From 7148aa7270eeff605dfc72862649017fa450704f Mon Sep 17 00:00:00 2001
From: Nader Jawad <njawad@google.com>
Date: Wed, 31 Mar 2021 13:11:57 -0700
Subject: [PATCH] Stretch breaks on wembley

Work around GPU driver issues on Wembley.
Refactor the overscroll stretch shader to
explicitly return values in the helper methodsd
instead of using out parameters to store the
result.

Fixes: 182566543
Test: manual
Change-Id: Ib9c57d7cb3de06bc7155fa2af364d70cbf2ea812
---
 libs/hwui/effects/StretchEffect.cpp | 32 ++++++++++++++---------------
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/libs/hwui/effects/StretchEffect.cpp b/libs/hwui/effects/StretchEffect.cpp
index 9e4fb8fc9b352..0804e0aec2789 100644
--- a/libs/hwui/effects/StretchEffect.cpp
+++ b/libs/hwui/effects/StretchEffect.cpp
@@ -58,8 +58,7 @@ static const SkString stretchShader = SkString(R"(
     uniform float viewportWidth; // target height in pixels
     uniform float viewportHeight; // target width in pixels
 
-    void computeOverscrollStart(
-        out float outPos,
+    float computeOverscrollStart(
         float inPos,
         float overscroll,
         float uStretchAffectedDist,
@@ -68,11 +67,10 @@ static const SkString stretchShader = SkString(R"(
         float offsetPos = uStretchAffectedDist - inPos;
         float posBasedVariation = smoothstep(0., uStretchAffectedDist, offsetPos);
         float stretchIntensity = overscroll * posBasedVariation;
-        outPos = distanceStretched - (offsetPos / (1. + stretchIntensity));
+        return distanceStretched - (offsetPos / (1. + stretchIntensity));
     }
 
-    void computeOverscrollEnd(
-        out float outPos,
+    float computeOverscrollEnd(
         float inPos,
         float overscroll,
         float reverseStretchDist,
@@ -82,21 +80,23 @@ static const SkString stretchShader = SkString(R"(
         float offsetPos = inPos - reverseStretchDist;
         float posBasedVariation = (smoothstep(0., uStretchAffectedDist, offsetPos));
         float stretchIntensity = (-overscroll) * posBasedVariation;
-        outPos = 1 - (distanceStretched - (offsetPos / (1. + stretchIntensity)));
+        return 1 - (distanceStretched - (offsetPos / (1. + stretchIntensity)));
     }
 
-    void computeOverscroll(
-        out float outPos,
+    // Prefer usage of return values over out parameters as it enables
+    // SKSL to properly inline method calls and works around potential GPU
+    // driver issues on Wembly. See b/182566543 for details
+    float computeOverscroll(
         float inPos,
         float overscroll,
         float uStretchAffectedDist,
         float distanceStretched,
         float distanceDiff
     ) {
-        if (overscroll > 0) {
+      float outPos = inPos;
+      if (overscroll > 0) {
             if (inPos <= uStretchAffectedDist) {
-                computeOverscrollStart(
-                  outPos,
+                outPos = computeOverscrollStart(
                   inPos,
                   overscroll,
                   uStretchAffectedDist,
@@ -109,8 +109,7 @@ static const SkString stretchShader = SkString(R"(
         if (overscroll < 0) {
             float stretchAffectedDist = 1. - uStretchAffectedDist;
             if (inPos >= stretchAffectedDist) {
-                computeOverscrollEnd(
-                  outPos,
+                outPos = computeOverscrollEnd(
                   inPos,
                   overscroll,
                   stretchAffectedDist,
@@ -121,6 +120,7 @@ static const SkString stretchShader = SkString(R"(
                 outPos = -distanceDiff + inPos;
             }
         }
+        return outPos;
     }
 
     vec4 main(vec2 coord) {
@@ -135,16 +135,14 @@ static const SkString stretchShader = SkString(R"(
         inV += uScrollY;
         outU = inU;
         outV = inV;
-        computeOverscroll(
-            outU,
+        outU = computeOverscroll(
             inU,
             uOverscrollX,
             uStretchAffectedDistX,
             uDistanceStretchedX,
             uDistDiffX
         );
-        computeOverscroll(
-            outV,
+        outV = computeOverscroll(
             inV,
             uOverscrollY,
             uStretchAffectedDistY,