From b0acea9f35b55122e9ee11bc7a945634b0ccbba2 Mon Sep 17 00:00:00 2001
From: DD Liu <liudi@media.mit.edu>
Date: Thu, 13 Aug 2020 14:53:13 -0400
Subject: [PATCH] Pull in parts of pull 479 which move clamping to texture
 space into silhouette

---
 src/Drawable.js   | 14 +-------------
 src/Silhouette.js | 30 ++++++++++++++++++++----------
 2 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/src/Drawable.js b/src/Drawable.js
index 9e58ffb..74fb81d 100644
--- a/src/Drawable.js
+++ b/src/Drawable.js
@@ -712,8 +712,7 @@ 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. This will be clamped to the texture space, to match the
-     *     GL code (See https://github.com/LLK/scratch-render/blob/develop/src/BitmapSkin.js#L88)
+     * @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.
      * @param {number} [effectMask] A bitmask for which effects to use. Optional.
@@ -721,17 +720,6 @@ class Drawable {
      */
     static sampleColor4b (vec, drawable, dst, effectMask) {
         const localPosition = getLocalPosition(drawable, vec);
-        if (localPosition[0] < 0) {
-            localPosition[0] = 0;
-        } else if (localPosition[0] > 1) {
-            localPosition[0] = 1;
-        }
-
-        if (localPosition[1] < 0) {
-            localPosition[1] = 0;
-        } else if (localPosition[1] > 1) {
-            localPosition[1] = 1;
-        }
         const textColor =
         // commenting out to only use nearest for now
         // drawable.useNearest() ?
diff --git a/src/Silhouette.js b/src/Silhouette.js
index 08e7120..b96348a 100644
--- a/src/Silhouette.js
+++ b/src/Silhouette.js
@@ -10,6 +10,11 @@
  */
 let __SilhouetteUpdateCanvas;
 
+// Optimized Math.min and Math.max for integers;
+// taken from https://web.archive.org/web/20190716181049/http://guihaire.com/code/?p=549
+const intMin = (i, j) => j ^ ((i ^ j) & ((i - j) >> 31));
+const intMax = (i, j) => i ^ ((i ^ j) & ((i - j) >> 31));
+
 /**
  * Internal helper function (in hopes that compiler can inline).  Get a pixel
  * from silhouette data, or 0 if outside it's bounds.
@@ -40,13 +45,18 @@ const __cornerWork = [
 /**
  * Get the color from a given silhouette at an x/y local texture position.
  * Multiply color values by alpha for proper blending.
- * @param {Silhouette} The silhouette to sample.
- * @param {number} x X position of texture (0-1).
- * @param {number} y Y position of texture (0-1).
+ * @param {Silhouette} $0 The silhouette to sample.
+ * @param {number} x X position of texture [0, width).
+ * @param {number} y Y position of texture [0, height).
  * @param {Uint8ClampedArray} dst A color 4b space.
  * @return {Uint8ClampedArray} The dst vector.
  */
 const getColor4b = ({_width: width, _height: height, _colorData: data}, x, y, dst) => {
+    // Clamp coords to edge, matching GL_CLAMP_TO_EDGE.
+    // (See github.com/LLK/scratch-render/blob/954cfff02b08069a082cbedd415c1fecd9b1e4fb/src/BitmapSkin.js#L88)
+    x = intMax(0, intMin(x, width - 1));
+    y = intMax(0, intMin(y, height - 1));
+
     // 0 if outside bounds, otherwise read from data.
     if (x >= width || y >= height || x < 0 || y < 0) {
         return dst.fill(0);
@@ -64,17 +74,17 @@ const getColor4b = ({_width: width, _height: height, _colorData: data}, x, y, ds
 /**
  * Get the color from a given silhouette at an x/y local texture position.
  * Do not multiply color values by alpha, as it has already been done.
- * @param {Silhouette} The silhouette to sample.
- * @param {number} x X position of texture (0-1).
- * @param {number} y Y position of texture (0-1).
+ * @param {Silhouette} $0 The silhouette to sample.
+ * @param {number} x X position of texture [0, width).
+ * @param {number} y Y position of texture [0, height).
  * @param {Uint8ClampedArray} dst A color 4b space.
  * @return {Uint8ClampedArray} The dst vector.
  */
 const getPremultipliedColor4b = ({_width: width, _height: height, _colorData: data}, x, y, dst) => {
-    // 0 if outside bounds, otherwise read from data.
-    if (x >= width || y >= height || x < 0 || y < 0) {
-        return dst.fill(0);
-    }
+    // Clamp coords to edge, matching GL_CLAMP_TO_EDGE.
+    x = intMax(0, intMin(x, width - 1));
+    y = intMax(0, intMin(y, height - 1));
+
     const offset = ((y * width) + x) * 4;
     dst[0] = data[offset];
     dst[1] = data[offset + 1];