeBlock {
+    #[relationship]
+    shape: Entity,
 }
 
+// The blocks making up this shape
+#[derive(Component, Default)]
+#[relationship_target(relationship = LineBlock)]
+struct LineBlocks(Vec<Entity>);
+
 /// A part of a piece, i.e., a single square of a piece
 #[derive(Component, Debug)]
-struct ShapePiece;
+#[require(Transform, Visibility)]
+#[relationship(relationship_target = LineBlocks)]
+struct LineBlock {
+    #[relationship]
+    line: Entity,
+}
+
+// A line holds up to 10 blocks before being cleared
+#[derive(Component, Debug)]
+struct Line(u8);
 
+// Just marks a block either of a shape or line
 #[derive(Component, Debug)]
+struct Block;
+
+#[derive(Component, Event, Debug, Clone, Copy, PartialEq)]
+#[require(GridPosition)]
 struct RelativePosition {
     x: i8,
     y: i8,
 }
 
+impl RelativePosition {
+    fn up() -> Self {
+        RelativePosition { x: 0, y: 1 }
+    }
+
+    fn down() -> Self {
+        RelativePosition { x: 0, y: -1 }
+    }
+
+    fn left() -> Self {
+        RelativePosition { x: -1, y: 0 }
+    }
+
+    fn right() -> Self {
+        RelativePosition { x: 1, y: 0 }
+    }
+}
+
 impl From<(i8, i8)> for RelativePosition {
     fn from((x, y): (i8, i8)) -> RelativePosition {
         RelativePosition { x, y }
@@ -91,14 +118,14 @@ 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 +150,7 @@ 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 +158,48 @@ impl GridPosition {
             y: self.y,
         }
     }
+
+    fn is_colliding_with(&self, other: &Self) -> bool {
+        self.x == other.x && self.y.saturating_sub(1) == other.y
+    }
+
+    fn add_relative(
+        &self,
+        RelativePosition { x: x1, y: y1 }: &RelativePosition,
+    ) -> Result<Self, GameError> {
+        let x = self
+            .x
+            .checked_add_signed(*x1 as i32)
+            .ok_or(GameError::OutOfBoundsLeft)?;
+        let y = self
+            .y
+            .checked_add_signed(*y1 as i32)
+            .ok_or(GameError::OutOfBoundsDown)?;
+        if x >= X_MAX {
+            // TODO: y > Y_MAX?
+            Err(GameError::OutOfBoundsRight)
+        } else {
+            debug!("Moving to {x},{y}");
+            Ok(GridPosition { x, y })
+        }
+    }
+}
+
+#[derive(Error, Debug, PartialEq)]
+enum GameError {
+    #[error("Coordinates are out of bounds: Left")]
+    OutOfBoundsLeft,
+    #[error("Coordinates are out of bounds: Right")]
+    OutOfBoundsRight,
+    #[error("Coordinates are out of bounds: Down")]
+    OutOfBoundsDown,
+    #[error("Coordiante collision")]
+    Collision,
 }
 
 impl Default for GridPosition {
     fn default() -> Self {
-        GridPosition { x: 5, y: 20 }
+        GridPosition { x: 5, y: Y_MAX }
     }
 }
 
@@ -154,8 +218,8 @@ 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 }
     }
 }
@@ -177,7 +241,7 @@ impl std::ops::AddAssign<&GridPosition> for GridPosition {
     }
 }
 
-#[derive(Component, Default, Debug)]
+#[derive(Component, Default, Event, Clone, Debug)]
 enum Orientation {
     #[default]
     Up,
@@ -230,7 +294,7 @@ struct Visuals {
     mesh: Handle<Mesh>,
 }
 
-fn init_pieces(
+fn init_world(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<ColorMaterial>>,
@@ -243,205 +307,392 @@ fn init_pieces(
         mesh: meshes.add(Rectangle::new(SCALE, SCALE)),
     });
 
-    commands.spawn((Orientation::default(), GridPosition::default(), Shape::T));
+    (0..20).for_each(|i| {
+        commands.spawn((Line(i), LineBlocks::default()));
+    });
 }
 
