From 3932063bc75dc1e4efc2c428ca208d2e2290164d Mon Sep 17 00:00:00 2001
From: ztenghui <ztenghui@google.com>
Date: Wed, 12 Nov 2014 10:56:15 -0800
Subject: [PATCH] Shadow: Fix the crash in spot shadow

Fix the crash from searching for closest umbra vertex by initialized the
starting index correctly.

Fix another potential crash related to ray intersection by introducing epsilon.

b/18315089

Change-Id: I9ac9a781a885701a8388714d44f79a1d905e5d33
---
 libs/hwui/SpotShadow.cpp | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/libs/hwui/SpotShadow.cpp b/libs/hwui/SpotShadow.cpp
index e8f1b9aaa03a..b2dd8991ed23 100644
--- a/libs/hwui/SpotShadow.cpp
+++ b/libs/hwui/SpotShadow.cpp
@@ -677,11 +677,13 @@ inline int getClosestUmbraIndex(const Vector2& pivot, const Vector2* polygon, in
     return resultIndex;
 }
 
+// Allow some epsilon here since the later ray intersection did allow for some small
+// floating point error, when the intersection point is slightly outside the segment.
 inline bool sameDirections(bool isPositiveCross, float a, float b) {
     if (isPositiveCross) {
-        return a >= 0 && b >= 0;
+        return a >= -EPSILON && b >= -EPSILON;
     } else {
-        return a <= 0 && b <= 0;
+        return a <= EPSILON && b <= EPSILON;
     }
 }
 
@@ -721,22 +723,23 @@ inline void genNewPenumbraAndPairWithUmbra(const Vector2* penumbra, int penumbra
         // For current penumbra vertex, starting from previousClosestUmbraIndex,
         // then check the next one until the distance increase.
         // The last one before the increase is the umbra vertex we need to pair with.
-        int currentUmbraIndex = previousClosestUmbraIndex;
-        float currentLengthSquared = (currentPenumbraVertex - umbra[currentUmbraIndex]).lengthSquared();
-        int currentClosestUmbraIndex = -1;
+        float currentLengthSquared =
+                (currentPenumbraVertex - umbra[previousClosestUmbraIndex]).lengthSquared();
+        int currentClosestUmbraIndex = previousClosestUmbraIndex;
         int indexDelta = 0;
         for (int j = 1; j < umbraLength; j++) {
             int newUmbraIndex = (previousClosestUmbraIndex + j) % umbraLength;
             float newLengthSquared = (currentPenumbraVertex - umbra[newUmbraIndex]).lengthSquared();
             if (newLengthSquared > currentLengthSquared) {
-                currentClosestUmbraIndex = (previousClosestUmbraIndex + j - 1) % umbraLength;
+                // currentClosestUmbraIndex is the umbra vertex's index which has
+                // currently found smallest distance, so we can simply break here.
                 break;
             } else {
                 currentLengthSquared = newLengthSquared;
                 indexDelta++;
+                currentClosestUmbraIndex = newUmbraIndex;
             }
         }
-        LOG_ALWAYS_FATAL_IF(currentClosestUmbraIndex == -1, "Can't find a closet umbra vertext at all");
 
         if (indexDelta > 1) {
             // For those umbra don't have  penumbra, generate new penumbra vertices by interpolation.
@@ -810,6 +813,9 @@ inline bool genPolyToCentroid(const Vector2* poly2d, int polyLength,
         const Vector2& centroid, Vector2* polyToCentroid) {
     for (int j = 0; j < polyLength; j++) {
         polyToCentroid[j] = poly2d[j] - centroid;
+        // Normalize these vectors such that we can use epsilon comparison after
+        // computing their cross products with another normalized vector.
+        polyToCentroid[j].normalize();
     }
     float refCrossProduct = 0;
     for (int j = 0; j < polyLength; j++) {
-- 
2.11.0