From b345d228b38cf6d3b5206327d63fe969adc42811 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Tue, 28 Aug 2018 09:00:16 -0400
Subject: node: Add visible? flag.

---
 starling/node-2d.scm | 41 +++++++++++++++++++++--------------------
 starling/node.scm    | 24 +++++++++++++++++++-----
 2 files changed, 40 insertions(+), 25 deletions(-)

diff --git a/starling/node-2d.scm b/starling/node-2d.scm
index a0b2746..368e8a2 100644
--- a/starling/node-2d.scm
+++ b/starling/node-2d.scm
@@ -314,26 +314,27 @@
   (next-method))
 
 (define-method (render* (node <node-2d>) alpha)
-  ;; Compute the linearly interpolated rendering position, in the case
-  ;; that node has moved since the last update.
-  (let ((p (position node))
-        (lp (last-position node))
-        (rp (render-position node))
-        (beta (- 1.0 alpha)))
-    (unless (and (= (vec2-x lp) (vec2-x rp))
-                 (= (vec2-y lp) (vec2-y rp)))
-      (set-vec2-x! rp (+ (* (vec2-x p) alpha) (* (vec2-x lp) beta)))
-      (set-vec2-y! rp (+ (* (vec2-y p) alpha) (* (vec2-y lp) beta)))
-      (set! (dirty-matrix? node) #t)))
-  ;; Recompute dirty matrices.
-  (when (dirty-matrix? node)
-    (compute-matrices! node)
-    (set! (dirty-matrix? node) #f)
-    ;; If the parent is dirty, all the children need to be marked as
-    ;; dirty, too.
-    (for-each (lambda (node)
-                (set! (dirty-matrix? node) #t))
-              (children node)))
+  (when (visible? node)
+    ;; Compute the linearly interpolated rendering position, in the case
+    ;; that node has moved since the last update.
+    (let ((p (position node))
+          (lp (last-position node))
+          (rp (render-position node))
+          (beta (- 1.0 alpha)))
+      (unless (and (= (vec2-x lp) (vec2-x rp))
+                   (= (vec2-y lp) (vec2-y rp)))
+        (set-vec2-x! rp (+ (* (vec2-x p) alpha) (* (vec2-x lp) beta)))
+        (set-vec2-y! rp (+ (* (vec2-y p) alpha) (* (vec2-y lp) beta)))
+        (set! (dirty-matrix? node) #t)))
+    ;; Recompute dirty matrices.
+    (when (dirty-matrix? node)
+      (compute-matrices! node)
+      (set! (dirty-matrix? node) #f)
+      ;; If the parent is dirty, all the children need to be marked as
+      ;; dirty, too.
+      (for-each (lambda (node)
+                  (set! (dirty-matrix? node) #t))
+                (children node))))
   (next-method))
 
 (define-method (activate (node <node-2d>))
diff --git a/starling/node.scm b/starling/node.scm
index 4ce46dd..51866d2 100644
--- a/starling/node.scm
+++ b/starling/node.scm
@@ -31,11 +31,14 @@
             agenda
             booted?
             active?
+            visible?
             on-boot
             on-enter
             on-exit
             activate
             deactivate
+            show
+            hide
             update
             update*
             render
@@ -63,7 +66,10 @@
   ;; Flips to #t upon first entering a scene.
   (booted? #:accessor booted? #:init-form #f)
   ;; Flips to #t when node is part of current scene.
-  (active? #:accessor active? #:init-form #f))
+  (active? #:accessor active? #:init-form #f)
+  ;; Determines whether or not the node and all of its children are
+  ;; rendered.
+  (visible? #:accessor visible? #:init-form #t #:init-keyword #:visible?))
 
 (define (for-each-child proc node)
   (for-each proc (children node)))
@@ -97,8 +103,9 @@ the next update represented as a ratio in the range [0, 1]."
   "Render NODE and all of its children, recursively.
 ALPHA is the distance between the previous update and the next update
 represented as a ratio in the range [0, 1]."
-  (render node alpha)
-  (for-each-child (lambda (child) (render* child alpha)) node))
+  (when (visible? node)
+    (render node alpha)
+    (for-each-child (lambda (child) (render* child alpha)) node)))
 
 (define-method (on-boot (node <node>))
   "Perform initialization tasks for NODE."
@@ -136,8 +143,15 @@ represented as a ratio in the range [0, 1]."
   (with-agenda (agenda node)
     (set! (active? node) #f)
     (on-exit node)
-    (for-each-child deactivate node)
-    (reset-agenda)))
+    (for-each-child deactivate node)))
+
+(define-method (show (node <node>))
+  "Mark NODE as visible."
+  (set! (visible? node) #t))
+
+(define-method (hide (node <node>))
+  "Mark NODE as invisible."
+  (set! (visible? node) #f))
 
 
 ;;;
-- 
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