-fn init_debug_ui(
-    mut commands: Commands,
-) {
-    commands.spawn((Node {
+fn init_debug_ui(mut commands: Commands) {
+    commands
+        .spawn((
+            Node {
                 top: Val::Px(0.0),
                 left: Val::Px(0.0),
                 ..default()
-    }, DebuggingState::On)).with_children(|parent| {
+            },
+            DebuggingState::On,
+        ))
+        .with_children(|parent| {
             parent.spawn((
                 Node::default(),
                 children![
                     (Text::new("SHAPE"), SyncSingleton::<Shape>::default()),
-                (Text::new("ORIENTATION"), SyncSingleton::<Orientation>::default()),
-            ]
+                    (
+                        Text::new("ORIENTATION"),
+                        SyncSingleton::<Orientation>::default()
+                    ),
+                ],
             ));
         });
 }
 
-fn set_piece(
-    query: Query<(Entity, &Shape, &Orientation), Or<(Added<Shape>, Changed<Shape>, Added<Orientation>, Changed<Orientation>)>>,
+#[derive(Component, Debug)]
+enum Shape {
+    M4(Mat4),
+    M3(Mat3),
+}
+
+impl Default for Shape {
+    fn default() -> Self {
+        Self::new_t()
+    }
+}
+
+impl Display for Shape {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.as_ascii())
+    }
+}
+
+impl Shape {
+    fn from_mat4(input: Mat4) -> Self {
+        Self::M4(input)
+    }
+
+    fn from_mat3(input: Mat3) -> Self {
+        Self::M3(input)
+    }
+
+    fn new_o() -> Self {
+        Self::from_mat4(Mat4::from_cols_array_2d(&[
+            [0.,0.,0.,0.],
+            [0.,1.,1.,0.],
+            [0.,1.,1.,0.],
+            [0.,0.,0.,0.],
+        ]))
+    }
+
+    fn new_t() -> Self {
+        Self::from_mat3(Mat3::from_cols_array_2d(&[
+            [0.,1.,0.],
+            [1.,1.,1.],
+            [0.,0.,0.],
+        ]))
+    }
+
+    fn new_l() -> Self {
+        Self::from_mat4(Mat4::from_cols_array_2d(&[
+            [0.,0.,0.,0.],
+            [0.,1.,0.,0.],
+            [0.,1.,0.,0.],
+            [0.,1.,1.,0.],
+        ]))
+    }
+
+    fn new_j() -> Self {
+        Self::from_mat4(Mat4::from_cols_array_2d(&[
+            [0.,0.,0.,0.],
+            [0.,0.,1.,0.],
+            [0.,0.,1.,0.],
+            [0.,1.,1.,0.],
+        ]))
+    }
+
+    fn new_s() -> Self {
+        Self::from_mat4(Mat4::from_cols_array_2d(&[
+            [0.,0.,0.,0.],
+            [0.,1.,1.,0.],
+            [1.,1.,0.,0.],
+            [0.,0.,0.,0.],
+        ]))
+    }
+
+    fn new_z() -> Self {
+        Self::from_mat4(Mat4::from_cols_array_2d(&[
+            [0.,0.,0.,0.],
+            [1.,1.,0.,0.],
+            [0.,1.,1.,0.],
+            [0.,0.,0.,0.],
+        ]))
+    }
+
+    fn new_i() -> Self {
+        Self::from_mat4(Mat4::from_cols_array_2d(&[
+            [0.,0.,1.,0.],
+            [0.,0.,1.,0.],
+            [0.,0.,1.,0.],
+            [0.,0.,1.,0.],
+        ]))
+    }
+
+    // Rotates 90 degrees to the right
+    // https://stackoverflow.com/a/8664879
+    fn rotated(&self) -> Self {
+        match self {
+            Self::M4(inner) => {
+                let mut new_self = inner.transpose();
+                for i in 0..4 {
+                    let col = new_self.col_mut(i);
+                    *col = Vec4::new(col[3], col[2], col[1], col[0]);
+                }
+                Self::M4(new_self)
+            }
+            Self::M3(inner) => {
+                let mut new_self = inner.transpose();
+                for i in 0..3 {
+                    let col = new_self.col_mut(i);
+                    *col = Vec3::new(col[2], col[1], col[0]);
+                }
+                Self::M3(new_self)
+            }
+        }
+    }
+
+    fn rotate(&mut self) {
+        *self = self.rotated();
+    }
+
+    // TODO: return impl Iterator<Item = &RelativePosition>
+    fn relative_coordinates(&self) -> impl Iterator<Item = RelativePosition> {
+        let mut v: Vec<RelativePosition> = Vec::new();
+        match self {
+            Self::M4(inner) => {
+                for (i, y) in (-1..3).rev().enumerate() {
+                    let c = inner.col(i);
+                    for (j, x) in (-1..3).enumerate() {
+                        if c[j] == 1.0 {
+                            v.push(RelativePosition { x, y });
+                        }
+                    }
+                }
+            }
+            Self::M3(inner) => {
+                for (i, y) in (-1..2).rev().enumerate() {
+                    let c = inner.col(i);
+                    for (j, x) in (-1..2).enumerate() {
+                        if c[j] == 1.0 {
