feat: camera

packages/topdown/camera.js

@@ -0,0 +1,82 @@
+import {compose} from '@avocado/core';
+import {Vector} from '@avocado/math';
+import {EventEmitter, Property} from '@avocado/mixins';
+
+const decorate = compose(
+  EventEmitter,
+  Vector.Mixin('areaSize', 'areaWidth', 'areaHeight', {
+    default: [0, 0],
+    track: true,
+  }),
+  Property('drag', {
+    default: 1000,
+  }),
+  Vector.Mixin('position', 'x', 'y', {
+    default: [0, 0],
+    track: true,
+  }),
+  Vector.Mixin('realPosition', 'realX', 'realY', {
+    default: [0, 0],
+    track: true,
+  }),
+  Vector.Mixin('viewSize', 'viewWidth', 'viewHeight', {
+    default: [0, 0],
+    track: true,
+  }),
+);
+
+export class Camera extends decorate(class {}) {
+
+  constructor() {
+    super();
+    this.onAreaSizeChanged = this.onAreaSizeChanged.bind(this);
+    this.on('areaSizeChanged', this.onAreaSizeChanged);
+    this.onViewSizeChanged = this.onViewSizeChanged.bind(this);
+    this.on('viewSizeChanged', this.onViewSizeChanged);
+  }
+
+  destroy() {
+    this.off('areaSizeChanged', this.onAreaSizeChanged);
+    this.off('viewSizeChanged', this.onViewSizeChanged);
+  }
+
+  onAreaSizeChanged() {
+    this.position = this.position;
+  }
+
+  onViewSizeChanged() {
+    this.position = this.position;
+  }
+
+  get position() {
+    return super.position;
+  }
+
+  set position(position) {
+    if (0 === Vector.area(this.areaSize)) {
+      return super.position = position;
+    }
+    if (0 === Vector.area(this.viewSize)) {
+      return super.position = position;
+    }
+    const halfViewSize = Vector.scale(this.viewSize, 0.5);
+    super.position = Vector.clamp(
+      position,
+      halfViewSize,
+      Vector.sub(this.areaSize, halfViewSize)
+    );
+  }
+
+  tick(elapsed) {
+    if (Vector.equalsClose(this.position, this.realPosition, 1)) {
+      this.realPosition = this.position;
+      return;
+    }
+    this.realPosition = Vector.interpolate(
+      this.position,
+      this.realPosition,
+      this.drag * elapsed
+    );
+  }
+
+}

packages/topdown/index.js

@@ -1,3 +1,4 @@
+export {Camera} from './camera';
 export {Layer} from './layer';
 export {LayerView} from './layer-view';
 export {Room} from './room';