Improve camera (#770)

examples/lib/stories/utils/camera_and_viewport.dart

@@ -24,7 +24,7 @@ class MovableSquare extends SquareComponent
     timer = Timer(3.0)
       ..stop()
       ..callback = () {
-        gameRef.camera.setRelativeOffset(Anchor.center.toVector2());
+        gameRef.camera.setRelativeOffset(Anchor.center);
       };
   }
 
@@ -50,7 +50,7 @@ class MovableSquare extends SquareComponent
   @override
   void onCollision(Set<Vector2> points, Collidable other) {
     if (other is Rock) {
-      gameRef.camera.setRelativeOffset(Anchor.topCenter.toVector2());
+      gameRef.camera.setRelativeOffset(Anchor.topCenter);
       timer.start();
     }
   }

packages/flame/CHANGELOG.md

@@ -7,6 +7,8 @@
  - Adding `SpriteAnimationGroupComponent`
  - Allow isometric tile maps with custom heights
  - Add a new renderRect method to Sprite
+ - Addresses the TODO to change the camera public APIs to take Anchors for relativePositions
+ - Adds methods to support moving the camera relative to its current position
 
 ## [1.0.0-rc9]
  - Fix input bug with other anchors than center

packages/flame/lib/src/game/camera.dart

@@ -179,6 +179,8 @@ class Camera extends Projector {
     update(0);
   }
 
+  // Coordinates
+
   @override
   Vector2 unprojectVector(Vector2 screenCoordinates) {
     return screenCoordinates * zoom + _position;
@@ -199,6 +201,13 @@ class Camera extends Projector {
     return worldCoordinates / zoom;
   }
 
+  /// This is the (current) absolute target of the camera, i.e., the
+  /// coordinate that should be on the top left, regardless of relative
+  /// offset, world boundaries or shake.
+  Vector2 absoluteTarget() {
+    return _currentCameraDelta ?? follow ?? Vector2.zero();
+  }
+
   // Follow
 
   /// Immediately snaps the camera to start following the [component].
@@ -214,7 +223,7 @@ class Camera extends Projector {
   /// position, set the components anchor to center.
   void followComponent(
     PositionComponent component, {
-    Vector2? relativeOffset,
+    Anchor relativeOffset = Anchor.center,
     Rect? worldBounds,
   }) {
     followVector2(
@@ -234,12 +243,12 @@ class Camera extends Projector {
   /// camera is allowed to move.
   void followVector2(
     Vector2 vector2, {
-    Vector2? relativeOffset,
+    Anchor relativeOffset = Anchor.center,
     Rect? worldBounds,
   }) {
     follow = vector2;
     this.worldBounds = worldBounds;
-    _targetRelativeOffset.setFrom(relativeOffset ?? Anchor.center.toVector2());
+    _targetRelativeOffset.setFrom(relativeOffset.toVector2());
     _currentRelativeOffset.setFrom(_targetRelativeOffset);
   }
 
@@ -249,9 +258,8 @@ class Camera extends Projector {
   /// you have two different options for the player to choose or your have a
   /// "dialog" camera that puts the player in a better place to show the
   /// dialog UI.
-  /// TODO(luan) this should be an anchor
+  void setRelativeOffset(Anchor newRelativeOffset) {
-  void setRelativeOffset(Vector2 newRelativeOffset) {
+    _targetRelativeOffset.setFrom(newRelativeOffset.toVector2());
-    _targetRelativeOffset.setFrom(newRelativeOffset);
   }
 
   Vector2 _screenDelta() {
@@ -259,7 +267,7 @@ class Camera extends Projector {
   }
 
   Vector2 _target() {
-    final target = _currentCameraDelta ?? follow ?? Vector2.zero();
+    final target = absoluteTarget();
     final attemptedTarget = target - _screenDelta();
 
     final bounds = worldBounds;
@@ -294,6 +302,13 @@ class Camera extends Projector {
 
   // Movement
 
+  /// Moves the camera by a given [displacement] (delta). This is the same as
+  /// [moveTo] but instead of providing an absolute end position, you can
+  /// provide a desired translation vector.
+  void translateBy(Vector2 displacement) {
+    moveTo(absoluteTarget() + displacement);
+  }
+
   /// Applies an ad-hoc movement to the camera towards the target, bypassing
   /// follow. Once it arrives the camera will not move until [resetMovement]
   /// is called.

packages/flame/test/game/camera_and_viewport_test.dart

@@ -214,7 +214,7 @@ void main() {
       game.add(p);
       game.update(0);
       // this would be a typical vertical shoot-em-up
-      game.camera.followComponent(p, relativeOffset: Vector2(0.5, 0.8));
+      game.camera.followComponent(p, relativeOffset: const Anchor(0.5, 0.8));
 
       expect(game.camera.position, Vector2.all(0.0));
       p.position.setValues(600.0, 2000.0);
@@ -296,7 +296,7 @@ void main() {
       final game = BaseGame();
       game.onResize(Vector2.all(200.0));
 
-      game.camera.setRelativeOffset(Anchor.center.toVector2());
+      game.camera.setRelativeOffset(Anchor.center);
 
       game.update(0);
       expect(game.camera.position, Vector2.zero());
@@ -339,8 +339,9 @@ void main() {
       game.add(p);
       game.camera.followComponent(
         p,
-        // this could be a typical mario-like platformer, where the player is more on the bottom left to allow the scenario to be seem
+        // this could be a typical mario-like platformer, where the player is
-        relativeOffset: Vector2(0.25, 0.25),
+        // more on the bottom left to allow the scenario to be seem
+        relativeOffset: const Anchor(0.25, 0.25),
         worldBounds: const Rect.fromLTWH(0, 0, 1000, 1000),
       );
 

packages/flame/test/game/projections_test.dart

@@ -102,7 +102,7 @@ void main() {
       game.onResize(Vector2.all(10));
 
       // no-op because the default is already top left
-      game.camera.setRelativeOffset(Anchor.topLeft.toVector2());
+      game.camera.setRelativeOffset(Anchor.topLeft);
       // top left corner of the screen is (-100, -100)
       game.camera.snapTo(Vector2.all(-100));
       // zoom is 2x, meaning every 1 unit you walk away of (-100, -100)
@@ -118,7 +118,7 @@ void main() {
 
       // note: in the current implementation, if we change the relative position
       // the zoom is still applied w.r.t. the top left of the screen
-      game.camera.setRelativeOffset(Anchor.center.toVector2());
+      game.camera.setRelativeOffset(Anchor.center);
       game.camera.snap();
 
       // that means that the center would be -100, -100 if the zoom was 1