+                            v.push(RelativePosition { x, y });
+                        }
+                    }
+                }
+            }
+        };
+        v.into_iter()
+    }
+
+    fn computed_coordinates(&self, center: &GridPosition) -> impl Iterator<Item = Result<GridPosition, GameError>> {
+        self.relative_coordinates().map(|rp| center.add_relative(&rp))
+    }
+
+    fn as_ascii(&self) -> String {
+        let mut output = String::default();
+
+        match self {
+            Self::M4(this) => {
+                for i in 0..4 {
+                    let col = this.col(i).to_array();
+                    output += format!("{}{}{}{}\n", col[0], col[1], col[2], col[3]).as_str();
+                }
+            },
+            Self::M3(this) => {
+                for i in 0..3 {
+                    let col = this.col(i).to_array();
+                    output += format!("{}{}{}\n", col[0], col[1], col[2]).as_str();
+                }
+            },
+        };
+
+        output
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_shape_t() {
+        let mut shape = Shape::new_t();
+
+        let expected_up = "010\n\
+                           111\n\
+                           000\n";
+
+        let expected_right = "010\n\
+                              011\n\
+                              010\n";
+
+        let expected_down = "000\n\
+                             111\n\
+                             010\n";
+
+        let expected_left = "010\n\
+                             110\n\
+                             010\n";
+
+        assert_eq!(shape.as_ascii(), expected_up);
+        shape.rotate();
+        assert_eq!(shape.as_ascii(), expected_right);
+        shape.rotate();
+        assert_eq!(shape.as_ascii(), expected_down);
+        shape.rotate();
+        assert_eq!(shape.as_ascii(), expected_left);
+        shape.rotate();
+        assert_eq!(shape.as_ascii(), expected_up);
+    }
+
+    #[test]
+    fn test_shape_i() {
+        let mut shape = Shape::new_i();
+
+        let expected_up = "0010\n\
+                           0010\n\
+                           0010\n\
+                           0010\n";
+
+        let expected_right = "0000\n\
+                              0000\n\
+                              1111\n\
+                              0000\n";
+
+        let expected_down = "0100\n\
+                             0100\n\
+                             0100\n\
+                             0100\n";
+
+        let expected_left = "0000\n\
+                             1111\n\
+                             0000\n\
+                             0000\n";
+
+        assert_eq!(shape.as_ascii(), expected_up);
+        shape.rotate();
+        assert_eq!(shape.as_ascii(), expected_right);
+        shape.rotate();
+        assert_eq!(shape.as_ascii(), expected_down);
+        shape.rotate();
+        assert_eq!(shape.as_ascii(), expected_left);
+        shape.rotate();
+        assert_eq!(shape.as_ascii(), expected_up);
+    }
+
+    #[test]
+    fn test_relative_coordinates() {
+        let shape = Shape::new_t();
+
+        let expected: Vec<RelativePosition> = vec![
+            (0, 1).into(),
+            (-1, 0).into(),
+            (0, 0).into(),
+            (1, 0).into(),
+        ];
+
+        let actual: Vec<RelativePosition> = shape.relative_coordinates().collect();
+
+        assert_eq!(actual, expected);
+    }
+
+    #[test]
+    fn test_computed_coordinates() {
+        let shape = Shape::new_t();
+
+        let center = GridPosition { x: 5, y: 5 };
+
+        let expected: Vec<Result<GridPosition, GameError>> = vec![
+            Ok((5, 6).into()),
+            Ok((4, 5).into()),
+            Ok((5, 5).into()),
+            Ok((6, 5).into()),
+        ];
+
+        let actual: Vec<Result<GridPosition, GameError>> = shape.computed_coordinates(&center).collect();
+
+        assert_eq!(actual, expected);
+    }
+}
+
+fn set_shape(
+    query: Query<
+        (Entity, &Shape, &Orientation),
+        Or<(Added<Shape>, Changed<Shape>)>,
+    >,
+    mut blocks: Query<&mut RelativePosition, With<ShapeBlock>>,
     mut commands: Commands,
     visuals: Res<Visuals>,
 ) {
     query.iter().for_each(|(e, s, o)| {
-        debug!("{e:?} {s:?} {o:?}");
-        commands
-            .entity(e)
-            .despawn_related::<Children>()
-            .with_children(|parent| {
+        debug!("Setting piece: {e:?} {s:?} {o:?}");
+
         let mesh = visuals.mesh.clone();
         let mat = visuals.material.clone();
+        let positions: [RelativePosition;4] = todo!();
 
