commit 7148aa7270eeff605dfc72862649017fa450704f
author Nader Jawad <njawad@google.com> Wed Mar 31 13:11:57 2021 -0700
committer Nader Jawad <njawad@google.com> Wed Mar 31 14:27:12 2021 -0700
tree 420e7ee6e2eab21df9461ab33da9d68353504d19
parent caab1b26a378664947fc2ede6aa47c65ead16eaf

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

diff --git a/libs/hwui/effects/StretchEffect.cpp b/libs/hwui/effects/StretchEffect.cpp
index 9e4fb8f..0804e0ae 100644
--- a/libs/hwui/effects/StretchEffect.cpp
+++ b/libs/hwui/effects/StretchEffect.cpp
@@ -58,8 +58,7 @@
     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 @@
         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 @@
         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 @@
         if (overscroll < 0) {
             float stretchAffectedDist = 1. - uStretchAffectedDist;
             if (inPos >= stretchAffectedDist) {
-                computeOverscrollEnd(
-                  outPos,
+                outPos = computeOverscrollEnd(
                   inPos,
                   overscroll,
                   stretchAffectedDist,
@@ -121,6 +120,7 @@
                 outPos = -distanceDiff + inPos;
             }
         }
+        return outPos;
     }
 
     vec4 main(vec2 coord) {
@@ -135,16 +135,14 @@
         inV += uScrollY;
         outU = inU;
         outV = inV;
-        computeOverscroll(
-            outU,
+        outU = computeOverscroll(
             inU,
             uOverscrollX,
             uStretchAffectedDistX,
             uDistanceStretchedX,
             uDistDiffX
         );
-        computeOverscroll(
-            outV,
+        outV = computeOverscroll(
             inV,
             uOverscrollY,
             uStretchAffectedDistY,