Initialialize AABB Rectangle

src/BitmapSkin.js

@@ -62,10 +62,11 @@ class BitmapSkin extends Skin {
     /**
      * Get the bounds of the drawable for determining its fenced position.
      * @param {Array<number>} drawable - The Drawable instance this skin is using.
+     * @param {?Rectangle} result - Optional destination for bounds calculation.
      * @return {!Rectangle} The drawable's bounds. For compatibility with Scratch 2, we always use getAABB for bitmaps.
      */
-    getFenceBounds (drawable) {
-        return drawable.getAABB();
+    getFenceBounds (drawable, result) {
+        return drawable.getAABB(result);
     }
 
     /**

src/Drawable.js

@@ -451,9 +451,10 @@ class Drawable {
      * This function applies the transform matrix to the known convex hull,
      * and then finds the minimum box along the axes.
      * Before calling this, ensure the renderer has updated convex hull points.
+     * @param {?Rectangle} result optional destination for bounds calculation
      * @return {!Rectangle} Bounds for a tight box around the Drawable.
      */
-    getBounds () {
+    getBounds (result) {
         if (this.needsConvexHullPoints()) {
             throw new Error('Needs updated convex hull points before bounds calculation.');
         }
@@ -462,18 +463,19 @@ class Drawable {
         }
         const transformedHullPoints = this._getTransformedHullPoints();
         // Search through transformed points to generate box on axes.
-        const bounds = new Rectangle();
-        bounds.initFromPointsAABB(transformedHullPoints);
-        return bounds;
+        result = result || new Rectangle();
+        result.initFromPointsAABB(transformedHullPoints);
+        return result;
     }
 
     /**
      * Get the precise bounds for the upper 8px slice of the Drawable.
      * Used for calculating where to position a text bubble.
      * Before calling this, ensure the renderer has updated convex hull points.
+     * @param {?Rectangle} result optional destination for bounds calculation
      * @return {!Rectangle} Bounds for a tight box around a slice of the Drawable.
      */
-    getBoundsForBubble () {
+    getBoundsForBubble (result) {
         if (this.needsConvexHullPoints()) {
             throw new Error('Needs updated convex hull points before bubble bounds calculation.');
         }
@@ -485,9 +487,9 @@ class Drawable {
         const maxY = Math.max.apply(null, transformedHullPoints.map(p => p[1]));
         const filteredHullPoints = transformedHullPoints.filter(p => p[1] > maxY - slice);
         // Search through filtered points to generate box on axes.
-        const bounds = new Rectangle();
-        bounds.initFromPointsAABB(filteredHullPoints);
-        return bounds;
+        result = result || new Rectangle();
+        result.initFromPointsAABB(filteredHullPoints);
+        return result;
     }
 
     /**
@@ -497,35 +499,32 @@ class Drawable {
      * which is tightly snapped to account for a Drawable's transparent regions.
      * `getAABB` returns a much less accurate bounding box, but will be much
      * faster to calculate so may be desired for quick checks/optimizations.
+     * @param {?Rectangle} result optional destination for bounds calculation
      * @return {!Rectangle} Rough axis-aligned bounding box for Drawable.
      */
-    getAABB () {
+    getAABB (result) {
         if (this._transformDirty) {
             this._calculateTransform();
         }
         const tm = this._uniforms.u_modelMatrix;
-        const bounds = new Rectangle();
-        bounds.initFromPointsAABB([
-            twgl.m4.transformPoint(tm, [-0.5, -0.5, 0]),
-            twgl.m4.transformPoint(tm, [0.5, -0.5, 0]),
-            twgl.m4.transformPoint(tm, [-0.5, 0.5, 0]),
-            twgl.m4.transformPoint(tm, [0.5, 0.5, 0])
-        ]);
-        return bounds;
+        result = result || new Rectangle();
+        result.initFromModelMatrix(tm);
+        return result;
     }
 
     /**
      * Return the best Drawable bounds possible without performing graphics queries.
      * I.e., returns the tight bounding box when the convex hull points are already
      * known, but otherwise return the rough AABB of the Drawable.
+     * @param {?Rectangle} result optional destination for bounds calculation
      * @return {!Rectangle} Bounds for the Drawable.
      */
-    getFastBounds () {
+    getFastBounds (result) {
         this.updateMatrix();
         if (!this.needsConvexHullPoints()) {
-            return this.getBounds();
+            return this.getBounds(result);
         }
-        return this.getAABB();
+        return this.getAABB(result);
     }
 