-            #[rustfmt::skip]
-            let piece_positions: [RelativePosition;4] = match s {
-                Shape::O => [
-                    (0,1).into(),(1,1).into(),
-                    (0,0).into(),(1,0).into()
-                ],
-                Shape::T => match o {
-                    Orientation::Up => [
-                                      (0,1).into(),
-                        (-1,0).into(),(0,0).into(),(1,0).into(),
-                    ],
-                    Orientation::Down => [
-                        (-1,0).into(),(0,0).into(),(1,0).into(),
-                                      (0,-1).into(),
-                    ],
-                    Orientation::Right => [
-                        (0,1).into(),
-                        (0,0).into(), (1,0).into(),
-                        (0,-1).into(),
-                    ],
-                    Orientation::Left => [
-                                      (0,1).into(),
-                        (-1,0).into(),(0,0).into(),
-                                      (0,-1).into(),
-                    ]
-                },
-                Shape::L => match o {
-                    Orientation::Up => [
-                        (0,1).into(),
-                        (0,0).into(),
-                        (0,-1).into(),(1,-1).into(),
-                    ],
-                    Orientation::Down => [
-                        (-1,1).into(),(0,1).into(),
-                                      (0,0).into(),
-                                      (0,-1).into(),
-                    ],
-                    Orientation::Right => [
-                        (-1,0).into(),(0,0).into(),(1,0).into(),
-                        (-1,-1).into(),
-                    ],
-                    Orientation::Left => [
-                                                   (1,1).into(),
-                        (-1,0).into(),(0,0).into(),(1,0).into(),
-                    ],
-                },
-                Shape::J => match o {
-                    Orientation::Up => [
-                                      (0,1).into(),
-                                      (0,0).into(),
-                        (-1,-1).into(),(0,-1).into(),
-                    ],
-                    Orientation::Down => [
-                        (0,1).into(),(1,1).into(),
-                        (0,0).into(),
-                        (0,-1).into(),
-                    ],
-                    Orientation::Left => [
-                        (-1,0).into(),(0,0).into(),(1,0).into(),
-                                                   (1,-1).into(),
-                    ],
-                    Orientation::Right => [
-                        (-1,1).into(),
-                        (-1,0).into(),(0,0).into(),(1,0).into()
-                    ],
-                },
-                Shape::S => match o {
-                    Orientation::Up => [
-                                       (0,0).into(),(1,0).into(),
-                        (-1,-1).into(),(0,-1).into(),
-                    ],
-                    Orientation::Down => [
-                                      (0,1).into(),(1,1).into(),
-                        (-1,0).into(),(0,0).into(),
-                    ],
-                    Orientation::Right => [
-                        (-1,1).into(),
-                        (-1,0).into(),(0,0).into(),
-                                      (0,-1).into(),
-                    ],
-                    Orientation::Left => [
-                        (0,1).into(),
-                        (0,0).into(),(1,0).into(),
-                                     (1,-1).into(),
-                    ],
-                },
-                Shape::Z => match o {
-                    Orientation::Up => [
-                        (-1,0).into(),(0,0).into(),
-                                      (0,-1).into(),(1,-1).into(),
-                    ],
-                    Orientation::Down => [
-                        (-1,1).into(),(0,1).into(),
-                                      (0,0).into(),(1,0).into(),
-                    ],
-                    Orientation::Left => [
-                                     (1,1).into(),
-                        (0,0).into(),(1,0).into(),
-                        (0,-1).into(),
-                    ],
-                    Orientation::Right => [
-                                      (0,1).into(),
-                        (-1,0).into(),(0,0).into(),
-                        (-1,-1).into(),
-                    ],
-                },
-                // TODO: This does not match tetris!
-                Shape::I => match o {
-                    Orientation::Up => [
-                        (0,2).into(),
-                        (0,1).into(),
-                        (0,0).into(),
-                        (0,-1).into(),
-                    ],
-                    Orientation::Down => [
-                        (-1,2).into(),
-                        (-1,1).into(),
-                        (-1,0).into(),
-                        (-1,-1).into(),
-                    ],
-                    Orientation::Left => [
-                        (-2,0).into(),(-1,0).into(),(0,0).into(),(1,0).into(),
-                    ],
-                    Orientation::Right => [
-                        (-2,1).into(),(-1,1).into(),(0,1).into(),(1,1).into(),
-                    ]
-                }
-            };
+        // todo: map positions to coordinates
 
