From e8daee85b06e14c24b4db4e7c250446a50be8d4b Mon Sep 17 00:00:00 2001
From: Erik Onarheim <erik.onarheim@gmail.com>
Date: Fri, 5 Jan 2024 19:56:01 -0600
Subject: [PATCH] fix: Issue with interpolation with parallax

---
 src/engine/Camera.ts                  | 9 +++++----
 src/engine/Graphics/GraphicsSystem.ts | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/engine/Camera.ts b/src/engine/Camera.ts
index d8a9a1b1c..14f50757f 100644
--- a/src/engine/Camera.ts
+++ b/src/engine/Camera.ts
@@ -317,9 +317,9 @@ export class Camera implements CanUpdate, CanInitialize {
   /**
    * Interpolated camera position if more draws are running than updates
    *
-   * Enabled when `Engine.fixedUpdateFps` is enabled
+   * Enabled when `Engine.fixedUpdateFps` is enabled, in all other cases this will be the same as pos
    */
-  public interpolatedPos: Vector = this.pos.clone();
+  public drawPos: Vector = this.pos.clone();
 
   private _oldPos = this.pos.clone();
 
@@ -626,6 +626,7 @@ export class Camera implements CanUpdate, CanInitialize {
       if (!this._posChanged) {
         this.pos = center;
       }
+      this.pos.clone(this.drawPos);
       // First frame bootstrap
 
       // Ensure camera tx is correct
@@ -781,7 +782,7 @@ export class Camera implements CanUpdate, CanInitialize {
    */
   public draw(ctx: ExcaliburGraphicsContext): void {
     // default to the current position
-    this.pos.clone(this.interpolatedPos);
+    this.pos.clone(this.drawPos);
 
     // interpolation if fixed update is on
     // must happen on the draw, because more draws are potentially happening than updates
@@ -790,7 +791,7 @@ export class Camera implements CanUpdate, CanInitialize {
       const interpolatedPos = this.pos.scale(blend).add(
         this._oldPos.scale(1.0 - blend)
       );
-      interpolatedPos.clone(this.interpolatedPos);
+      interpolatedPos.clone(this.drawPos);
       this.updateTransform(interpolatedPos);
     }
 
diff --git a/src/engine/Graphics/GraphicsSystem.ts b/src/engine/Graphics/GraphicsSystem.ts
index 361bbf017..187dce74e 100644
--- a/src/engine/Graphics/GraphicsSystem.ts
+++ b/src/engine/Graphics/GraphicsSystem.ts
@@ -112,7 +112,7 @@ export class GraphicsSystem extends System<TransformComponent | GraphicsComponen
         // https://doc.mapeditor.org/en/latest/manual/layers/#parallax-scrolling-factor
         // cameraPos * (1 - parallaxFactor)
         const oneMinusFactor = Vector.One.sub(parallax.parallaxFactor);
-        const parallaxOffset = this._camera.pos.scale(oneMinusFactor);
+        const parallaxOffset = this._camera.drawPos.scale(oneMinusFactor);
         this._graphicsContext.translate(parallaxOffset.x, parallaxOffset.y);
       }