     /**

src/Rectangle.js

@@ -54,6 +54,105 @@ class Rectangle {
         }
     }
 
+    /**
+     * Initialize a Rectangle to a 1 unit square transformed by a model matrix.
+     * @param {Array.<number>} m A 4x4 matrix to transform the rectangle by.
+     */
+    initFromModelMatrix (m) {
+        // Treat this function like we are transforming a vector with each
+        // component set to 0.5 by a matrix m.
+        // const v0 = 0.5;
+        // const v1 = 0.5;
+        // const v2 = 0.5;
+
+        // Of the matrix to do this in 2D space, instead of the 3D provided by
+        // the matrix, we need the 2x2 "top left" that represents the scale and
+        // rotation ...
+        const m00 = m[(0 * 4) + 0];
+        const m01 = m[(0 * 4) + 1];
+        const m10 = m[(1 * 4) + 0];
+        const m11 = m[(1 * 4) + 1];
+        // ... and the 1x2 "top right" that represents position.
+        const m30 = m[(3 * 4) + 0];
+        const m31 = m[(3 * 4) + 1];
+
+        // This is how we would normally transform the vector by the matrix.
+        // var determinant = v0 * m03 + v1 * m13 + v2 * m23 + m33;
+        // dst[0] = (v0 * m00 + v1 * m10 + v2 * m20 + m30) / determinant;
+        // dst[1] = (v0 * m01 + v1 * m11 + v2 * m21 + m31) / determinant;
+        // dst[2] = (v0 * m02 + v1 * m12 + v2 * m22 + m32) / determinant;
+
+        // We can skip the v2 multiplications and the determinant.
+
+        // Alternatively done with 4 vectors, those vectors would be reflected
+        // on the x and y axis. We can build those 4 vectors by transforming the
+        // parts of one vector and reflecting them on the axises after
+        // multiplication.
+
+        // const x0 = 0.5 * m00;
+        // const x1 = 0.5 * m10;
+        // const y0 = 0.5 * m01;
+        // const y1 = 0.5 * m11;
+
+        // const p0x = x0 + x1;
+        // const p0y = y0 + y1;
+        // const p1x = -x0 + x1;
+        // const p1y = -y0 + y1;
+        // const p2x = -x0 + -x1;
+        // const p2y = -y0 + -y1;
+        // const p3x = x0 + -x1;
+        // const p3y = y0 + -y1;
+
+        // Since we want to reduce those 4 points to a min and max for each
+        // axis, we can use those multiplied components to build the min and max
+        // values without comparing the points.
+
+        // We can start by getting the min and max for each of all the points.
+        // const left = Math.min(x0 + x1, -x0 + x1, -x0 + -x1, x0 + -x1);
+        // const right = Math.max(x0 + x1, -x0 + x1, -x0 + -x1, x0 + -x1);
+        // const top = Math.max(y0 + y1, -y0 + y1, -y0 + -y1, y0 + -y1);
+        // const bottom = Math.min(y0 + y1, -y0 + y1, -y0 + -y1, y0 + -y1);
+
+        // Each of those can be replaced with min and max operations on the 0
+        // and 1 matrix output components.
+        // const left = Math.min(x0, -x0) + Math.min(x1, -x1);
+        // const right = Math.max(x0, -x0) + Math.max(x1, -x1);
+        // const top = Math.max(y0, -y0) + Math.max(y1, -y1);
+        // const bottom = Math.min(y0, -y0) + Math.min(y1, -y1);
+
+        // And they can be replaced with absolute values.
+        // const left = -Math.abs(x0) + -Math.abs(x1);
+        // const right = Math.abs(x0) + Math.abs(x1);
+        // const top = Math.abs(y0) + Math.abs(y1);
+        // const bottom = -Math.abs(y0) + -Math.abs(y1);
+
+        // And those with positive and negative sums of the absolute values.
+        // const left = -(Math.abs(x0) + Math.abs(x1));
+        // const right = +(Math.abs(x0) + Math.abs(x1));
+        // const top = +(Math.abs(y0) + Math.abs(y1));
+        // const bottom = -(Math.abs(y0) + -Math.abs(y1));
+
+        // We can perform those sums once and reuse them for the bounds.
+        // const x = Math.abs(x0) + Math.abs(x1);
+        // const y = Math.abs(y0) + Math.abs(y1);
+        // const left = -x;
+        // const right = x;
+        // const top = y;
+        // const bottom = -y;
+
+        // Building those absolute sums for the 0.5 vector components by the
+        // matrix components ...
+        const x = Math.abs(0.5 * m00) + Math.abs(0.5 * m10);
+        const y = Math.abs(0.5 * m01) + Math.abs(0.5 * m11);
+
+        // And adding them to the position components in the matrices
+        // initializes our Rectangle.
+        this.left = -x + m30;
+        this.right = x + m30;
+        this.top = y + m31;
+        this.bottom = -y + m31;
+    }
+
     /**
      * Determine if this Rectangle intersects some other.
      * Note that this is a comparison assuming the Rectangle was

src/RenderWebGL.js

@@ -16,6 +16,7 @@ const log = require('./util/log');
 
 const __isTouchingDrawablesPoint = twgl.v3.create();
 const __candidatesBounds = new Rectangle();
+const __fenceBounds = new Rectangle();
 const __touchingColor = new Uint8ClampedArray(4);
 const __blendColor = new Uint8ClampedArray(4);
 
@@ -1357,7 +1358,7 @@ class RenderWebGL extends EventEmitter {
 
         const dx = x - drawable._position[0];
         const dy = y - drawable._position[1];
-        const aabb = drawable._skin.getFenceBounds(drawable);
+        const aabb = drawable._skin.getFenceBounds(drawable, __fenceBounds);
         const inset = Math.floor(Math.min(aabb.width, aabb.height) / 2);
 
         const sx = this._xRight - Math.min(FENCE_WIDTH, inset);
@@ -1627,14 +1628,14 @@ class RenderWebGL extends EventEmitter {
             }
 
             twgl.setUniforms(currentShader, uniforms);
-            
+
             /* adjust blend function for this skin */
             if (drawable.skin.hasPremultipliedAlpha){
                 gl.blendFuncSeparate(gl.ONE, gl.ONE_MINUS_SRC_ALPHA, gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
             } else {
                 gl.blendFuncSeparate(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA, gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
             }
-            
+
             twgl.drawBufferInfo(gl, this._bufferInfo, gl.TRIANGLES);
         }
 

src/Skin.js

@@ -146,10 +146,11 @@ class Skin extends EventEmitter {
     /**
      * Get the bounds of the drawable for determining its fenced position.
      * @param {Array<number>} drawable - The Drawable instance this skin is using.
+     * @param {?Rectangle} result - Optional destination for bounds calculation.
      * @return {!Rectangle} The drawable's bounds.
      */
-    getFenceBounds (drawable) {
-        return drawable.getFastBounds();
+    getFenceBounds (drawable, result) {
+        return drawable.getFastBounds(result);
     }
 
     /**