-            piece_positions.into_iter().for_each(|rp| {
-                parent.spawn((Mesh2d(mesh.clone()), MeshMaterial2d(mat.clone()), rp));
+        if blocks.is_empty() {
+            commands
+                .entity(e)
+                .with_related_entities::<ShapeBlock>(|parent| {
+                    positions.into_iter().for_each(|rp| {
+                        parent
+                            .spawn((Mesh2d(mesh.clone()), MeshMaterial2d(mat.clone()), rp, Block))
+                            .observe(movement);
+                    });
                 });
+        } else {
+            let mut p = positions.into_iter();
+            blocks.iter_mut().for_each(|mut rp| {
+                *rp = p.next().unwrap();
             });
+        }
     });
 }
 
-fn set_relative_piece_positions(
-    query: Query<
-        (Entity, &RelativePosition),
-        Or<(Added<RelativePosition>, Changed<RelativePosition>)>,
+fn update_position(
+    mut changed: Query<
+        (Entity, &GridPosition, &mut Transform),
+        Or<(Added<GridPosition>, Changed<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,
-        ));
+    changed.iter_mut().for_each(|(e, gp, mut t)| {
+        let v3: Vec3 = gp.into();
+        debug!(
+            "Updating {e} with grid position {:?} to coordinates {:?}",
+            gp, v3
+        );
+
+        debug_assert!(gp.x < X_MAX, "block x > x_max");
+        t.translation = gp.into();
     });
 }
 
