node-2d: Reduce matrix multiplication when camera is tracking a target.

1 files changed, 8 insertions, 8 deletions

diff --git a/starling/node-2d.scm b/starling/node-2d.scm
index 6fd80ba..095c5ca 100644
--- a/starling/node-2d.scm
+++ b/starling/node-2d.scm
@@ -155,19 +155,19 @@
 ;; This method can be overridden by subclasses to create custom camera
 ;; movement.
 (define-method (follow-target (camera <camera-2d>))
-  (let ((p (position camera)))
-    (set-vec2! p 0.0 0.0)
-    (transform! (world-matrix (target camera)) p)
+  (let ((p (position camera))
+        (m (view-matrix camera))
+        (w (world-matrix (target camera))))
+    (set-vec2! p (matrix4-x w) (matrix4-y w))
     (vec2-mult! p -1.0)
-    (vec2-add! p (offset camera))))
+    (vec2-add! p (offset camera))
+    (matrix4-translate! m (position camera))
+    (matrix4-mult! m m (projection-matrix camera))))
 
 (define-syntax-rule (with-camera 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))))
+      (follow-target camera))
     (with-viewport (viewport camera)
       (with-projection (if (target camera)
                            (view-matrix camera)