Move matrix + silhouette updates into method

src/Drawable.js

@@ -452,6 +452,8 @@ class Drawable {
 
     /**
      * Check if the world position touches the skin.
+     * The caller is responsible for ensuring this drawable's inverse matrix & its skin's silhouette are up-to-date.
+     * @see updateCPURenderAttributes
      * @param {twgl.v3} vec World coordinate vector.
      * @return {boolean} True if the world position touches the skin.
      */
@@ -632,6 +634,15 @@ class Drawable {
         }
     }
 
+    /**
+     * Update everything necessary to render this drawable on the CPU.
+     */
+    updateCPURenderAttributes () {
+        this.updateMatrix();
+        // CPU rendering always occurs at the "native" size, so no need to scale up this._scale
+        if (this.skin) this.skin.updateSilhouette(this._scale);
+    }
+
     /**
      * Respond to an internal change in the current Skin.
      * @private
@@ -676,6 +687,8 @@ class Drawable {
 
     /**
      * Sample a color from a drawable's texture.
+     * The caller is responsible for ensuring this drawable's inverse matrix & its skin's silhouette are up-to-date.
+     * @see updateCPURenderAttributes
      * @param {twgl.v3} vec The scratch space [x,y] vector
      * @param {Drawable} drawable The drawable to sample the texture from
      * @param {Uint8ClampedArray} dst The "color4b" representation of the texture at point.