-fn update_position(mut query: Query<(&GridPosition, &mut Transform), Changed<GridPosition>>) {
-    query.iter_mut().for_each(|(gp, mut t)| {
-        t.translation = gp.into();
-        debug!("Updating position {:?}", t.translation);
+fn update_relative_position(
+    shape: Single<&GridPosition, With<ShapeBlocks>>,
+    mut query: Query<
+        (Entity, &mut GridPosition, &RelativePosition),
+        (
+            Without<ShapeBlocks>,
+            Or<(Added<RelativePosition>, Changed<RelativePosition>)>,
+        ),
+    >,
+) {
+    query.iter_mut().for_each(|(e, mut gp, rp)| {
+        debug!(
+            "Updating {e} grid position to {:?} + {:?} = {:?}",
+            gp,
+            rp,
+            gp.add_relative(rp).unwrap()
+        );
+        *gp = (*shape).add_relative(rp).unwrap();
     });
 }
 
 fn kb_input(
     mut events: EventReader<KeyboardInput>,
-    mut query: Query<(&mut GridPosition, &mut Orientation, &mut Shape)>,
+    mut query: Query<(Entity, &Orientation, &mut Shape)>,
     curr: Res<State<Falling>>,
     mut next: ResMut<NextState<Falling>>,
+    mut commands: Commands,
 ) {
     events.read().for_each(
         |KeyboardInput {
@@ -450,25 +701,33 @@ fn kb_input(
             if let ButtonState::Pressed = state {
                 // TODO: Restict movement based on size/orientation of piece
                 // Check if children would be outside play area...
-                query.iter_mut().for_each(|(mut gp, mut o, mut s)| {
+                query.iter_mut().for_each(|(e, o, mut s)| {
                     match key_code {
                         // Up arrow should rotate if in falling mode
                         // Only move up if in falling::off mode
-                        KeyCode::ArrowUp => *o = o.prev(),
-                        KeyCode::ArrowDown => *gp = gp.move_down(),
-                        KeyCode::ArrowLeft => *gp = gp.move_left(),
-                        KeyCode::ArrowRight => *gp = gp.move_right(),
+                        KeyCode::ArrowUp => {
+                            commands.entity(e).trigger(o.prev());
+                        }
+                        KeyCode::ArrowDown => {
+                            commands.entity(e).trigger(RelativePosition::down());
+                        }
+                        KeyCode::ArrowLeft => {
+                            commands.entity(e).trigger(RelativePosition::left());
+                        }
+                        KeyCode::ArrowRight => {
+                            commands.entity(e).trigger(RelativePosition::right());
+                        }
                         KeyCode::Space => next.set(match curr.get() {
                             Falling::On => Falling::Off,
                             Falling::Off => Falling::On,
                         }),
-                        KeyCode::Digit1 => *s = Shape::T,
-                        KeyCode::Digit2 => *s = Shape::O,
-                        KeyCode::Digit3 => *s = Shape::L,
-                        KeyCode::Digit4 => *s = Shape::J,
-                        KeyCode::Digit5 => *s = Shape::S,
-                        KeyCode::Digit6 => *s = Shape::Z,
-                        KeyCode::Digit7 => *s = Shape::I,
+                        KeyCode::Digit1 => *s = Shape::new_t(),
+                        KeyCode::Digit2 => *s = Shape::new_o(),
+                        KeyCode::Digit3 => *s = Shape::new_l(),
+                        KeyCode::Digit4 => *s = Shape::new_j(),
+                        KeyCode::Digit5 => *s = Shape::new_s(),
+                        KeyCode::Digit6 => *s = Shape::new_z(),
+                        KeyCode::Digit7 => *s = Shape::new_i(),
                         _ => (),
                     }
                 });
@@ -481,25 +740,22 @@ 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>>) {
-    query.iter_mut().for_each(|mut gp| {
-        let next = gp.move_down();
-        if next != *gp {
-            *gp = next;
-        } else {
-            // Remove the falling component from this entity
-        }
+fn falling(mut shape: Query<Entity, With<Shape>>, mut commands: Commands) {
+    shape.iter_mut().for_each(|e| {
+        info!("Making {:?} fall", e);
+        commands.entity(e).trigger(RelativePosition::down());
     });
 }
 
