From d8bf901c7647d9e4e458801c20a429666dee209e Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson@vistahigherlearning.com>
Date: Wed, 16 Dec 2020 07:54:21 -0500
Subject: node-2d: Fix camera target tracking.

---
 starling/node-2d.scm | 54 ++++++++++++++++++++--------------------------------
 1 file changed, 21 insertions(+), 33 deletions(-)

diff --git a/starling/node-2d.scm b/starling/node-2d.scm
index f7a40df..1559a54 100644
--- a/starling/node-2d.scm
+++ b/starling/node-2d.scm
@@ -134,9 +134,8 @@
 
 (define-class <camera-2d> ()
   (target #:accessor target #:init-form #f #:init-keyword #:target)
-  (offset #:getter offset #:init-form (vec2 0.0 0.0) #:init-keyword #:offset)
+  (offset #:accessor offset #:init-form (vec2 0.0 0.0) #:init-keyword #:offset)
   (position #:getter position #:init-form (vec2 0.0 0.0))
-  (last-position #:getter last-position #:init-form (vec2 0.0 0.0))
   (resolution #:getter resolution #:init-keyword #:resolution
               #:init-thunk default-resolution)
   (viewport #:getter viewport #:init-keyword #:viewport
@@ -155,31 +154,25 @@
 
 ;; This method can be overridden by subclasses to create custom camera
 ;; movement.
-(define-method (follow-target (camera <camera-2d>) dt)
-  (let ((pos (position camera))
-        (target-pos (position (target camera)))
-        (offset (offset camera)))
-    (set-vec2-x! pos (- (vec2-x offset) (vec2-x target-pos)))
-    (set-vec2-y! pos (- (vec2-y offset) (vec2-y target-pos)))))
-
-(define-method (update (camera <camera-2d>) dt)
-  (when (target camera)
-    (let ((pos (position camera))
-          (last-pos (last-position camera))
-          (m (view-matrix camera)))
-      (vec2-copy! pos last-pos)
-      (follow-target camera dt)
-      (unless (and (= (vec2-x pos) (vec2-x last-pos))
-                   (= (vec2-y pos) (vec2-y last-pos)))
-        (matrix4-translate! m pos)
-        (matrix4-mult! m m (projection-matrix camera))))))
+(define-method (follow-target (camera <camera-2d>))
+  (let ((p (position camera)))
+    (set-vec2! p 0.0 0.0)
+    (transform! (world-matrix (target camera)) p)
+    (vec2-mult! p -1.0)
+    (vec2-add! p (offset camera))))
 
 (define-syntax-rule (with-camera camera body ...)
-  (with-viewport (viewport camera)
-    (with-projection (if (target camera)
-                         (view-matrix camera)
-                         (projection-matrix camera))
-      body ...)))
+  (begin
+    (when (target camera)
+      (follow-target camera)
+      (let ((m (view-matrix camera)))
+        (matrix4-translate! m (position camera))
+        (matrix4-mult! m m (projection-matrix camera))))
+    (with-viewport (viewport camera)
+      (with-projection (if (target camera)
+                           (view-matrix camera)
+                           (projection-matrix camera))
+        body ...))))
 
 
 ;;;
@@ -193,19 +186,14 @@
   (cameras #:accessor cameras #:init-form (list (make <camera-2d>))
            #:init-keyword #:cameras))
 
-(define-method (update (canvas <canvas>) dt)
-  (for-each (lambda (camera)
-              (update camera dt))
-            (cameras canvas)))
-
 (define-method (render-tree (canvas <canvas>) alpha)
   (render canvas alpha)
   ;; Draw scene from the viewpoint of each camera.
   (for-each (lambda (camera)
               (with-camera camera
-                           (for-each-child (lambda (child)
-                                             (render-tree child alpha))
-                                           canvas)))
+                 (for-each-child (lambda (child)
+                                   (render-tree child alpha))
+                                 canvas)))
             (cameras canvas)))
 
 
-- 
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