add very ugly camera-follows-player effect

docs/level-layout-doc.txt

@@ -0,0 +1,67 @@
+
+Y ↑
+  │  Bevy world ↑                                        LDtk-World ↓ 
+  │  (Y increases upward)                           (increases downward)
+  │
+  │     -32          -16            0            16            32
+  │      ┌────────────┬─────────────┬─────────────┬─────────────┐   │
+  │  32  │            │             │      L2     │             │-32│
+  │      │            │             │  (top-lvl)  │             │   │
+  │      │            │             │             │             │   │
+  │      ├────────────┼─────────────┼─────────────┼─────────────┤   │
+  │  16  │            │     L1      │   L0        │     L3      │-16│
+  │      │            │             │             │             │   │
+  │      │            │             │   (0,0)     │             │   │
+  │      ├────────────┼─────────────O─────────────┼─────────────┤   │
+  │   0  │            │             │   L4        │             │ 0 │
+  │      │            │             │             │             │   │
+  │      │            │             │             │             │   │
+  │      ├────────────┴─────────────┴─────────────┴─────────────┤   │
+  │ -16  │                        L5                            │ 16│
+  │      │                 (bottom-lvl)                         │   │
+  │      │                                                      │   │
+  │      └──────────────────────────────────────────────────────┘   ↓
+  │
+  └───────────────────────────────────────────────────────────────► X →
+        -32         -16            0            16            32
+```
+
+Legend
+──────
+• Each square = 16×16 tiles.
+• **Bevy Y** increases **upward** (↑).
+• **LDtk Y** (both world & inside level) increases **downward** (↓).
+
+Coordinate examples
+───────────────────
+Level L0  (at origin)
+  LDtk world anchor (top-left) = (0, -16)
+  Top-left corner in Bevy world   = (0, 16)
+
+Level L1  (left of origin)
+  LDtk world anchor               = (-16, -16)
+  Top-left corner in Bevy world   = (-16, 16)
+
+Level L2  (above origin)
+  LDtk world anchor               = (0, -32 )
+  Top-left corner in Bevy world   = (0, 32)
+
+Level L3  (right origin)
+  LDtk world anchor               = (16, -16)
+  Top-left corner in Bevy world   = (16, -16)
+
+Level L4  (below L3)
+  LDtk world anchor               = (0, 16)
+  Top-left corner in Bevy world   = (0, -16)
+
+Level L5 (below L4, spanning 4 x levels)
+  LDtk world anchor               = (-32, 32)
+  Top-left corner in Bevy world   = (-32, -32)
+
+
+Player's world-based gridcoords need to be converted to the internal coordinates for a level (so we can match it with
+the cached walls HashMap).
+To convert between world and in-level coords:
+
+lX = wX - level_world_x
+lY = wY - (-level_world_y - level_height)

src/demo/movement.rs

@@ -62,13 +62,14 @@ impl Default for MovementController {
 
 fn apply_movement(
     _time: Res<Time>,
+    mut camera: Query<&mut Transform, With<Camera>>,
     movement_query: Query<&MovementController, With<Player>>,
-    player_transform_query: Query<&Transform, With<Player>>,
+    player_transform_query: Query<&GlobalTransform, With<Player>>,
     mut players: Query<&mut GridCoords, With<Player>>,
     level_selection: Res<LevelSelection>,
     // level_walls: Res<LevelWalls>,
     level_walls: Res<MultiLevelWalls>,
-) {
+) -> Result {
     let level_selection_iid = match level_selection.as_ref() {
         LevelSelection::Iid(iid) => iid,
         _ => panic!("level should be selected by iid"),
@@ -93,7 +94,7 @@ fn apply_movement(
             } else {
                 // unrecognized intent, log a warning
                 warn!("Unrecognized intent: {:?}", controller.intent);
-                return;
+                return Ok(());
             };
             info!("player old absolute coords: {:?}", player_abs_coords);
             let destination = *player_abs_coords + movement_direction;
@@ -107,12 +108,17 @@ fn apply_movement(
                     player_transform_query.single()
                 );
                 // transform.translation += velocity.extend(0.0) * time.delta_secs();
+                if let Ok(player_transform) = player_transform_query.single() {
+                    let mut camera_transform = camera.single_mut()?;
+                    camera_transform.translation = player_transform.translation();
+                }
             } else {
                 info!("SDENG!");
             }
             level_walls.debug_collisions(level_selection_iid, &player_abs_coords);
         }
     }
+    Ok(())
 }
 
 #[derive(Component, Reflect)]