From d1b91f8037f99bbb26a51f6d7b720f23f6358aad Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sun, 31 Jul 2022 12:39:49 -0400
Subject: node-2d: Apply local matrix when computing bounding box.

---
 starling/node-2d.scm | 42 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/starling/node-2d.scm b/starling/node-2d.scm
index 005d7f1..00cbf4b 100644
--- a/starling/node-2d.scm
+++ b/starling/node-2d.scm
@@ -395,16 +395,46 @@
 (define-method (on-child-resize (node <node-2d>) child)
   #t)
 
-;; TODO: Take rotation and skew into consideration.
 (define-method (refresh-bounding-box (node <node-2d>))
   (let ((bb (bounding-box node))
         (p (position node))
         (o (origin node))
-        (s (scale node)))
-    (set-rect-x! bb (- (vec2-x p) (vec2-x o)))
-    (set-rect-y! bb (- (vec2-y p) (vec2-y o)))
-    (set-rect-width! bb (* (width node) (vec2-x s)))
-    (set-rect-height! bb (* (height node) (vec2-y s)))
+        (r (rotation node))
+        (k (skew node))
+        (w (width node))
+        (h (height node)))
+    (if (and (= r 0.0)
+             (= (vec2-x k) 0.0)
+             (= (vec2-y k) 0.0))
+        ;; Fast path: Node is axis-aligned and bounding box
+        ;; calculation is easy peasy.
+        (let ((s (scale node)))
+          (set-rect-x! bb (- (vec2-x p) (vec2-x o)))
+          (set-rect-y! bb (- (vec2-y p) (vec2-y o)))
+          (set-rect-width! bb (* w (vec2-x s)))
+          (set-rect-height! bb (* h (vec2-y s))))
+        ;; Slow path: Node is rotated, skewed, or both.
+        (let* ((m (local-matrix node))
+               (x0 (- (vec2-x p) (vec2-x o)))
+               (y0 (- (vec2-y p) (vec2-y o)))
+               (x1 (+ x0 w))
+               (y1 (+ y0 h))
+               (x2 (matrix4-transform-x m x0 y0))
+               (y2 (matrix4-transform-y m x0 y0))
+               (x3 (matrix4-transform-x m x1 y0))
+               (y3 (matrix4-transform-y m x1 y0))
+               (x4 (matrix4-transform-x m x1 y1))
+               (y4 (matrix4-transform-y m x1 y1))
+               (x5 (matrix4-transform-x m x0 y1))
+               (y5 (matrix4-transform-y m x0 y1))
+               (xmin (min x2 x3 x4 x5))
+               (ymin (min y2 y3 y4 y5))
+               (xmax (max x2 x3 x4 x5))
+               (ymax (max y2 y3 y4 y5)))
+          (set-rect-x! bb xmin)
+          (set-rect-y! bb ymin)
+          (set-rect-width! bb (- xmax xmin))
+          (set-rect-height! bb (- ymax ymin))))
     (set! (dirty-bounding-box? node) #f)))
 
 (define-method (on-change (node <node-2d>) slot old new)
-- 
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