Attempt to stabilize shadow_utils GM for replay configs

Change-Id: I0ed15ab102fa1e0a364d5f3a953bedd8afbda3c3
Reviewed-on: https://skia-review.googlesource.com/8853
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/gm/shadowutils.cpp b/gm/shadowutils.cpp
index 96554f10e7..fd02d92133 100644
--- a/gm/shadowutils.cpp
+++ b/gm/shadowutils.cpp
@@ -8,6 +8,7 @@
 #include "gm.h"
 #include "SkCanvas.h"
 #include "SkPath.h"
+#include "SkMutex.h"
 #include "SkShadowUtils.h"
 
 void draw_shadow(SkCanvas* canvas, const SkPath& path, int height, SkColor color, SkPoint3 lightPos,
@@ -22,6 +23,14 @@ static constexpr int kW = 700;
 static constexpr int kH = 800;
 
 DEF_SIMPLE_GM(shadow_utils, canvas, kW, kH) {
+    // SkShadowUtils uses a cache of SkVertices meshes. The vertices are created in a local
+    // coordinate system and then translated when reused. The coordinate system depends on
+    // parameters to the generating draw. To avoid slight rendering differences due to this property
+    // we only allow one thread into this GM at a time and we reset the cache before each run.
+    static SkMutex gMutex;
+    SkAutoMutexAcquire mutexLock(&gMutex);
+    SkShadowUtils::ClearCache();
+
     SkTArray<SkPath> paths;
     paths.push_back().addRoundRect(SkRect::MakeWH(50, 50), 10, 10);
     SkRRect oddRRect;