1 files changed, 38 insertions, 13 deletions
diff --git a/sly/scene.scm b/sly/scene.scm
index 9314eac..7f6ec5e 100644
--- a/sly/scene.scm
+++ b/sly/scene.scm
@@ -46,6 +46,7 @@
   (prev-position scene-node-prev-position set-scene-node-prev-position!)
   (prev-scale scene-node-prev-scale set-scene-node-prev-scale!)
   (prev-rotation scene-node-prev-rotation set-scene-node-prev-rotation!)
+  (transform scene-node-transform set-scene-node-transform!)
   (uniforms scene-node-uniforms)
   (children scene-node-children))
 
@@ -56,10 +57,21 @@
                            (uniforms '())
                            (children '())
                            #:allow-other-keys)
-  (%make-scene-node position scale rotation uniforms children))
+  (let ((node (%make-scene-node position scale rotation uniforms children)))
+    (update-scene-node node)
+    (recompute-transform! node 0)
+    node))
 
 (define scene-node make-scene-node)
 
+(define (scene-node-dirty? node)
+  (define (different? a b)
+    (not (equal? (a node) (b node))))
+
+  (or (different? scene-node-position scene-node-prev-position)
+      (different? scene-node-scale scene-node-prev-scale)
+      (different? scene-node-rotation scene-node-prev-rotation)))
+
 (define (scene-root . children)
   (scene-node #:children children))
 
@@ -81,20 +93,33 @@
       current
       (vector-interpolate prev current alpha)))
 
+(define (recompute-transform! node alpha)
+  (signal-let ((position (scene-node-position node))
+               (%scale (scene-node-scale node))
+               (rotation (scene-node-rotation node)))
+    (let ((t (transform*
+              (translate
+               (interpolate position
+                            (scene-node-prev-position node)
+                            alpha))
+              (quaternion->transform
+               (quaternion-slerp rotation
+                                 (scene-node-prev-rotation node)
+                                 alpha))
+              (scale (interpolate %scale
+                                  (scene-node-prev-scale node)
+                                  alpha)))))
+      (set-scene-node-transform! node t)
+      t)))
+
 (define (draw-scene-node node alpha transform)
   (signal-let ((node node))
     (if (mesh? node)
         (draw-mesh node `(("mvp" ,transform)))
-        (signal-let ((position (scene-node-position node))
-                     (%scale (scene-node-scale node))
-                     (rotation (scene-node-rotation node))
-                     (children (scene-node-children node)))
-          (let ((transform (transform*
-                            transform
-                            (translate
-                             (interpolate position
-                                          (scene-node-prev-position node)
-                                          alpha))
-                            (quaternion->transform rotation)
-                            (scale %scale))))
+        (let ((transform
+               (transform* transform
+                           (if (scene-node-dirty? node)
+                               (recompute-transform! node alpha)
+                               (scene-node-transform node)))))
+          (signal-let ((children (scene-node-children node)))
             (for-each (cut draw-scene-node <> alpha transform) children))))))