From f38127a4ad9f9867a115cd50caa30a4a1c6645de Mon Sep 17 00:00:00 2001
From: Adrien Burgun <adrien.burgun@orange.fr>
Date: Sun, 2 Apr 2023 15:59:04 +0200
Subject: [PATCH] :sparkles: Create a class for PannableState, add inverse
 transformation

---
 src/index.js             | 71 ++++++++++++++++++++++++++--------------
 src/solid/usePannable.ts | 13 ++++----
 2 files changed, 54 insertions(+), 30 deletions(-)

diff --git a/src/index.js b/src/index.js
index 837b000..1fe9614 100644
--- a/src/index.js
+++ b/src/index.js
@@ -313,17 +313,6 @@ export function attachTouch(element, options = {}) {
     }
 }
 
-/**
- * @typedef {object} PannableState
- *   An immutable object returned by `Pannable::getState()`
- * @prop {number} dx
- * @prop {number} dy
- * @prop {number} scale
- * @prop {number} logScale
- * @prop {(x: number, y: number) => [x: number, y: number]} get
- *   Returns the transformed coordinates
- **/
-
 /**
  * @typedef {object} PannableOptions
  * @prop {number=} downscale
@@ -391,19 +380,8 @@ export class Pannable {
     }
 
     /** @returns {PannableState} **/
-    getState() {
-        const scale = this.scale;
-        const dx = this.dx;
-        const dy = this.dy;
-        return {
-            dx,
-            dy,
-            logScale: this.logScale,
-            scale,
-            get: (x, y) => {
-                return [x * scale + dx, y * scale + dy];
-            }
-        };
+    getState(cx = 0, cy = 0) {
+        return new PannableState(this.dx + cx, this.dy + cy, this.logScale);
     }
 
     /**
@@ -448,6 +426,51 @@ export class Pannable {
     }
 }
 
+/**
+ * An immutable view of `Pannable`, returned by `Pannable::getState`.
+ **/
+export class PannableState {
+    /**
+     * @param {number} dx
+     * @param {number} dy
+     * @param {number} logScale
+     **/
+    constructor(dx, dy, logScale) {
+        /** @readonly The X offset to move coordinates by *after* multiplying them by `scale` **/
+        this.dx = dx;
+        /** @readonly The Y offset to move coordinates by *after* multiplying them by `scale` **/
+        this.dy = dy;
+        /** @readonly The base-2 logarithm of `scale`, used internally for precision purposes **/
+        this.logScale = logScale;
+        /** @readonly The zoom strength **/
+        this.scale = Math.pow(2, logScale);
+    }
+
+    /**
+     * Transforms the input coordinates from the "pannable" coordinates
+     * to the "real" coordinates (what you will display on screen)
+     *
+     * @param {number} x The X "pannable" coordinate
+     * @param {number} y The Y "pannable" coordinate
+     * @returns {[x: number, y: number]}
+     **/
+    get(x, y) {
+        return [x * this.scale + this.dx, y * this.scale + this.dy];
+    }
+
+    /**
+     * Transforms the input coordinates from the "real" coordinates (where they are on screen)
+     * to the "pannable" coordinates; this is the inverse operation of the `PannableState::get` method.
+     *
+     * @param {number} x The X "real" coordinate
+     * @param {number} y The Y "real" coordinate
+     * @returns {[x: number, y: number]}
+     **/
+    inverse(x, y) {
+        return [(x - this.dx) / this.scale, (y - this.dy) / this.scale];
+    }
+}
+
 /**
  * @typedef {PannableOptions & {
  *   onUpdate?: (state: PannableState) => void,
diff --git a/src/solid/usePannable.ts b/src/solid/usePannable.ts
index a675d8f..ea84e41 100644
--- a/src/solid/usePannable.ts
+++ b/src/solid/usePannable.ts
@@ -28,13 +28,14 @@ export function usePannable(config: PannableOptions & UsePannableOptions) {
             return newState;
         },
         getState: () => {
-            const result = state();
+            const preTransformed = state();
             const [cx, cy] = center();
-            return {
-                ...result,
-                dx: result.dx + cx,
-                dy: result.dy + cy,
-            };
+
+            return new PannableState(
+                preTransformed.dx + cx,
+                preTransformed.dy + cy,
+                preTransformed.logScale
+            );
         }
     };
 }