 // Run condition that returns `true` every `n` seconds
+// TODO: Update a resource with the current tick
 fn clock_cycle(n: f32) -> impl FnMut(Res<Time>, Local<f32>) -> bool {
     move |t: Res<Time>, mut buf: Local<f32>| -> bool {
         *buf += t.delta_secs();
@@ -511,3 +767,106 @@ fn clock_cycle(n: f32) -> impl FnMut(Res<Time>, Local<f32>) -> bool {
         }
     }
 }
+
+fn add_piece(mut commands: Commands) {
+    // TODO: Choose a different piece
+    commands
+        .spawn((Orientation::default(), GridPosition::default(), Shape::default()))
+        .observe(movement)
+        .observe(rotation);
+}
+
+/// When a line reaches 10 blocks, clear it
+fn clear_line(
+    lines: Query<(Entity, &LineBlocks), (With<LineBlocks>, Changed<LineBlocks>)>,
+    mut commands: Commands,
+) {
+    lines.iter().for_each(|(e, lb)| {
+        if lb.0.len() == 10 {
+            commands.entity(e).despawn_related::<LineBlocks>();
+            // TODO: re-parent all blocks above this to the next line down
+            // TODO: Parent blocks to lines for movement
+        }
+    });
+}
+
+fn movement(
+    trigger: Trigger<RelativePosition>,
+    mut grid_positions: Query<&mut GridPosition, Or<(With<RelativePosition>, With<Shape>)>>,
+    parent: Query<&ShapeBlocks>,
+    inactive: Query<
+        &GridPosition,
+        (
+            Without<RelativePosition>,
+            Without<Shape>,
+        ),
+    >,
+    mut commands: Commands,
+) {
+    // Do a bunch of checks if this move is valid
+    for block in parent.iter_descendants(trigger.target()) {
+        let block_gp = grid_positions.get(block).unwrap();
+
+        match block_gp.add_relative(trigger.event()) {
+            Err(GameError::OutOfBoundsLeft) | Err(GameError::OutOfBoundsRight) => {
+                // Hit the left/right wall, just ignore this move
+                return;
+            }
+            Err(GameError::OutOfBoundsDown) => {
+                commands.entity(trigger.target()).remove::<Shape>();
+                return;
+            }
+            Err(GameError::Collision) => {
+                // Do nothing. add_relative does not return this variant
+            }
+            Ok(new_block_gp) => {
+                let collision = inactive
+                    .iter()
+                    .any(|inactive_block_gp| new_block_gp == *inactive_block_gp);
+
+                if collision {
+                    commands.entity(trigger.target()).remove::<Shape>();
+                }
+            }
+        }
+    }
+
+    // Move shape itself
+    if let Ok(mut shape_gp) = grid_positions.get_mut(trigger.target()) {
+        *shape_gp = shape_gp.add_relative(trigger.event()).unwrap();
+    }
+
+    // Move the blocks of this shape
+    parent.iter_descendants(trigger.target()).for_each(|block| {
+        info!("Propogating movement {:?} to child {:?}", trigger.event(), block);
+        commands.entity(block).trigger(*trigger.event());
+    });
+}
+
+fn rotation(trigger: Trigger<Orientation>, mut q: Query<&mut Orientation>) {
+    let mut o = q.get_mut(trigger.target()).unwrap();
+    // If children would go out of bounds going left, move slightly to the right
+    //    If that would cause collision, deactive piece
+    // If children would go out of bounds going right, move slightly to the left
+    //    If that would cause collision, deactive piece
+    // If children would not go out of bounds going down
+    *o = trigger.event().clone();
+}
+
+// TODO: Just despawn?
+fn deactive_shape(
+    trigger: Trigger<OnRemove, Shape>,
+    parent: Query<&ShapeBlocks>,
+    mut commands: Commands,
+) {
+    let v: Vec<Entity> = parent.iter_descendants(trigger.target()).collect();
+    parent.iter_descendants(trigger.target()).for_each(|block| {
+        commands.entity(block).remove::<RelativePosition>();
+    });
+    commands
+        .entity(trigger.target())
+        .remove_related::<ShapeBlock>(v.as_slice())
+        .despawn();
+}
+
+// TODO: When Orientation changed, perform matrix multiplication or something(?)